Concluding a Two-Part Study Testing the Scanning Quality Of Nine

Transcription

Volume 28, Number 11
The Seybold Report on Publishing Systems
Concluding a Two-Part Study
Testing the Scanning Quality
Of Nine High-End Flatbeds
T
HIS ARTICLE concludes our report on our tests of nine highend flatbed scanners. We began with an analysis of productivity aspects of scanning (see Vol. 28, No. 9). Here we focus
on the interlocking issues of resolution and image quality.
To recap our productivity results, none of the nine machines
excelled in all areas tested. The Scitex EverSmart Pro did well on
all tests and took top honors in the batch scanning of 20 transparencies. In scanning a single transparency at 250%, the ScanView
ScanMate F8 Plus was fastest, followed by the Heidelberg Prepress
QuickStep. In scanning a single transparency at 850%, the Fuji
Lanovia C-550 was fastest, followed by the F8 Plus.
As you will see from the results presented here, the most productive scanners in the first phase weren’t necessarily the ones producing the best quality. Potential buyers will have to balance quality
and productivity factors in shopping for a scanner.
About the test participants
The participating scanners were Agfa’s AgfaScan T5000; Fuji’s
Lanovia C-550; Heidelberg’s QuickStep, Topaz and Topaz IX;
Imacon’s FlexTight Precision II; Purup-Eskofot’s Eskoscan 1318;
ScanView’s ScanMate F8 Plus; Screen’s Cézanne; and Scitex’s EverSmart Pro.
Each vendor was asked to sign a formal confirmation that the
models tested, and therefore the results obtained, were truly representative of what a customer could expect in terms of performance and productivity. We tested production models rather than
devices optimized in the lab and are confident that users will be
able to replicate the results we have achieved. Because of the timing of our tests relative to Ipex scanner introductions, some tested
models are no longer the latest offered by their vendors.
The tests were conducted by Seybold Publications in conjunction with AGI of Sweden (see sidebar, p. 12).
Test Objectives
Evaluating a scanner’s performance is inevitably highly subjective.
Whether a device is suitable or not depends upon the demands of
the application. The technology a scanner incorporates, its configuration and its capabilities can be used as key differentiators, however,
when comparing a collection of highly competitive machines.
In our previous article, our focus was on objective timing data.
In this article, though, we get into the subjective area of image
quality. We wanted to learn more about the usefulness of the various technical specifications attributed to each machine, especially
the manufacturer’s stated resolution, as a guide to the quality it
can produce.
Test images. Our test images included a 4×5-inch color transparency
depicting fabrics, a glass frequency-resolution target, and a Swedish bank
note.
Resolution and quality issues
Resolution is often cited as a measure of quality and, indeed, is a
useful indicator of what constitutes a “high-end” device. The resolution of the optical systems in high-end devices currently approaches
the resolving power of good analog film. High-quality, low-speed
analog film (which requires a lot of light for exposure) is capable
of creating a very detailed image. This is because the photosensitive grain in the film’s surface emulsion is extremely fine and abundant, and can therefore respond across a wide spectrum of light
intensities to yield sharp and detailed images.
It is pointless to scan at resolutions much finer than the size
of the film grain. All that is achieved is a better rendition of the
grain; there is no improvement in the image. High-speed, lowquality film has larger grain, which is easily resolved by a good
scanner. With high-quality film, such as the transparencies we
scanned in our tests, it takes a good optical system to resolve the
grain. But, as you will see, the flatbeds we tested have mostly reached
the point where further increases in resolution would be wasted
on even high-quality film. Beyond a certain point, additional
11
March 2, 1999
Interpolation algorithms work very well for
50% enlargements and well enough for
enlargements of even 200% or 300%, but the
results are rarely acceptable much above this.
resolution is not a significant indicator of quality, nor can optical
resolution alone be used as an indicator of quality.
The quality of image obtained can be affected by other factors, including vibration in the scanning mechanism, the quality of
the sensor and its supporting electronics, and the software that
processes the scanned image.
In the vertical (or y) direction, the resolution is determined by
the number of incremental steps made either by the optical system
or the scanning bed. This vertical resolution can be different from
the horizontal resolution, which is why some manufacturers state
different resolutions in the two directions (e.g., Agfa, with its
AgfaScan T5000 resolution of 2,500×5,000 ppi).
Calculating resolution. In flatbed scanners, the light-sensitive
element is a CCD array. A scanner’s maximum optical resolution is
a function of the number of elements in the CCD array and the
width of the smallest area that the optical system can project onto
the CCD. (In the case of the machines we tested, there were typically 8,000 elements, although the number varied from 6,000 to
10,500.)
A scanner with a lens system that can project a width of 40mm
(1.6 inches) onto an 8,000-element array has an optical resolution
of 200 lines per millimeter (about 5,080 pixels per inch). This is
typical of the highest-resolution scanners in the group we tested,
comparable to the resolving power of good-quality film. For example, Kodachrome 25 Professional transparency film has a resolution in the range of 50–100 lines per millimeter. Scanner optics
can be designed with still higher resolution, but it is not useful.
In the end, quality is a function of resolution, the scanner’s
optical and electronic systems, and the control software. Although
high resolution is an indicator of the scanner’s optical capacity, it
is only one factor and cannot be used as an absolute measure of the
scanner’s ability to yield a pleasing result.
Interpolation. When an image must be scanned at a resolution
that differs from the available optical resolutions of the scanner,
the software must calculate the missing image details based on the
pixel information a scanner has been able to capture. This calculation, called interpolation, commonly occurs in these situations:
• If the degree of enlargement required is greater than the maximum optical resolution achievable with the scanner, interpolation may be used to reach the target resolution. This situation
can occur with scanners employing either zoom or fixed (nonzoom) lenses.
• With scanners employing fixed lenses, even if the desired resolution is lower than the maximum optical resolution of the scanner, the scanner may not be able to scan at the desired resolution.
(For example, if the machine’s scanning resolutions are 300, 600,
900, 1,200 and 2,400 ppi, it would have to interpolate to scan
at 1,800 ppi.)
• With scanners that operate at non-square resolutions (e.g., the
Agfa T5000’s 1,200×5,000 ppi), the final image must have a
resolution that is the same in both directions. To achieve this, it
must interpolate data in at least one direction.
Optical vs. interpolated resolution
It is important to understand the difference between optical and
interpolated resolution. On a conventional flatbed scanner, the optics
are positioned along a path that traverses the center of the scan
bed, with the CCD array oriented perpendicular to the path. As we
just saw, it is possible to calculate the optical resolution for a scanner based on the number of elements in the CCD array and the
minimum image width with which the optics are designed to work.
This can be called the resolution in the horizontal (or x) direction.
About AGI
AGI, which collaborated with Seybold Publications in testing
these scanners, was founded in 1970 and is now the dominant trade publisher for graphic arts professionals throughout
the Scandinavian countries. AGI produces six different magazines covering all aspects of the printing and publishing industries, from newspaper publishing to computer-based design.
Besides reporting on the major trends within the publishing
industry, AGI arranges seminars, conferences and exhibitions
and conducts regular technology tests.
The AGI testing program extends to output devices, including
presses as well as software and hardware used within the printing and publishing industries.
12
How good? Interpolation algorithms work very well for 50% enlargements and well enough for enlargements of even 200% or 300%,
but the results are rarely acceptable much above this. Some scanners
have raised the optical resolution in the vertical direction by increasing the number of steps at which data are captured. This can be useful for interpolation algorithms, but there is a point beyond which
interpolation adds irrelevant image data, creating unnecessarily large
file sizes while making little contribution to image quality.
