i Primatte Software Keyer Plug

Primatte
Software Keyer Plug-in Reference
Plug-in Release 3.0
for Primatte V5
Notice
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responsibility for the accuracy of the
information contained herein and
reserves the right to change the
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document. Please quote the revision
status of this manual when reordering.
This Document is Revision “B”.
Copyright © Quantel Ltd 2011
i
Notices
Trade Marks
Most of the product names mentioned in this manual are manufacturer
trademarks and are used within this manual only for the purpose of
identification.
Quantel iQ and Quantel QEffects are trademarks of Quantel Limited.
Primatte is distributed and licensed by Photron USA, Inc., San Diego, CA, USA Primatte was developed by IMAGICA DIGIX Inc., Tokyo, Japan Primatte is a trademark of IMAGICA DIGIX Inc., Tokyo, Japan ii
About This Manual
The information for this manual was written by Scott Gross of Photron USA, Inc:
3113 Woodleigh Lane
Cameron Park, CA 95682
Phone: 1-530-677-9980
Fax: 1-530-677-9981
Mobile: 1-530-613-3212
E-mail: [email protected]
URL: http://www.primatte.com
Skype: scottagross
This manual was revised for Quantel by Barry Hicks of Video Design
Software (VDS), and published by the Quantel Technical Publications
Department.
This is a change controlled document. Each page of this document is given
an issue letter (shown at the bottom of each page with the drawing number
and revision date) which represents the status of the page. Revision A on
any page indicates that the page is the original.
Any changes to any pages will raise the revision status of the document.
When re-ordering, always quote the document type, the documents number
and revision status along with the unit’s serial number:
B 02/11 XXXXXX Release 3.0 All pages
iii
Contents
Keying Using the Primatte Software Plug-in
Using the Primatte Software Keyer Plug-in
2
General Menu Operation
Selecting the Primatte Plug-in
Configuration Buttons
Hybrid Rendering (new in Primatte V5)
Key Mode Selection
Select BG (Key) Color
Cleaning Foreground & Background
Removing Color Spill
Spill Process Functions
Fine Tuning the Composite
Make Foreground Transparent
Restore Detail
Spill Sampling Tools
Matte Sampling Tools
Detail Sampling Tools
Adjust Buttons
Adjust Lighting Buttons (new in Primatte V5)
Auto Compute
Rendering the Whole Clip
2
3
4
10
11
12
13
15
15
18
19
20
20
20
20
21
25
27
28
More about the Primatte Algorithms
The Primatte Algorithm
Explanation of how Primatte RT+ works
Explanation of how Primatte RT works
28
29
35
36
iv
Primatte
Software Keyer Plug-in Reference
Keying Using the Primatte Software Plug-in
1
Using the Primatte Software Keyer Plug-in
General Menu Operation
Quantel offers two Primatte plug-ins, a Hardware Assisted Keyer Plug-in,
(found under the “Key” menu in QEffects), and a Software Keyer Plug-in,
found under the “QPlugin” menu (also in QEffects). The Hardware Assisted
Keyer Plug-in, discussed in a separate document, has faster performance,
but fewer features and lower precision than the Software Keyer Plug-in.
The Software Keyer Plug-in, discussed in this reference manual, offers
Primatte’s full feature set and precision, but renders in software and thus
may have slower performance.
The screen shot below shows the QEffects menu when QPlugin is enabled
and the Primatte Software Keyer Plug-in is selected.
When the Primatte Software Keyer plug-in is selected, the menu area at the bottom
of the screen displays keying menus while the desktop provides a visual
representation of the keying process being performed at the current frame position
in the clip. The above screen shot shows a blue screen image, and this document
uses the term “blue screen” throughout. However, the foreground image could just
as easily utilize another key color, for example, green screen.
See the “Plugins” chapter in the QEffects Application Reference for further details on
general QPlugin operation.
2
Selecting the Primatte Software Keyer Plug-in
Use the Primatte Software Keyer Plug-in to key out areas of a specific color
(usually blue or green screen) in the current layer, a “foreground” image or clip.
