Chris Tuijn

Transcription

Chris Tuijn

Agfa
Chris Tuijn
[email protected]
Tuijn
Köln, May 19, 1999
Agfa Lectures - Fachhochschule Köln
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Introduction (Agfa organization, DTP …)
● Some hardware background of input devices
●
– sensors
– scanners
– digital cameras
Image processing of digital images
● Applications
● Conclusions
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Graphic Systems Division
Conventional Pre-Press Systems
● Electronic Pre-Press Systems
● Output Systems Division
●
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Technical Imaging
Medical Division
● NDT (Non Destructive Testing)
●
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Consumer Imaging
Foto Division
● DTP
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Focus on the home/office user
● Products:
●
– CCD scanners
home/office (SnapScan scanners)
● publish scanners (DuoScan scanners)
●
– Digital cameras
ePhoto 780, 1080, 1280, 1680
● CL30, CL50 …
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Software Development
– Development of applications for different markets:
Home
● Office
● Publish Environment
●
– Applications for different input devices:
Scanners
● Digital cameras
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The application development consists of several
layers:
– Image processing and Color management library
– Engine interfacing layer (cf. Scan Server)
– Application development
Common layer for different platform
● UI-dependent part (Windows, MacOS)
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Communication
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Application
Color Image Enhancement
Color Image Restoration
Engine Interfacing
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CMS/IMS Library
– CMS: Color Management System
●
guarantees reliable color across different devices
– IMS: Image processing component
spatial image processing such as sharpening,
noise removal, resolution enhancement …
● automatic color correction
● negative scanning
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Scan Server
– Multi-platform library which takes care of
Engine interfacing
● Image processing and color management
● multi- and parallel processing
●
– Provides an abstract a-synchronous
communication channel with clients over:
in-memory bus
● TCP/IP ...
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Application Development
– Multi-platform kernel, based on objectoriented design
– User Interface part which is developed in the
native platform specific UI libraries:
MSVC++ with MFC (Microsoft Foundation
Classes)
● PowerPlant on the Macintosh
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Some hardware background on input devices
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Sensors
– CCD’s
– CMOS technology
Scanners
● Digital cameras
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The heart of the input devices
● Convert light-energy (photons) into electrical
energy (electrons)
● Two main technologies are used today:
●
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– CCD’s (charge coupled devices)
– CMOS technology
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Collectors are ordered line-wise
● The collectors build up a charge after exposure
and the charges are shifted line-wise using shiftregisters.
● In case of matrix CCD’s, the horizontally
shifted charges are, again, shifted out vertically.
● Then, they are fed to an ADC for discretization.
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Charge collection combined with electronics on the
same chip.
● Two versions:
●
– passive CMOS
– active CMOS: ADC, amps, processing hardware on-board
bigger dynamic range
● less noise
● fill factor: about 25 %
● faster processing (than CCD’s)
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Consist of several components :
–
–
–
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light source (lamp)
light-sensitive sensors
optical system that conveys light to sensors
electronics :
ADC (analog to digital conversion)
● image processing (hardware of firm-ware)
● interfacing layer (SCSI, Fireware, USB, …)
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There are 2 classes of scanners :
– PMT-based technology (photo multipliers)
●
drum scanners
– CCD-based technology (charged coupled
devices)
flat-bed scanners
● using filter-wheel or coated CCD’s (trilinear
CCD’s)
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Most cameras today still use CCD
technology.
● Different types of CCD’s:
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– Moving CCD’s
higher resolutions
● for still objects
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– Matrix CCD’s (lower resolutions)
lower resolutions
● “immediate” snap-shot
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Some quality issues
● Image restoration
● Image reconstruction
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Limitations of cameras:
– sampling problems
– problems related to CCD’s and CFA’s
(CFA = Color Filter Array)
– dynamic range problems
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User/scene related problems
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– problems with illumination
– high-frequency patterns in original scene
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Improve image quality
● “Reconstruct or recover an image that has been
degraded by using some a priori knowledge of the
degradation phenomenon” (Gonzales-Wintz)
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Color plane interpolation
● Color fringe removal
● Noise filtering
● Compression artifact removal
● Color management
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Single CCD detector
● Subsampling in three color planes
● Subsequently interpolating to reconstruct
three full-resolution color planes
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Simple interpolation
– Nearest neighbor
– Bilinear interpolation
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Methods using correlation of the different planes