All of the scanners we tested offer interpolated resolutions that
go beyond their optical resolutions. One of the questions we wanted
to answer was whether this additional interpolation is useful.
Our tests
We used the following eight tests in our evaluation of quality and
resolution. Participants were asked to perform as many of these
tests as they could, but were not obliged to complete all of them.
• A 4×5-inch test image scanned at 250% for a final resolution of
350 ppi (2×175 lpi).
• The same 4×5-inch image scanned at 850% for a final resolution
of 350 ppi.
• A crop of about 3×3cm in the center of this image at the highest
optical resolution stated in the scanner’s technical specifications.
• A chromium-plated, glass-platen Variable Frequency Resolution
Target rotated 10 degrees from the scan axis, at the highest optical
resolution.
The density range measures the breadth of
densities a scanner can capture, from the
minimum to the maximum.
• The Variable Frequency Resolution Target rotated 10 degrees
perpendicular to the scan axis, at the highest optical resolution.
• The Variable Frequency Resolution Target scanned at the highest interpolated resolution.
• The Variable Frequency Resolution Target scanned perpendicular to the scan axis at the highest interpolated resolution.
• A bank note scanned at 100%, with two 3×3cm crops, at the
highest optical resolution.
Samples. We have included in this issue some samples printed
from these test scans. They were printed on a sheet-fed offset press
onto 150-gsm Multiart Silk semigloss paper. Many additional
samples are included in our report Pixel Perfect: A Buyers’ Guide to
High-End Flatbed Scanners. (See the box at the end of this article
for information on how to obtain a copy.) Films were output on
a calibrated and linearized Scangraphic Othello imagesetter at 2,540
dpi. Images were output using elliptical screening.
Other factors in evaluating a scanner
We hope the results of this test suite will be useful to prospective
scanner purchasers, although they can play only one part in the
overall evaluation process. Other types of information can be gleaned
from the scanner’s specifications.
For example, if you want to output a variety of different image sizes from wildly variant input, you need to consider scanners
with wide enlargement and resolution ranges.
Density. The density range and density maximum are important
because they indicate a device’s ability to distinguish the extremes
of contrast within an image. They provide a measure of a device’s
ability to reproduce the tonal values in an image, from the darkest
shadow areas to the subtle nuances of very bright highlights.
The density maximum (“Dmax”) refers to the maximum
darkness or darkest point that a device can distinguish. In other
words, it measures a scanner’s ability to differentiate between the
tonal values in the very darkest area of an image. The density minimum (“Dmin”) measures the opposite extreme—the lightest point
that can be differentiated. Together, these figures are critical in
capturing red, green and blue (RGB) signals for color rendering.
The density range measures the breadth of densities a scanner
can capture, from the minimum to the maximum. A wide density
range allows the scanner to accurately capture images with diverse
densities, such as those with lots of highlight and shadow details.
A wide density range is necessary where scanning requires capturing great content detail amid extremes of density.
Other features. There are a host of other factors to consider,
many of which come under the general heading of scanner control—the software that is supplied with the scanner. Besides drivers
for the specific scanner with which the software is bundled, these
software products include many features to aid the operator in
obtaining the best quality scans with the least possible manual effort. They have become so sophisticated in recent years that it is
International Color Consortium
The International Color Consortium (ICC) is an international
committee comprising most of the major suppliers to the industry—Adobe, Agfa, Apple, Heidelberg Prepress and many
others. It was set up in 1993 to develop a standard means of
managing color production workflows across disparate devices,
including screens, digital cameras, scanners and output engines. Device independence was recognized as a necessary
requirement for color images produced in open environments.
Without the inherent control of a closed system, however, color
rendering is subject to the different behaviors of different
devices.
The organization wanted to design a production method
whereby color integrity could be preserved in multiple-user
environments. The idea was to standardize color handling in
modular environments so that its production was as predictable using open platforms as it had been using proprietary
systems.
The consortium’s approach has been to develop a deviceindependent profile format that is available to the entire industry. The format defines the characteristics of a particular
input or output device to enable subsequent processes to take
into account the color behavior of the capture or output technology. Tags written in the ICC format are attached to data
files so that when the files are opened any compensation for
variables in the rendering devices is automatically applied.
The idea is to normalize the presentation of color so that it
does not depend on the manner in which an input or output
device captures or presents color. This objective has now been
realized with the use of ICC profiling endorsed by the majority
of players in the industry.
For further details, contact the ICC at www.color.org.
difficult to evaluate them in comparative terms. In the section below,
we’ll attempt to characterize them and comment on some key
features, company by company.
In general, this software should support an application’s full
range of requirements, including functions such as descreening,
copydot scanning and color correction. It is also important to
consider how well the software operates within a managed workflow
that encompasses other applications, such as Photoshop, and how
well it supports ICC color workflows (see box).
Besides scanner control software, it is important to take into
account the training tools and vendor support, particularly in environments where experience with desktop imaging is limited.
A few other items to consider are these:
• Will the scanner accommodate the full range of media types that
are likely to be encountered, including the original sizes and
types, such as monochrome and color paper and film originals?
• Can it handle three-dimensional objects?
• Are its physical dimensions appropriate, particularly in environments where space is limited?
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March 2, 1999
The combination of foreground-background
controls with special palettes make the T5000
very quick, easy to use and quite productive,
particularly for novice users.
Scanners and Software Features
In our previous article, we summarized the characteristics of the
scanners we tested, including the technology they employ. Here,
we provide additional comments about the software that is provided with them. We haven’t attempted to rank the functionality
or ease of use of these programs.
Agfa AgfaScan T5000
According to Agfa’s estimates, the T5000 is capable of performing 25 scans per hour based when scanning 6×7cm originals
at 750 ppi. The T5000 comes with various image holders that can
be addressed for automated scanning.
Pricing, sales and testing. There are 650 T5000s in the field.
Initial shipments took place last July. The U.S. list price is $22,500.
The tests were conducted at Agfa’s facilities in Mortsel, Belgium, using a 266-MHz Macintosh G3 host computer with 288
MB of RAM and a 6-GB hard disk.
Agfa AgfaScan T5000 workflow without templates:
Bed scan => Auto crop=> Auto preview=> Corrections=> Batch or single scan
Apart from value for money, perhaps the T5000’s greatest attraction is the ColorExact scanner control software that comes with it. Agfa AgfaScan T5000 workflow with templates:
Auto preview=> Corrections=> Batch or single scan
Available for both the Mac and PC, this software is bundled with
the T5000 and the newly introduced XY-15 (which wasn’t included in our testing). It isn’t bundled with Agfa’s lower-end scanFuji Lanovia C-550
ners, which are accompanied by FotoLook software instead.
ColorExact has been designed for maximum productivity and
ease of use, but it includes some powerful tools. The user interface The Lanovia comes with a package called C-scan Control Softis simple and intuitive, based on collapsible, custom palettes for ware, which provides the user interface. This scanner is highly
access to the controls. The most frequently used tool sets can be automated with a library of setups based on a variety of original
stored with each image in these palettes, which can hold either types that provide the basis for specific scanner setups. These basic
setups have been configured according to media type and output
predefined settings or more complex, custom tool sets.
There are modules for batch background scanning to enable requirements. The library is extensible and the user can modify the
the operator to work with image analysis and corrections in the base setups and store them as new ones or create entirely new
foreground, as the scanner continues to capture data. The combi- setups from scratch.