To apply the Primatte Software Keyer Plug-in to the current layer, turn on the
“Qplugin” button (to the far left of the QEffects menu under “Text”). Use the blue
list box button immediately under “Favourites” to select “Imagica” as the Plugin
Producer .Then in the blue list box immediately below, select “Primatte” as the
current plug-in (see the buttons labeled “enable Primatte” in the screen shot
below).
During plug-in operation, you will see the composite displayed on the screen
when the “video” button is on. When the “key” button is on, you will see the
matte (alpha channel) generated by the keyer plug-in.
You can use the undo and redo buttons to the lower left of the menus to undo
and redo each step as you adjust your plug-in settings.
The Primatte menus appear to the right of the “Imagica” and “Primatte” buttons used to enable the
plugin (as described above). The left half of the Primatte menus (containing the buttons BG Image,
Ext Mask, View, Algorithm, Median Sampling, Floating Point, Auto Compute, etc) is always visible.
The right half of the Primatte menus differs depending on whether the Setup or Adjust toggle buttons
are selected. When the Setup toggle button is selected, the Key Mode Selection buttons appear in the
right half of the Primatte menus (as shown in the screen shot above). When the Adjust toggle button
is selected, the Adjust buttons appear, as shown in the screen shot below. When the Adjust Light
toggle button is selected, the Adjust Lighting buttons appear, also shown in a screen shot below.
These buttons are described further on the following pages.
3
Adjust buttons
Adjust Lighting buttons
Configuration Buttons
The buttons on the left half of the Primatte menus are generally used to configure Primatte before
starting the actual keying process. These buttons are summarized as follows. We then discuss the
actually keying process further on the following pages.
BG Image
Use this button to select a background image. Bring up the clips bin, then drag
and drop the desired background clip or image from the clips bin to the adjacent
button labeled “No Clip Selected” as shown above. Enable the “On” button next
to this to turn on the background image. Note that this button will often remain
unused in its default state, as you will often use QEffects’ layering capability to
composite the keyed foreground clip over one or more background layers. To
rephrase, if you use the “BG Image” button, the Primatte plug-in composites the
current foreground layer over a single “BG Image” or clip. Otherwise, Quantel
composites the Primatte plug-in’s result (with key channel) over the other Quantel
“background” layers. More explanation below when we discuss the “View” button.
BG Image button with “ALEX BG” clip assigned and turned “On”
Ext Mask
Use this button to select a garbage matte (external mask). Bring up the clips bin,
then drag and drop the desired external mask clip or image from the clips bin to
the adjacent button labeled “No Clip Selected” as shown above. Enable the “On”
button next to this to turn on the external mask. When enabled, white pixels in the
external mask remove (cut out) pixels from the foreground image, whereas black
pixels in the external mask leave the foreground intact (and gray pixels attenuate
the foreground based on their brightness).
Ext Mask button with “blonde matte” clip assigned and turned “On”
View
4
This button controls what Primatte displays as its render result, including the
following options: Keyed FG, Composite, Matte, Proc FG, FG, BG, Ext Matte,
Defocus Source, Status, Adj Light FG, Adj Light BG, and Hybrid Matte. The
default is Keyed FG, which you will normally use when you have multiple Quantel
layers and you’re compositing a Primatte-keyed foreground layer over them. The
other options can be useful for preview when adjusting the key, and to help see
what Primatte is doing as it operates:
5
Keyed FG
Displays Primatte’s final result, as a processed foreground
image with spill suppression in the RGB channels (displayed
when the “video” button is on), and a Primatte-generated key in
the alpha channel (displayed when the “key” button is on). Use
when you’re compositing Primatte’s result over other Quantel
layers.
Composite
Use only when you’ve assigned a background clip or image
using the “BG Image” button as described above. Displays the
foreground image composited over the assigned background,
as rendered by Primatte.
Matte
The key channel generated by Primatte. This is identical to the
alpha channel when using the “Keyed FG” view. Use this view
when picking colors and refining your result, for example when
using the “Clean BG Noise” and “Clean FG Noise” tools as
described later in this document.