Methods based on interpolation in HSL space
(smooth hue transition)
Techniques based on edge detection
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Sometimes, the signal/noise ratio is causing
bad images (typically in blue channel)
● Solution:
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– Mean filters
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fast, but filters out high frequency information
– Median filters
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slower, better than ordinary mean filters
– Adaptive mean filters:
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filter noise very well, preserves edges
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JPEG compression works tile-based
(typically on a 8x8 tiles).
● For high compression ratios, discontinuities
at the tile-boundaries become visible.
● These artifacts can be removed by spatial
filtering.
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Color management can be regarded as a
restoration, since the incoming signal is distorted
(recorded through an optical system and then
digitized).
● Problems:
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– unknown illumination
– color appearance problems
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Specification of the signal space using ICC
profiles.
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This class of filters will improve the images and
make them more pleasing.
● The deficiencies to be corrected are user and/or
scene-related.
● Two families of corrections can be considered:
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– color-based corrections
– spatial filters
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resolution enhancement
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Often, there is a mismatch in the tonality of the
original scene and the optimal digital representation
– over-exposed scenes (flash-light, sun)
– dark scenes
Sometimes, some specific areas need tonal
enhancement to show details.
● Problem with tonal corrections in general: can
cause posterization (8 bpp)
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Two types of tonal corrections can be
considered:
– global tonal corrections (look-up tables are
applied on R, G and B)
– selective tonal enhancements
masking
● dodging
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Color cast removal:
– The eye adapts chromatically but a digital camera
does not.
– detection of the illumination (can be combined with
color management)
flash-light
● sun
● other standard light-sources (Tungsten, …)
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Near neutral correction:
– this correction is often realized with a selective
color correction.
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Selective color corrections
– detection of common areas in pictures
sky
● grass
● skin-tone
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Non-optimal sampling because of
resolution limitations
● The human eye is sensitive to staircasing
● Solution : detect objects in scene and
reconstruct edges
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There are different approaches to this problem.
● Global techniques:
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– subdivide image in tiles of, say, 16x16
– model the image analytically (using regression
techniques from Numerical Analysis)
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birational splines (to preserve edges)
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– evaluate the pixels again
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Local techniques
– Using neural networks
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the training sets consist of patterns occurring in
small kernels
– Using rule-based systems with ad-hoc
heuristics
gradient based assumptions
● detection of patterns (edges, corners)
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Scanners
● Digital Cameras
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Different market segments need different
applications.
– Home/office: ScanWise
– Publish: FotoLook
– Pre-press: ColorExact
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Workflow can differ considerably.
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General workflow
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– Crop scan
– Automatic detection of the originals
– Analysis of the originals + automatic
correction and visualization (preview editing)
– Editing facilities
– Final scan (to disk, to other applications …)
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The user’s expectations
– Optimal quality with minimal user
intervention
– Easy work-flow:
easy manipulation of digital camera and/or
software
● downloading images should be intuitive
● print services over the Internet
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In the application, a photo album concept
is needed.
● Also support for voice annotation
becomes more and more important.
● Various file formats should be supported:
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– JPEG, TIFF, FPX
– DPOF: containing printing directives
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In the future: elimination of the workstation
● New trends:
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– JetSend
– Standardization of embedded OS’es
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DigitaOS, Windows CE, Embedded JAVA
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– Internet Imaging standards: IIP, JINI
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All digital input devices have their limitations.
● The firmware and/or software should achieve the
best quality possible (color management, image
processing).
● The end-user needs a good application to interface
with the input devices:
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– suited to the needs and the market segment
– easy to use, and yet sophisticated enough.
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Chris Tuijn

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