Although the user can modify some scan
nation of foreground-background controls with
parameters, it is not possible to set the scan resothese special palettes can be used to make the
lution on the C-550. The scanner software calT5000 very quick, easy to use and quite proculates the optimum scanning resolution
ductive, particularly for novice users.
automatically based on the enlargement, scaling
Although ColorExact is designed to be fast
and output resolution selected by the operator.
and simple to use, it is full-featured. Apart from
C-scan actually restricts the device’s true scancontrols over UCR, GCR and color casts, it provides tools for USM, rotation alignment, conning resolution to avoid allowing interference
trolling the tonal range of an image, descreening,
by film grain, a restriction that Fuji or the user
and adjusting the highlight and shadow points
can remove via the preferences setting.
to enable dot percentages to suit each image to
The user interface has been designed spepress conditions. Up to 10 colors per image can
cifically for the C-550, although much of the
be modified selectively. A dynamic preview reunderlying color and image-processing technolflects changes or color-correction activity immeogy is based on the Crosfield Celsis scanner softdiately. A Dynamic Batch palette controls the
ware and is used also with Fuji’s drum scanners.
order in which images are scanned (adjustable
Fuji plans to support the ICC standard fully,
on the fly as the batch process continues).
although it currently offers no tools for creatColorExact provides tools for creating ICC
ing, importing or editing ICC profiles. These
profiles for input, the monitor or output. Agfa’s
will be available in the next software version due
ColorTune Pro software for color management
for release imminently.
also comes bundled with the T5000. ColorTune
This new software also will make it possible
Agfa’s AgfaScan T5000
Pro is used to calibrate all prepress components
to take up to three samples from a preview of a
within the system.
line-art scan and do a high-resolution scan of those sample areas.
An unusual T5000 feature is a preview scan initiated by a but- This can then be used to make a selective high-resolution scan of
ton on the scanner itself, rather than from within ColorExact. The critical areas in an image or page, using these subsamples as the
objective is for the scanner to start the preview immediately, while basis for setting sensitivity and threshold to ensure optimum rethe operator returns to the workstation, making it more productive. sults.
14
Heidelberg Prepress QuickStep
This feature only applies to line-art scans, which can be
difficult to set up if the original contains items
such as a wide variety of text styles or sizes,
positive and reverse text, and so on.
Fuji also has added
punched holes to its mounts
to enable automatic identification and to allow the image
acquisition to support copyholder profiles. The scanner software automatically captures either
the preview or high-resolution scan,
although the preview scan allows for
additional correction functions, if necessary. Automatic cropping can be based
either on the orientation of 35mm slides
within the copyholder or a selective scan initiated by the user on
certain images within the copyholder. Mixed setups also will be
possible.
These new features will be available initially for formats up to
A4. Full A3 support will be added in a subsequent release.
A C-Scan Plus module under development will support
copydot scanning using stitching technology. It will offer both
“excellent” and “normal” modes for scanning line art. Software
performance also will be enhanced in the next release, making
“normal” mode 60% faster and “excellent” mode 30% quicker than
they are in the current version.
C-Scan also supports batch scanning and a wide range of image
analysis and correction tools, aided by two levels of user interface:
a simple one for less-experienced users and an advanced one with
direct access to all settings.
Pricing, sales and testing information. The Lanovia C-550
is priced at £25,000 in the UK and $40,000 in the U.S. (not
including the copydot scanning option). More than 800 units have
been sold to date. Our testing was performed at Fuji’s Hemel
Hempstead, UK, facility using a 300-MHz Mac G3 with 128 MB
of RAM and a 4.2-GB hard disk.
Fuji Lanovia C-550 workflow:
Preview => Corrections=> Batch/single scan
Heidelberg (then Linotype-Hell) was one of the first companies
both to embrace the concept of working internally in the CIELAB
color space and to support the ICC standard. It got a major endorsement in 1995 when Apple decided to use its LinoColor color
matching module (CMM) as the default CMM in ColorSync. More
recently, Microsoft also opted for the LinoColor CMM in its ICM
(Image Color Management) system incorporated in Windows 98
and NT 5.0.
The full version of LinoColor currently is available only on
the Apple platform, but a Windows version is under development
and “Lite” versions for Windows already
are being distributed by Heidelberg CPS
under different names. A supplement
to LinoColor is the software suite
Color Open, used to produce
and edit ICC-profiles for the
monitor, scanner and output
devices.
LinoColor, which is the
scanner control software provided
with the QuickStep, comprises three main
software modules:
• ColorAssistant performs image analysis and
correction.
• GeoAssistant identifies and crops images automatically.
• JobAssistant supports batch scanning.
The user first performs an overview scan, after which manual
cropping takes place and a preview of the image is generated for
analysis and color correction. LinoColor includes many color reproduction features, although it is extremely simple to use.
The objective with the software design has been to turn scanning into a single-step operation. The operator works mainly within
the LCH color space (luminance, or brightness; chroma, or color
intensity; and hue), which was something of a revolution when
Linotype-Hell introduced it. Working with LCH values is supposed
to be much more intuitive than working in CMYK, which still is
quite common for scanner operators.
When the high-resolution scan is performed, the image is first
saved as a temporary file on the disk and then color-separated on
the fly, if necessary. As soon as an image has been analyzed, the
scanner starts the high-resolution scanning in background mode
while the operator continues with the analysis of additional images.
Three image-quality modes are available for the operator:
normal, which is the fastest, quality and excellent. The differences
are mainly in how many samples the scanner takes before the final
definition of pixel values is made. The more samples it makes, the
longer the process takes.
Heidelberg Prepress bases much of its image technology on
saving the images in a nonseparated format, preferably CIELAB. This
makes it easy to reuse the images under different printing conditions later, without rescanning.
An alternative to the manual steps described above is to let the
software perform all the steps automatically. Heidelberg Prepress
calls this “One Button Scanning.”
Pricing, sales and testing information. The QuickStep is
priced at $19,950 and sold through the normal Heidelberg Prepress
distribution channels.
Our testing was done at the company’s Kiel facility, using a
266-MHz G3 with 160 MB of RAM and a 6-GB Quantum hard disk
(all standard items from Apple) and SCSI connection.
Heidelberg PrePress QuickStep workflow:
Overview=> Crop=> Preview => Correct =>Scan
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March 2, 1999
Scanner Specifications (Prices in U.S. Dollars)
1
2
3
Copydot price is if purchased with scanner; scanner price includes control software.
Supplementary CDD array for copydot scanning.
This number was reported incorrectly in Part I, Vol. 28, No. 9, p. 5.
Model
Agfa AgfaScan T5000
Fuji Lanovia C-550
Heidelberg Prepress Topaz
Pixels in
CCD array
Optical Max. size of Bits per Dynamic
resolution original (mm)
color
range
10,200 2,500×5,000
Copydot? Price1 w.
Dmax
(price1) software
No $22,500
305×432
13
3.5D
3.7D
8,000
5,000
350×455
16
3.7D
3.9D Future opt. $39,500
10,500
2,400
305×432
14
3.4D
3.7D
No $19,950
8,000
5,080
305×457
16
3.7D
4.0D
Optional $36,000
12,0002
7,6202
305×457
16
3.7D
4.0D +$14,500 $47,500
for analysis and color correction, and finally a high-resolution scan. It isn’t possible
to start a batch until all
images have gone through
image analysis.