6
Proc FG
Displays the processed foreground as generated by Primatte,
with spill suppression applied. This is identical to the RGB
channels when using the “Keyed FG” view. This view shows
the foreground against a black background usually with a lot of
false coloring or noisy pixels around it. The noisy pixels are
generated to maintain the fine hair or thin foreground detail,
and have spill suppression applied, which cancels out blue or
green spill that might appear around the edges of the keyed
foreground. Because the matte (key) values around the noisy
pixels will be very small and will be multiplied against the
noise, the end result will be highly desirable (the noise values
will be very transparent and will composite well against the
background).
FG
Displays the original foreground image (which can be useful for
reference when previewing).
BG
Displays the original background image assigned using the
“BG Image” button (as discussed earlier, this button will often
be unused when doing multi-layer composites in Quantel).
Ext Matte
Displays the external matte image assigned using the “Ext
Matte” button as described earlier (this can be useful for
reference during previewing).
Defocus Source Displays the foreground with Grain Removal applied (Grain
Removal is discussed later in this document). This can be
useful for reference during previewing.
Status
Displays a color coded image showing how the keyed
foreground has changed from the original foreground. This
may be helpful for troubleshooting difficult keys. Each pixel in
this view is color coded as follows:
Black = keyed FG is100% transparent.
White = keyed FG is 100% opaque w/ RGB same as original.
Yellow = keyed FG 100% opaque, RGB different from original.
Blue = semi-transparent areas of keyed FG.
Adj Light FG
Displays the foreground, with Adjust Lighting applied to areas
of backing color (for example, areas of blue screen).
Adj Light BG
Displays the extrapolated backing screen generated by Adjust
Lighting processing. This is then applied to the original
foreground to generate the Adj Light FG in the previous view.
Hybrid Matte
Displays the shrunken matte used for Hybrid Rendering (this is
applied to the foreground areas with original colors).
This concludes discussion of the View button.
7
Algorithm
The Primatte Software Plug-in offers two alternate, faster algorithms – Primatte
RT and Primatte RT+ - that you can choose for faster rendering results at the
expense of precision. The algorithm choices are further described below, with
“Primatte” being the default with highest precision:
Primatte
The default Primatte algorithm delivers the best results and
supports both the Solid Color and the Complement Color spill
suppression methods. It is the algorithm that uses three multifaceted polyhedrons (as described further down in this
document) to separate the 3D RGB color space. It is also the
default algorithm mode and, because it is computationally
intensive, it may take the longest to render.
Primatte RT
Primatte RT is the simplest algorithm and therefore, the fastest.
It uses only a single planar surface to separate the 3D RGB color
space and, as a result, does not have the ability to separate out
the foreground from the backing screen as carefully as the above
Primatte algorithm. Other disadvantages of the Primatte RT
algorithm is that it does not work well with less saturated backing
screen colors, and it does not support the Complement Color
spill suppression method.
Primatte RT+
Primatte RT+ is in between the above two options. It uses a six
planar surface color separation algorithm and will deliver results
in between the other two in both quality and performance. Other
disadvantages of the Primatte RT+ algorithm is that it does not
work well with less saturated backing screen colors, and it does
not support the Complement Color spill suppression method.
This concludes discussion of the Algorithm button.
Reset
8
Press this button to reset all Primatte parameters to their default state, and to
restore the current (target) layer to its original un-keyed foreground contents (with
blue or green screen visible).
Median Sampling
The Median picking feature is useful to filter out noisy pixels when doing sampling
and picking operations. For example, if you have a noisy image and pick a region
to sample, normally all the pixels in that region are used for the processing. To
improve upon this, you can optionally ask Primatte to apply a 3x3 median filter on
the sampled input pixels prior to performing the sampling operation. Turn on the
“Median Sampling” box to enable this.
Floating Point
By default, the Primatte library does all internal calculations in integer mode using
16-bits per RGB component. Turn on the “Floating Point” box to do all internal
calculations in floating point resolution. Floating point precision can produce
higher quality images and is faster.
Auto Compute
This is a shortcut feature which for many keying jobs, allows you to skip the first
several steps in defining your key (in other words, skip the Smart Select BG,
Select BG Color, Clean BG Noise, and Clean FG Noise steps, all of which are
described below). Auto Compute is described in more detail in a later section of
this document. Note also that Auto Compute has been improved for Primatte V5.