Pricing, sales and testing information. Because the model we tested
Imacon FlexTight Precision II
8,000
5,760
220×310
16
3.9D
3.9D
No $16,995
had a smaller format than
Purup-Eskofot Eskoscan 1318
6,000
5,080
279×439
16
3.6D
3.6D Standard $47,500
the other machines in our
ScanView ScanMate F8 Plus
8,640
4,000
297×432
16
3.7D
4.2D
$8,500 $33,495
study, it also had the lowScitex EverSmart Pro
8,000
3,175
305×432
14
3.7D
4.0D
$5,000 $34,950
est price: $16,995. (An A3
16
3.9D
3.9D
$6,000 $34,000
Screen Cézanne
8,000
5,300
340×5303
version was announced at
Ipex for about $25,000.)
Our tests were performed at Imacon’s Copenhagen office with
a 233-MHz G3 with 160 MB of RAM and a 4-GB Quantum hard
Like the QuickStep, the Topaz is sold with LinoColor software disc and SCSI connection.
(see above). Besides the modules for scanning color images, the
LinoColor suite available for the Topaz adds the CopixAssistant Imacon FlexTight Precision II Workflow:
Preview=> Correct=> Scan
and RegisterAssistant modules for use in copydot scanning.
Most of the comments for the QuickStep software apply also
to the Topaz.
Heidelberg Prepress Topaz IX
Pricing, sales and testing information. The Topaz is priced
at $36,000 for the standard version and $47,500 for the Topaz IX
without copydot software, which is available for an additional
$14,500. It is sold through Heidelberg Prepress’s normal distribution channels.
Our testing was done at the Kiel facility.
Like the bigger Eskoscan models, the 1318 is controlled by a PC
(a 500-MHz DEC Alpha is used for the 1318) running under NT
and equipped with a large, tabletop digitizing tablet. The operator
can therefore prepare images for the next batch while the first one
is being scanned. The digitizing tablet makes it possible to skip the
overview scan step in the capture process, although this is otherwise a necessary part of the scan. In fully automated mode, the
scanner operator doesn’t need to preview images, but can rely fully
on the software to analyze and adjust the images for gray balance
and highlight and shadow points.
Purup-Eskofot provides several templates with the scanner,
but users can easily produce templates of their own. The different
templates can be referenced when preparing a batch, so that all
cropping is done automatically. The Eskoscan is calibrated once at
installation for geometric accuracy, which ensures that the digital
seams are handled correctly. Weekly calibration compensates for
the aging of lamps, white balance and
variations in light intensity over the width
of the copyboard.
Imacon’s Color Flex control software, which runs on both the
Macintosh and the PC, provides a range of professional tools required by a skilled operator. The recently released PC version includes full ICM support. Despite its rich feature set, the software
is simple to use for less-skilled operators. It provides tools for batch
scanning, although the A4 format of the model we tested and the
capabilities of the image holders it supports limit batch scanning to
35mm slides and 120 film strips.
Although Color Flex is compliant
with ICC standards, Imacon takes a pragmatic approach to the ICC standard. It
recommends that the user stick to the
default ICC scanner profiles, rather than
trying to create better ones. Imacon
states that the scanners have such a stable
and linear behavior that a normal calibration of white point is enough to ensure color accuracy thereafter.
The procedure involves conducting
first an overview scan, then a preview scan
Purup-Eskofot’s Eskoscan 1318
16
Pricing, sales and testing information. The U.S. list price of $47,500 includes the scanner, workstation, digitizer
and all software. Without the workstation, the price is $41,500.
The test was performed on a 550MHz DEC Alpha Personal Workstation
with 64 MB of RAM, an ultrawide SCSI
link and a 4.3-GB hard disk.
ScanView’s ScanMate F8 Plus
ScanView’s ColorQuartet scanning and separation software, which is used with all of the
company’s drum and flatbed scanners and
digital cameras, is known for its professional
functionality and ease of use, even for lessskilled operators. It provides color manipulation and separation tools in addition to scanner
controls. It also includes modules for copydot
scanning and fully or semiautomatic scanning.
Functions address unsharp masking, black
generation (using a tone curve or numeric
controls), gray balance and tonal range adjustments, color cast corrections and calibration of the scanner.
ColorQuartet also provides a utility that recognizes the
punched-hole codes on a mounting plate to enable the scanner to
interrupt a batch scan with an urgent job. Rather than instructing
the scanner to restart the scan, the software remembers where it
was when the interruption took place, in either the preview or the
high-resolution scan.
One of ColorQuartet’s latest features, called “Mousefree”
scanning, improves workflow. The scanner crops, analyzes, names
and scans all the images in a template automatically, as soon as the
scanner’s lid is closed.
ColorQuartet is fully ICC-compatible. All color separation
tables can be modified within the software or by using a thirdparty ICC profile editor. ColorQuartet comes with a selection of
output profiles and allows the user to edit profiles created in other
programs.
All processes can be overlapped. The F8 Plus can scan while
the operator performs setups or corrections using the ColorQuartet
software.
Pricing, sales and testing information. The F8 Plus with
ColorQuartet software costs $33,495. The copydot scanning capability is an option, priced at $8,500.
At Ipex, ScanView demonstrated a new model, the F10, which
provides xy scanning technology and captures data at the maximum resolution of 5,400 ppi anywhere on the scan bed.
It is ICC-compliant and offers a wide
range of advanced functions for image analysis and correction. Other features include CMYK
and HSL color correction, a moiré-elimination
filter, UCR, GCR, UCA, sharpness and gradation
controls, detail control, “before” and “after”
split-image viewing, tonal range and sharpness editing using the Max Detail feature, and
two-point scaling. (Two-point scaling enables
the software to calculate the relative enlargement or reduction of an image, based on a
measurement of the distance between two
points within the image.)
The user interface includes a floating
densitometer, automatic image analysis and
the ability to select multiple sample points as
reference points for the setup. There is also a line-art mode and
copydot scanning function through the EverSmartDot software
(developed for the EverSmart Pro). This software, for copydot
scanning and digital descreening, supports a top optical resolution
of 2,540 dpi.
The control software incorporates a SmartSet module for
automatically modifying the scanning parameters for an image based
on a set of stored input categories such as “people,” “outdoor,”
“metal” and “still life.” There are two levels of complexity used in
capturing a group of images that are very similar. The second level
allows the operator to access the advanced settings and functions
in the software. Little operator attention is required.
The EverSmart Pro comes with a 30-hour, computer-based
training course comprising a CD-ROM, an exercise book and a selection of original images to scan. The course provides a basic introduction to color theory and color separation, as well as basic
and advanced scanning techniques.
Pricing, sales and testing information. The EverSmart Pro—
the middle scanner in the product line—sells for $34,950 (down
from a price of $39,950 when it was released), with the SmartDot
option adding $5,000.
Our tests were conducted at the National Exhibition Center
in Birmingham during the Ipex trade show, with a G3 Mac with
256 MB of RAM and a 24-GB hard disk.
ScanView ScanMate F8 Plus Workflow:
Auto Preview => Auto or manual crop => Auto or manual setup
and corrections => Batch, single or auto scan
Scitex EverSmart Pro Workflow:
Preview => Autocrop => Prescan => Correct => Batch or single scan
Scitex EverSmart Pro
Screen Cézanne
The EverSmart Pro’s control software runs on a PowerMac and
builds on the capabilities of Scitex’s earlier Smart 342 scanner. It
adds a layout feature to support the EverSmart Pro’s larger scan
area. It provides other features, including tools for batch functions
and background scanning, plus tools for intelligent setup and a
queue and preview browser.
The Cézanne incorporates the same artificial intelligence that Screen
developed for its 1045 A4 flatbed scanner and the large-format
8060 high-speed drum device. It provides intelligent setups and
additional functions for negative scanning (particularly applicable
to newspaper work). The AI software has an autolearning function
based on an evaluation of the statistics generated each time the
17
March 2, 1999
If software is written well and data are
transferred efficiently from the optical system
to the hard disk, it can make a distinct
difference in the overall results.
device scans. There is also support for 8- and 16-bit ICC output
profiles.
Images can be mounted either directly onto the scanning
bed or onto special image mounts containing image-recognition
markers that the Cézanne uses in setting scanning parameters.
Different image types can be mounted and scanned in a single
pass.
Screen also supplies a flexible cover suitable for batch scanning or for flattening images that can’t be taped, such as old or
damaged originals.
Artificial intelligence. The scanner automatically performs an
overview scan as soon as the lid is closed. The control software
then automatically identifies the different images, making a preliminary crop of each image. The application of artificial intelligence makes it possible for the scanner to use an operator’s inputs
for image analysis and image correction as the basis for corrections
to similar types of originals. In other words, the control software
learns with experience.
Screen has added significantly to their ColorScope Pro control software since it was introduced last year. This client-server
Macintosh program (both the client and server can run on the
same platform) is designed so that two users can work over an
Ethernet network sharing a single scanner. It allows the operator
to perform setups while the scanner is capturing data, although the
scanner will not actually scan while it is writing to disk, which is a
limitation in productivity.
To address copydot scanning, Screen recently added the Dot
Finder, which is incorporated within ColorScope Pro. During a
full-resolution copydot scan, the software uses stitching technology to knit the data stripes together.
Operating modes. The Cézanne’s control software has several
levels of operation, ranging from easy, highly automated controls
to fully manual controls for an experienced user.
The “intelligent” mode is the most highly automated, relying
on a very clear, simple-to-use graphical user interface and intuitive
keywords rather than technical descriptions. These keywords are
used to establish highlight and shadow points, color cast removal,
color correction, tone curve adjustments and USM. Thus, it is possible to use relatively nontechnical language to instruct the scanner
as to the type and look of an original, and the ideal output.
Scanner settings are linked to these keywords. So, for example,
a general scan with a “standard” setting will use standard values for
highlight and shadow settings. But a general scan with a “chinaware” setting will set a high white point and adjust sharpness for
smoother rendition of the surfaces. If autolearning mode is specified, the scanner will use AI to track all operations, building up a
history of setups and user preferences. This further enhances the
keyword functions.
In manual mode, all functions are controlled directly. It is
possible to use a combination of automatic controls and manual
fine adjustments. Thus, the effectiveness and efficiency of the software grow as the user gains experience. The autolearning mode
also can be used in this context.
18
ColorScope Pro supports ICC-compatible monitor and output profiles. Output can also be in Scitex CT, TIFF, EPS, DCS and
JPEG formats.
Pricing, sales and testing information. The Cézanne costs
$34,000. Our tests were done at Screen’s Milton Keynes facility in
the UK, using a G3 Macintosh with 256 MB of RAM.
Screen Cézanne Workflow:
Overview scan => Crop => Preview => Corrections => Batch/single scan
Evaluating the Test Results
In our last issue, we compared the productivity of these nine scanners. The other area that is critical in evaluating a scanner is the
quality of the results it achieves. That is the focus of the following
comments.
Defining quality. As we have suggested above, quality is much
more than a matter of a scanner’s optical resolution. Achieving
good-quality scans depends on the capabilities and precision of the
optical system as well as the scanner’s control software. The software, including its power, feature set and user interface design, can
enhance the results considerably to compensate for limitations in
the optical system.
An important point to keep in mind regarding quality is that
the scanner must produce consistent results across a range of image
types and for a wide variety of requirements, such as enlargement
factors.
Another important point to remember is that quality and
productivity can sometimes be traded off to increase one or the
other. In other words, quality may be sacrificed to increase speed,
or speed may be sacrificed to enhance quality. To some extent, this
is an issue of data management, but, if software is written well and
data are transferred efficiently from the optical system to the hard
disk, it can make a distinct difference in the overall results.
These were some of the considerations we pondered as we
designed the tests and evaluated the results. We recognize, though,
that in the end the final arbiter is what the eye perceives in print.
Our observations follow.
(continued on p. 23)
About the Color Insert
The following four pages contain color samples printed from
actual scans from the scanners reviewed in this article. Where
possible, we have provided comparable samples for all nine
scanners, and we have tried to select samples that demonstrate the points raised in our evaluation. To obtain a more
comprehensive set of samples, see the box “Pixel Perfect: A
Buyers’ Guide” at the end of this article.
color insert
19
March 2, 1999
color insert
20
color insert
21
March 2, 1999
color insert
22
The 4×5-inch transparency test contains a
wide range of textures and colors, and
includes complex fine details in both light
areas and dark shadows.
(continued from p. 18)
What to look for in transparency scans
Prior to the test, scanner operators were given basic information
about the likely printing conditions, but they were not allowed to
“rehearse” any of the tests. We advised all scanner operators that
we would use positive film and plates and that we anticipated approximately 4% dot loss when imaging film to plates and approximately 19% dot gain on press. We expected 340% total ink coverage
when setting up the scan parameters.
For each proof of a scanned image, we looked specifically at
color accuracy and depth, gray balance, overall sharpness and rendering of fine details, and highlight and shadow rendering. Each
scanner was given a score of between one and ten for each of
these five criteria. We then averaged the five scores to obtain a
single figure for each device. We have included annotations where
relevant.
The following commentary on what we were looking for and
what we found as we evaluated the scans of the transparencies may
help you understand our conclusions and, perhaps, draw conclusions of your own.
The 4×5-inch transparency test
We selected this first-generation image from Kodak for several reasons. It contains a wide range of textures and colors, and includes
complex fine details in both light areas, such as the watch face, and
dark shadows, such as the fabric patterns. The image also covers a
wide density range with very light areas, such as the shirt, and very
dark shadows, such as can be seen beneath the bolts of fabric.
Of course, it is virtually impossible to make an absolute evaluation of the quality of a printed image before it is printed. Since we
had to write this commentary prior to seeing the printed images,
we felt that the best way to come close to seeing a printed image
would be to generate a high-quality proof as the basis for our analysis. With that in mind, we produced Cromalins of the 4×5-inch
transparency that was scanned by each participating scanner.
We were looking for the overall quality of the scanned image
and the accuracy with which the Cromalin matched the original
transparency. In particular:
• Saturation and color consistency. We looked at color saturation
to see if there was a tendency to under- or oversaturate colors,
plus the overall color balance and consistency of rendering color
across large highlight and shadow areas. The blue and red handkerchiefs are particularly telling for both saturation and consistency, since both include subtle color transitions within their
folds and shadows. On the original, these colors are extremely
vibrant, a characteristic we had hoped to see in the scans.
• Gray balance. The hat and some of the fabrics provided a useful
means of comparing gray balance and color saturation. We hope
this will be visible in these pages, which ranged in color from
gray to green. (On the transparency, the hat is gray, tending
toward blue, rather than green or black.)