9
Hybrid Rendering
On the “Adj Light” page, to the far right, is the Hybrid Render button. Turn this button on to enable
Hybrid Rendering, as described below (first press the “Adj Light” button to reveal this page of
controls):
If you encounter areas where a color in the foreground object is very close to the backing screen
color, you may experience a common problem inherent in blue/green screen matting.
When you want to have a nice smooth edge as in this sample, you need to compromise and, as a
result, end up with a bluish shirt that is bleached and semi-transparent. If you try to maintain the
original blue of the cloth, then you will get rough and bluish edge on other areas of the foreground
object. Even though the shirt color is slightly different from the backing color, the edge of the FG
object frequently includes almost same color because the edge pixels are a mixture of the backing
color and the foreground object. This is why this problem often occurs.
The new Hybrid Rendering mode internally prepares both settings and combines the better portion
from each result.
In the “View” button, discussed previously, there is a new mode to view the matte used in Hybrid
Rendering. Refer to that section for further details.
In addition, below the Hybrid Render button, there are two sliders where you can adjust the matte
used for hybrid rendering. The Blur slider adjusts the blur applied to the hybrid matte, while the Erode
slider adjusts the amount the hybrid matte is shrunk. Refer to the section on the Adjust Lighting
buttons for further details.
The screen shots below show an example with original (left), result (center), and result with Hybrid
Rendering (right):
10
Key Mode Selection
When the Setup toggle button is on, the Key Mode Selection buttons appear
in the right half of the Primatte menu. The basic functionality of the Primatte
keyer plug-in is based around these ‘mode selection’ boxes (Smart Select
BG, Select BG Color, Clean BG Noise, Clean FG Noise, Spill +/-, Matte +/-,
Detail +/-, Matte Sponge, Spill Sponge, Make FG Transparent, Restore Detail
and Fine Tuning), and the image area of the desktop. Only one of the mode
selection boxes can be on at once, and this determines how the plug-in
operates when the user selects colors on the image.
These different modes represent the different steps to be taken to produce a
high quality composite image.
The first step required to produce a key using Primatte is Smart Select BG.
This button comes up highlighted as the default selection when the Primatte
plug-in is first opened.
11
Smart Select BG
Turn on the Smart Select BG box, then pick the key (background) color from
the image area using the pen (you will see a red box outlining the area you’re
picking as you drag, as shown in the screen shot below). When you release,
you should see the composite, with keyed foreground based on the colors
you’ve picked. Be sure that the “video” button (below the timeline and to the
right) is selected so you can see the composite, and that you have the proper
“View” selected (as discussed previously).
When picking colors, position the cursor in the
key color of the image area near the foreground
objects and sample the targeted background
color. Hold down the pen and drag it within the
image area to select and average the key color,
or make a single pixel selection to sample a
single color. When pen pressure is released, the
compositing process will start. If the foreground
shot was made under ideal lighting conditions,
then 90-95% of the composite will be
accomplished in this one step.
TIP: If you dragged the cursor on the key color (for example, blue screen) area, Primatte
averages the multi-pixel sample to get a single color to adjust to. Sometimes Primatte works
best when only a single pixel is sampled instead of a range of pixels. The color selected at
this point in the procedure is critical to the operation of the plug-in from this point forward.
Should you encounter problems later in the process after having selected a range of key color
shades, try Smart Select BG again with a single dark key color pixel or single light key color
pixel.
TIP: If the foreground image has a shadow in it that you want to keep in the composite, do not
select any of the darker pixels in the shadow, and the shadow will come along with the rest of
the keyed foreground image.
Select BG Color
Primatte V5 introduced the Smart Select BG button. There is still a Select BG Color button.
Although Smart Select BG is preferred, the Select BG Color button may still be useful in some
cases. The following explains the differences:
Select BG Color: Uses the traditional Primatte method of taking the sampled backing screen
color, projecting a line in the opposite direction on the hue wheel and generating artificial pixels
that MAY represent the FG object. Then, using the artificially generated foreground pixels,
internally does the Clean FG Noise operation and creates the shape of the middle and outer
polyhedrons. It then renders the composite using the generated polyhedrons.