• Contrast. We were interested to see how well the scanner captured subtle color contrasts, both in the shadow and highlight
areas. Where there are relatively large areas of similar tones, such
as in the handkerchiefs and the white shirt, we paid particular
attention and found them revealing. The white ranged from a
“grubby” gray to pink on the proofs.
• Detail. Small texture renditions also served as a basis for comparison. We looked for edge detail rendering, particularly in the
watch face, the feathers in the hat and the cotton reels. The
sharpness and general accuracy of details throughout a textured
area provided a useful guide to consistency in fine detail rendering. The fabric patterns also were useful in this respect, as well
as to show any tendency toward moiré. We were interested in
how well the devices with a high maximum density would render color—in particular, whether we would see better shadow
detail and finer highlights.
How the players fared
Here are the results of our evaluation of quality of the scans of the
4×5-inch transparency. All of the scanners did a creditable job;
some were outstanding.
Agfa AgfaScan T5000. Although the T5000 is a relatively lowcost device, we felt that it yielded more than acceptable results for
a scanner in this price bracket. Its good rendering of very dark
shadows unfortunately compromised the highlight areas, but color
accuracy, color depth and gray balance were consistent, producing
a commendable result.
Color accuracy
Color depth
Gray balance
Overall sharpness
Highlight and shadow rendering
Average score
6
6
6
6
7
6.2
Fuji Lanovia C-550. The C-550 produced excellent overall
results. Our criticisms were that the highlights were too dark, there
was some loss of shadow detail and a red cast was evident in several
areas, most notably in the white shirt. But, overall, we were impressed.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
8
8
6
8
7
7.4
Heidelberg QuickStep. We didn’t expect great results from this
scanner, knowing that it is at the low end on the price scale, and
it lacks the optical sophistication of some of the other devices included in the test; however, we were pleasantly surprised. The results were commendable. Our biggest criticism was an overall
washed-out appearance, with very light shadow rendering and a
23
March 2, 1999
Zooming alone doesn’t allow the capture of
the full resolution across the entire scan bed,
which is imperative for copydot scanning.
About XY Scanning, Zooming and Stitching
There is much debate within the vendor and user communities
concerning the need for or utility of xy scanning. Its advocates
claim that it enhances performance and quality, particularly when
gang scanning a large number of originals. In doing so, it breaks
the bond between the maximum enlargement and the size of
the CCD array, enabling the scanner to capture data at its highest resolution anywhere on the scan bed.
ning at the exact resolution required, rather than in steps, as in
the case with fixed lenses and which subsequently requires either
downsampling or interpolation to yield the desired output resolution. The zoom systems used in the Fuji Lanovia C-550 and
the Screen Cézanne, for example, are claimed to provide greater
flexibility when it is necessary to adjust for specific enlargement
factors and output resolutions.
In conventional scanning, the CCD array travels in one direction
only (the x direction), and light is focused onto it via a lens or
lenses. A CCD array is a light-sensitive, integrated circuit with an
array of photosensitive sites on which an electronic charge builds
up according to the length of the exposure of each site to light.
With conventional scanning, the lens is centered on the middle
of the scan bed. At low magnifications, the whole bed can be
scanned, but, at higher magnifications, only a central strip is
focused on the CCD array. Xy scanning repositions the scanner
optics relative to the target image for both the x and y directions, rather than the single direction of conventional scanners.
This permits the scanning, at high resolution, of strips on either
side of the central area of the bed.
Stitching and copydot scanning. Zooming alone, however,
doesn’t allow the capture of the full resolution across the entire
scan bed, which is imperative for copydot scanning. To digitize
complete films at full resolution requires stitching, and both the
C-550 and the Cézanne, use stitching technology when
performing copydot scans, although they don’t stitch when scanning color images.
The theory goes that the xy technique also provides uniform
quality throughout the scan for both single images and multiple images positioned anywhere on the scanner bed. These
images can still be enlarged to the maximum limit, so multiple,
high-enlargement, quality scans can be made simultaneously.
Zooming. XY technology can be used in conjunction with one
or two additional technologies: zoom (in which case the complete technology is sometimes referred to as xyz scanning) and
stitching. With a zoom system, a zoom lens moves to focus the
target image data across the entire width of the CCD, thereby
yielding the desired resolution up to the maximum of the CCD
array’s width. Zoom systems have the added benefit of scan-
Selected Scanner Features
Scanner
Agfa AgfaScan T5000
Fuji Lanovia C-550
XY-capable
✓
✓
✓
3
✓
✓
✓
24
Zoom lens Fixed lenses
✓
Screen Cézanne
✓
✓
2
There is no need to stitch if an image falls within the width of
the CCD array, but, if it is wider than the CCD, the optical system
must make more than one pass over the image, and the scanned
data must then be stitched into a composite whole. It’s rather
like the electronic equivalent of pasting together sheets of
wallpaper so that there are no signs of a join.
The digital data swathes have to be matched up and the edges
analyzed to ensure that no data are introduced that could constitute visible artifacts. Solutions to this problem range from
edge recognition techniques to special algorithms that analyze
a complete scan to ensure that none of the joins can be seen.
This matching requires that the scanner recognizes what constitutes an edge or not, and that it can distinguish the discrete
points along these edges precisely, without creating gaps or
overlaps.
Added to the problem of accurate edge recognition is the requirement of graphics scanning to match up the three filtered
colors of red, green and blue data. The stitching
software must be able to align three sets of data
stripes both side to side and layer upon layer.
Stitching
There also is the need to recalibrate the system
between swathes, which can result in a time pencopydot only
alty, depending on the speed of the mechanism.
There also is a question of vulnerability of the
optical system to calibration problems.
✓
✓
1
✓
✓
copydot only
Scanning systems that offer stitching invoke it
only when necessary, such as when scanning
large originals at high resolution. This isn’t often
required, however, and, when it isn’t required,
the desired output resolution is obtained via the
zoom setting or computation through
downsampling or interpolation.
The Topaz colors were vibrant and lively, and the
rendering of highlight and shadow areas was
excellent. The Cézanne colors were rich, and blues
and reds were almost as gorgeous as in the original.
yellow cast, which is consistent with the scanner’s
relatively limited density range of 3.4.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
5
5
5
5
7
5.4
Heidelberg Topaz. The Topaz was one of the
most impressive of the scanners on this image. The
colors were vibrant and lively, and the rendering of
both highlight and shadow areas was excellent.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
7
8
6
8
9
7.6
Quality evaluations (4×5-inch transparency, 250% enlargement)
Agfa AgfaScan T5000
6
6
6
6
7
6.2
Fuji Lanovia C-550
8
8
6
8
7
7.4
5
5
5
5
7
5.4
7
8
6
8
9
7.6
7
7
5
5
6
6.0
6
6
7
6
8
6.6
Scanview ScanMate F8 Plus
5
5
5
6
6
5.4
7
6
8
8
9
7.6
Screen Cézanne
7
8
7
9
9
8.0
Imacon FlexTight Precision II. One of the less expensive
models, the FlexTight Precision II is marketed as a low-cost scanner that yields high-quality results. We found that, although it performed relatively well in terms of color accuracy and color depth,
it tended toward oversaturation of color, with the result that highlights and shadows were too dark and lost detail. There also was a
red cast to the image.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
7
7
5
5
6
6.0
Purup-Eskofot Eskoscan 1318. The Eskoscan 1318 results
were only average, making it perhaps the most disappointing performer in this series, given its premium price. Blues were dull and
the color rendering in general was rather flat. However, it did render highlight and shadow details well, despite a comparatively low
density maximum and narrow density range.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
6
6
7
6
8
6.6
ScanView ScanMate F8 Plus. The F8 Plus produced adequate
results, although the overall image was flat and had a red cast. The
color accuracy, depth and gray balance were all disappointing, and
there was insufficient definition, particularly in the watch face.
Color accuracy
Color depth
Gray balance
Overall sharpness
5
5
5
6
Color
Color Gray
Overall Highlight/ Average
Accuracy Depth Balance Sharpness Shadow
Score
Scanner
Average score
6
5.4
Scitex EverSmart Pro. The EverSmart results were excellent,
with good rendering of fine detail and gray balance. However,
although overall the colors looked strong, we weren’t so impressed
with the color depth, particularly in the silk handkerchiefs, where
there was loss of subtlety in tonal shades.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
7
6
8
8
9
7.6
Screen Cézanne. The Cézanne results were outstanding on this
image. Colors were rich, and the intensities of the blues and reds
were almost as gorgeous in the scanned image as in the original.
The Cézanne may be slow (see productivity comments in Part I of
this study), but the results in this part of the test support the considerable success Screen has had with this scanner.
Color accuracy
Color depth
Gray balance
Overall sharpness
Average score
7
8
7
9
9
8.0
The xy factor
Perhaps the most interesting aspect of the evaluation process was
the performance of the new generation of devices that employ xy
technology compared with the conventional technologies.
One of the claims of the xy devices is that they are more productive because they permit gang scanning of greater numbers of
originals at one time at high resolution. This argument, although
25
March 2, 1999
Some of what appeared to us in the Cromalins
and on the screen may not be apparent in
print. The printed versions might not show the
same color saturation and color casts.
it makes sense in theory, didn’t hold true in our testing, illustrating
that productivity is a function of more than just the number of
originals that can be scanned at one time.
Who does and who doesn’t. Of the nine scanners in our tests,
four offer the option of xy scanning in a gang-scanning situation:
the EverSmart Pro, the Cézanne, the Lanovia C-550 and the
Eskoscan 1318. Not supporting xy technology are the AgfaScan
T5000, the FlexTight Precision II, the QuickStep, the Topaz
and the ScanMate F8 Plus. Since our testing, ScanView and Agfa
have added xy models to their lines (the ScanView F10 and Agfa
XY-15, which is built around Agfa software and a version of the
Fuji Lanovia hardware). That leaves only Heidelberg and Imacon
without xy devices.
And does it matter? Because the xy scanners tend to be relatively expensive, one of the questions we wanted to answer was
whether the extra capability they offer is worth the price. Stated
another way, we wondered whether the lack of ability to scan at
full resolution across the entire scan width could be offset by the
lower prices of the T5000, FlexTight and F8 Plus. After completing the tests, we felt that such an argument might plausibly be
made for the T5000 and the FlexTight, but that it would be harder
to do so with the F8 Plus.
Ultimately, value for money depends on the specific needs of
a purchaser and consequently is very difficult to test. It is important, however, for buyers to consider the tradeoff between the quality
produced by these scanners and the prices charged for them, taking into account the users’ own applications and opinions of the
results.
Given the high price tag of the Topaz, we wondered whether
our results would indeed confirm Heidelberg’s argument that conventional flatbed scanning technology can yield just as accurate and
pleasing a result as xy technology, even if the xy device combines
zoom technology and stitching with the xy movement. Comparing
the results of the Topaz with those of the Eskoscan 1318, its closest
xy-stitching competitor in price, suggests that the results confirm
Heidelberg’s view.
However, compared with the EverSmart Pro, the Cézanne and
the C-550, the argument is perhaps not as strong, particularly since
these scanners are all less expensive than the Topaz.
Proof vs. print. In basing our commentary on the proofs of the
images, rather than prints taken from an offset press, we are aware
that some of what appeared to us in the Cromalins and on the
screen may not be apparent in print. The printed versions might
not show the same color saturation and color casts as are apparent
on the Cromalins, which have a lower dynamic range than the
original image but also have a higher range than the final print.
For this reason, we emphasize that the reader will have to
make the final judgment about the printed samples bound into
this article.
Optical resolution and interpolation
We tested optical resolution using a glass Variable Frequency Resolution Target. Our primary intent was to see whether each scanner
achieved the resolution given in its technical specifications. We also
wanted to see what additional benefit, if any, interpolation software might provide.
Optical resolution. This evaluation turned out to be more difficult than we expected. The target is designed to measure the
spatial frequency of black and white transitions, using parallel lines
with increasingly tight spacing. As the lines get finer and finer, and
the spacing gets tighter and tighter, the difference between lines
and spaces becomes more difficult for the scanning optics to resolve. Eventually, the optical system will record only gray, which
means that the limit of optical resolution has been exceeded.
We based our judgments of these scans primarily on what was
visible on-screen when we viewed them at high enlargement. We
looked for detectable light/dark transitions. We tried to establish
the point at which the line pairs approached uniform gray with no
modulation visible.
Our task was complicated by the moiré patterns that are evident throughout these scans (and which can no doubt be seen in
the printed samples). The moiré is caused by interference between
the frequency of the lines and the scanning resolution. It is not
relevant and can be ignored, as long as the transitions from light
to dark and back are visible.
Once we had agreed on the point at which no lines were
visible, we calculated the resolution in pixels per inch as follows:
resolution = 2 × (lp/mm) × 25.4
Wanted: New Slide
During the course of these tests, our 4×5-inch transparency sustained a scratch. Our original had been kindly
supplied by David McDowell at Eastman Kodak, but,
unfortunately, Kodak no longer handles it. If any reader
has one of these images, we would be pleased to hear
of it, with a view toward using it when we test some
newly introduced, high-end flatbed scanners. Please contact Paul Lindstrom: [email protected].
26
where “lp/mm” is the maximum number of line pairs per millimeter we were able to discern.
We conclude that the optical resolution stated in most scanners’ technical specifications is slightly over-optimistic in practice.
The exception was Screen’s Cézanne, which actually exceeded its
claimed resolution.
Interpolation. Another important objective of these tests was to
evaluate the role of interpolation in enhancing image detail. As can
be seen from these results, interpolation can provide a useful service. It can be used to increase the number of pixels in the output
file, either to avoid moiré or to achieve the desired output resolution; however, it cannot provide additional image detail.
The scanner manufacturers specify much
higher interpolated resolutions, but our tests
confirm that no additional image detail is
obtained.
Claimed vs. Measured Resolution of High-End Flatbed Scanners
Scanner
Agfa AgfaScan T5000 (width)
Agfa AgfaScan T5000 (height)
Fuji Lanovia C-550
(line art scan)
Screen Cézanne
Claimed optical resolution
Specified
Equivalent
as PPI
in lp/mm
2500
49
5000
98
5000
98
2400
47
5080
100
7620
150
5760
5080
4000
3175
5300
113
100
79
63
104
Measured values (line pairs/mm)
Horizontal
Vertical
non-interp.
interpolated
non-interp.
interpolated
55
45
[Not tested. Fuji lab sample files: about 90 lp/mm]
45
45
45
50
95
85
95
95
120+
120+
[Not tested. Device cannot scan rigid glass resolution target.]
95
95
90
85
75
70
70
75
50
55
55
50
100
120
100
120
Our measurements of interpolated data showed that, in general, the maximum resolution was essentially the same as the noninterpolated scans. The scanner manufacturers specify much higher
interpolated resolutions, but our tests confirm that no additional
image detail is obtained.