Smart Select BG: Gets the sampled backing screen color and then analyzes the original
foreground image and determines the foreground areas using the new Primatte V5 foreground
detection routine. Then, internally, using the newly determined foreground areas, performs the
Clean FG Noise operation and determines a more desirable shape for the middle and outer
polyhedrons. It then renders the composite using the generated polyhedrons.
NOTE: The Smart Select BG operational mode is optimized for blue or green backing screens.
Primatte will work equally well with any color backing screen. It does not have to be a specific
shade of green or blue. If you are using a different color, please use the Select BG Color
operational mode to start the operation.
12
Cleaning Foreground & Background
The second and third steps in using the Primatte plug-in require the Key
(matte) to be displayed in the image area. Switch the View button to Matte,
as discussed above, to display the key signal generated by Primatte.
Note that the second and third steps should not be necessary when using
the Smart Select BG operational mode described above. These steps are
included here in case the Smart Select BG operation did not give the
desired results, or in case the older Select BG Color mode was used.
Press the Clean BG Noise box. If View is set to Matte, the image area will
display the current key. If there are any white regions in the dark “blue
screen” area, it is noise and should be removed. Move the cursor into these
areas and sample these 'white noise' regions. When pen pressure is
released, Primatte will process the data and eliminate the noise. Repeat this
procedure as often as necessary to clear the noise from the background
areas. Sometimes increasing the brightness of your monitor or changing the
screen gamma allows you to see noise that would otherwise be invisible.
Before Background noise removal
After Background noise removal
TIP: When clearing noise from around loose flying hair or any
background/foreground transitional area, be careful not to select any of
areas near the edge of the hair. Leave a little noise around the hair, as this
can be cleaned up later using the Fine Tuning tool.
TIP: Most pixels displayed as a dark color close to black in a key image will
become transparent and virtually allow the background to be the final output
in that area. Consequently, there is no need to eliminate all subtle noise in
the “blue screen” portions of the image. In particular, if an attempt is made to
meticulously remove noise around the foreground object, a smooth
composite image is often difficult to generate.
13
If there are darker or gray regions in the middle of the mostly white
foreground object, that is, if the key is not 100% in some portion of the
targeted foreground, select the Clean FG Noise mode. Use the same
techniques as with the Clean BG Noise mode, but this time, sample the
darker pixels in the foreground area until that area is as white as possible.
Again, stay away from the edges of the foreground object.
Before Foreground Noise Removal
14
After Foreground Noise Removal
Removing Color Spill
The previous steps are necessary to create a clean 'matte' or 'key'. With this key, the foreground can be composited onto any background image.
However, if there is 'spill' on the foreground object from light that was
reflected off the original background, a final operation is necessary to
remove that background spill to get a more natural looking composite.
Before Spill Removal
After Spill Removal
After the first three steps mentioned on earlier pages, there may still be
some blue fringing on areas around the hair or a blue tinge to the face or
clothing caused by light reflecting from the physical chroma key
background.
There are two ways to remove the spill color in Primatte. The simple
method is to select the Spill Sponge mode (ensure the “video” button is on,
and the View button is set properly as described earlier, so you can see the
composite) and then sample the spill areas away. By just positioning the
cursor over a bluish pixel on the foreground object and selecting it, the blue
will disappear and be replaced by a more natural color. You can also drag
on the screen to select a region of pixels containing spill.
Note: This operation works on foreground 'color regions'. In the image
above, samples should be made on the hair fringes, and also on the inside
of the left arm below the sleeve.
Spill Process functions:
When the Adjust toggle button is on, a group of “Adjust buttons” appear on the
right half of the Primatte menu. Included in these is the Spill Process list box,
which controls which colors replace the foreground areas with spill.
When Complement is on, Primatte replaces color spill with the background
color's complementary color. For a spill (key) color of blue, this is usually a
yellowish color. Complement is the default setting, as shown below.
15
The Solid Replace function replaces color spill with a solid color, selected
in the Palette menu (shown below). The replacement color in this mode is
by default gray (R128, G128, B128). When Solid Replace mode is
selected, the Palette menu is displayed to the right of the Spill Process
buttons, allowing the user to select a color other than gray.
Note: If the foreground object was a person wearing a red shirt and the user
was having difficulty removing the blue spill from the shirt, he could use this
feature and select a color close to the red shirt color to replace the spill. This
sometimes results in a better edge around the foreground object.
The Palette menu allows the selection of and displays the current Solid
Replace color (by default, it is gray; R128, G128, B128). By clicking on an
area of the color wheel, the user is selecting a color (other than the
complement) to be used in replacing color spill.
A number of color pots appear to the left of the color wheel. These allow you
to select preset colors, including several shades of gray. Selecting any of
these shades of gray positions the color selector cursor at the center of the
color wheel. The gray scale value can then be controlled from the gray scale
bar (to the right of the color wheel).
16
Defocus Replacement mode
The Defocus Replacement mode uses a defocused copy of the background image to determine
the spill replacement colors instead of a solid palette color or just the complement color. This mode
can result in good color tone on the foreground object even with a high contrast background. As in
the example below, spill can even be removed from frosted glass using this feature and still retain
the translucency.
On the negative side, the Defocus Replacement mode sometimes results in the fine edge detail of
the foreground objects getting lost. Another problem could occur if the user wanted to later change
the size of the foreground image against the background. Since the background/foreground
alignment would change, the applied color tone from the defocused image might not match the new
alignment.
Blue Suppression of a Frosted Glass Object
17
Fine Tuning the Composite
If the spilled color was not totally removed using the above procedure, a finetuning operation should follow for more subtle and sophisticated removal of
the spilled background color.
Select the Fine Tuning mode, then using the cursor, sample a small range
of the pixels exhibiting color spill that you want to remove. When you lift the
pen, three fine tuning number boxes will appear: LPoly-spill, MPoly-matte,
and SPoly-detail. At this time, Primatte will display the selected color in a
color swatch box (just to the right of the number boxes).
For most images, the LPoly-spill function (which affects the Large
Polyhedron, further details in the last section below) is all that is required to
remove any remaining color spill. Cursor movement on the LPoly-spill control
performs a color adjustment of the sampled color against the background.
The more to the right the cursor moves (while dragging), the less of the key
color component (or spill) will be included. The more to the left the cursor
moves, the closer the color component of the selected region will be to the
original foreground image. If moving the control all the way to the right does
not achieve the desired result, re-sample the color on the monitor image and
again move the LPoly-spill control to the right. These operations are additive
and can be repeated as necessary to get the desired results.
Note that when using the LPoly-spill control in Fine Tuning mode to
remove spill, spill colors will be replaced based on the setting of the Spill
Process list box (to Complement, Solid Replace, or Defocus).
TIP: It is better to make several small adjustments to the spill areas than a
single large one.
The two other Fine Tuning number boxes can be used in the same way
for different key adjustments.
The SPoly-detail function controls the matte softness for the color that is
closest to the background color. For example, you can recover lost rarefied
smoke in the foreground by selecting the Fine Tuning operational mode,
clicking on the area of the image where the smoke just starts to disappear
and moving the SPoly-detail control to the left.
18
Note that the SPoly-detail control shrinks the small polyhedron and releases
pixels that were close to the background color (the small polyhedron
contains all the blue or green background colors and is described further in
the last section below). The SPoly-detail Control is useful for restoring
foreground image pixels that were lost in the original sample because they
were so similar to the background color.
The MPoly-matte function controls the matte softness for the color that is
closest to the foreground color. For example, if you have thick and opaque
smoke in the foreground, you can make it semi-transparent by moving the
MPoly-matte control to the right after selecting the pixels in the Fine Tuning
mode.
Note that the MPoly-matte control affects the Medium Polyhedron (further
details in the last section below) and adjusts the transparency of the matte
against the sampled color. The more to the right this control is moved, the
more transparent the foreground object becomes in the selected color
region.