There were two interesting exceptions: the Scitex EverSmart
Pro (which fell short of its specified resolution when scanning at its
claimed maximum, but did better when interpolating), and the
Screen Cézanne (which provided better-than-specified resolution
when interpolating). The detailed results follow.
Agfa AgfaScan T5000. Agfa did not submit a separate interpolation test. The result shows that the T5000 should be considered
to have a general maximum optical resolution of around 2,500 ppi
(the manufacturer’s stated horizontal resolution). The ability to
scan at 5,000 ppi in the vertical direction did not seem to contribute to the measured resolution.
Fuji Lanovia C-550. Fuji chose not to submit the results of its
tests. Instead, Fuji ran the tests in its labs and submitted a result
that demonstrates the capabilities of the Lanovia’s optical system.
This result was obtained with some changes to the scanner’s control software (specifically, switching off the grain filter).
Fuji explained that the Lanovia is designed primarily for film
scanning and therefore would not be able to produce acceptable
results scanning a glass platen, without some software modification.
Another difficulty arose from the fact that the C-Scan software
does not allow the user to specify the desired scan resolution. In
what may be a hangover from past practices, this software requires
the user to specify the desired output resolution and enlargement
factor, calculating the scan resolution accordingly in software.
Fuji’s scan shows modulation up to 90 lp/mm using interpolation. This has been achieved in the Fuji labs under controlled conditions, and not in the same way as the other test
participants.
Measured
vs. claimed
112%
46%
95%
95%
95%
95%
88%
96%
Heidelberg QuickStep. This result is exactly at the claimed optical resolution, and using interpolation did not increase it.
Heidelberg Topaz. The tested horizontal resolution comes close
to the claimed resolution. The vertical resolution seems to be slightly
lower. Interpolation did not change the tested numbers.
Heidelberg Topaz IX. We preferred to scan the glass resolution
target in gray-scale mode. But, on the Topaz IX, the target was
scanned as line art, since this is the mode in which the 12,000element monolinear array is used. Although we found the scans
difficult to evaluate precisely, it is clear that the 12,000-element
array does raise the resolution of Topaz IX.
Imacon FlexTight Precision II. It is not possible to scan
rigid media with this scanner, so Imacon could not complete this
test and we cannot confirm the manufacturer’s resolution claims.
On the other hand, we did find that film grain is clearly reproduced on a 5,760-ppi crop of a high-resolution scan, which indicates that the Imacon scanner’s resolution is probably close to
the claimed level.
Purup-Eskofot Eskoscan 1318. The measured horizontal resolution comes very close to that claimed by the manufacturer, although the vertical resolution is somewhat less. Interpolation did
not improve the results.
ScanView ScanMate F8 Plus. The horizontal resolution is close
to the manufacturer’s claim, and the vertical is slightly lower. Once
again, interpolation does not improve the results.
Scitex EverSmart Pro. We were surprised by the difference
between the manufacturer’s specifications and the measured results
for the EverSmart Pro. After the test, we were told that requesting
a scan at 3,175 ppi (the claimed resolution) doesn’t change the
27
March 2, 1999
Attention to data-flow issues is important when
working with the large files these scanners produce.
We noticed performance differences from such things
as not closing other applications during scanning.
lens position from the normal 2,500 ppi. The switch to 3,175 ppi
occurs only when a resolution higher than 3,175 is requested. This,
we were told, explains why the scan using interpolation shows a
slightly higher measured resolution (although this, too, was short
of the claimed 3,175 ppi).
Screen Cézanne. The Cézanne’s result comes very close to the
figures stated in the specifications. In this case, however, the interpolated result is even better, with lines visible at 120 lp/mm—
beyond the manufacturer’s claimed resolution. This is surprising,
and it differs from the results with the other scanners.
Summary of resolution-testing results
For the most part, our testing confirms the resolution claims made
by the manufacturers. Most scanners performed very close to their
specifications. The Scitex EverSmart Pro fell somewhat short (but
only by a matter of about 15%), and this result may be related to
a quirk of the scanning software. More surprising is the unexplained
fact that the Screen Cézanne exceeded its resolution specifications,
at least when interpolating.
Conclusion
Our goal in this project has been to provide an objective evaluation of the current range of high-end flatbed scanners on the market.
We hope we have achieved this in a way that is meaningful to
prospective purchasers and users of this technology.
It is interesting that there was no clear winner of all of the
tests; different devices excelled in different tests. For example, the
tests showed that Scitex’s EverSmart Pro offers the most compelling combination of speed and quality, followed closely by the
Heidelberg Topaz and Fuji Lanovia C-550, which are nearly equivalent in these terms. On the other hand, the Cézanne performed
the best in the area of quality, but its overall attractiveness is com-
Pixel Perfect: A Buyers’ Guide to
High-End Flatbed Scanners
This article contains a subset of a more comprehensive
study performed by Paul Lindström and Laurel Brunner.
The full results, with several pages of output samples for
each tested scanner, are contained in a separate publication called “Pixel Perfect: A Buyers’ Guide to High-End
Flatbed Scanners.” The Buyers’ Guide can be obtained
for $40 from Seybold Publications at 610-565-2480.
Subscribers to The Seybold Report on Publishing Systems
can obtain a substantial discount.
28
promised by its slowness. Ultimately, therefore, we don’t believe it
would be fair to declare an overall winner in this project; the diversity in approaches and innovativeness in this field make such a
declaration impossible.
The following table summarizes the results of the testing. We
hope readers will find this useful as a basis for assessing the compromises when comparing devices:
Overall Ratings
Agfa AgfaScan T5000
Fuji Lanovia C-550
Heidelberg QuickStep
Heidelberg Topaz
Screen Cézanne
Productivity
7.54
8.45
5.48
8.35
7.10
5.33
9.67
8.99
3.82
Quality
6.2
7.4
5.4
7.6
6.0
6.6
5.4
7.6
8.0
Quality issues. Besides the differences among these devices in
terms of technology, image quality and productivity, we have learned
a number of things from this project.
Ideally, a scanner should provide high resolution and a wide
dynamic range, but these specifications alone cannot be used as
indicators of performance. They must be considered in the context
of factors such as software efficiency and ease of use.
Our tests confirmed that we are at or near the upper limit of
useful resolution with the present crop of scanners. Scanning resolutions above about 5,000 pixels per inch, even with an original on
high-quality film, will serve only to record more clearly the film
grain.
Performance. Attention to data-flow issues is particularly important when working with the large files these scanners produce. The
processes of scanning, data transfer and writing to disk need to
occur in parallel. Although the front-end system may support background operation, scanning and writing of data may not occur
simultaneously, and this can clearly hurt performance in volumescanning environments.
The user, as well as the manufacturer, must pay attention to
these performance issues. We noticed performance differences arising from such things as not closing other applications during
scanning, or not turning off unnecessary system extensions. And
disk fragmentation is critical: We observed one case where a scan
took 45 minutes prior to defragmentation, but only 26 minutes
afterward.
To be continued. An interesting area for further exploration is
the practical value of density range and maximum density specifications. High values are not always associated with high quality, as
our tests have shown. But are a big range and a high maximum
valuable? For what kinds of work? We are considering a future
round of testing in which density specifications would be put to a
practical test.
Laurel Brunner with Paul Lindström

Concluding a Two-Part Study Testing the Scanning Quality Of Nine

Transcription

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