TIP: If the foreground image changed color dramatically during the finetuning process, you can recover the original color by re-sampling an area
of the off-color foreground image and moving the LPoly-spill control
slightly to the left. This may introduce some spill back into that color
region. Again, use the LPoly-spill control to suppress the spill, but make
smaller adjustments this time.
If these final 'spill suppression' operations have changed the final
compositing results, you may have to return to earlier operations to clean up
the matte. If the Composite view looks good, but a 100% foreground area
has become slightly transparent, you can clean those transparent areas up
by using the Matte Sponge function. After selecting Matte Sponge, just click
on the transparent pixels (gray on the white foreground object when viewing
the key), and they will become 100% foreground (or white). All of the spillsuppression information will remain intact during this operation.
Alternatively, using the matte view, select Fine Tuning mode, then select
those transparent areas in the image and move the MPoly-matte control
slightly to the left. This will move that color region from 0-99% foreground
with spill suppression to 100% foreground with spill suppression and should
solve the problem.
Make Foreground Transparent
When this mode is selected, the opaque foreground color region sampled
in the image window becomes slightly translucent. This operation is useful
for making foreground objects that are otherwise 100 percent covered with
smoke or clouds visible. To use this mode, select the “Make FG
Transparent” box then drag on the image and release to select the desired
color region of interest in the foreground that you want to make
transparent.
19
Restore Detail
With this mode selected, the completely transparent background region
sampled in the image window becomes translucent. This operation is useful
for restoring lost hair details, thin wisps of smoke and the like. It shrinks the
small polyhedron slightly. To use this mode, select the “Restore Detail” box,
then drag on the image and release to select the color region of interest that
you want to make translucent.
Spill Sampling Tools (Spill + and Spill -)
Using the Spill(+) and Spill(-) modes, you can gradually remove or recover
the spill intensity on the foreground object by sampling the referenced color
region repeatedly. The conventional Spill Sponge tool removes the spill
component in a single action at one level and does not allow sampling the
same pixel a second time. Even though just a small amount of spill needed
to be removed, the Spill Sponge removed a preset amount without allowing
any finer adjustment.
Effect of Spill(+/-) Repeatable Sampling
Matte Sampling Tools
The Matte(+) and Matte(-) modes are used to thicken or attenuate the
matte information. If you want a thinner shadow on a foreground object, you
can use the Matte(-) mode as many times as you like to make it more
transparent. On the other hand, you can use the Matte(+) mode to make the
matte thicker in that color region.
Effect of Matte(+/-) Repeatable Sampling
Detail Sampling Tools
The Detail(+) and Detail(-) modes are a refined version of Clean BG Noise
and Restore Detail. For example, when you see some dilute noise in the
backing area but don't want to remove it completely because it affects some
fine detail in a different area, try using Detail(-). It will attenuate the noise
gradually as multiple samples are made on the pixel. You should stop the
sampling when important fine details start to disappear.
Effect of Detail (+/-) Repeatable Sampling
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Adjust Buttons When the Adjust toggle button is selected, several Adjust buttons appear in the right half of the
Primatte menu. These include the Spill Process list box (discussed previously), along with the Grain,
Shrink, and Defocus controls. This section discusses the latter controls.
Defocus
This tool is used to soften a hard-edge that might sometime occur after keying out
the background. Moving this number box in a positive direction determines the
defocusing level being applied to the matte (key). The direction of the blur can be
modified using the Inward Defocus button (see next tool description).
Inward Defocus A method of defocusing the matte where the softening is only applied inwardly,
toward the center of the foreground subject. The default Primatte defocus feature
affects the matte edges in both directions (inward and outward) and sometimes
introduces a halo artifact around the foreground object's edge in the composite
view. This can be most evident when using the Complement Spill Process mode.
With the Inward Defocus button turned on, the matte defocus functions only in the
inward direction of the foreground subject (toward the center of the white area). The
21
final result is that it removes small and dark noise in the backing area without
picking them up again in the Clean BG Noise mode and sometimes results in
softer, cleaner edges on the foreground objects and no halo effect around the
foreground object.
Shrink Determines the degree of background penetration into the foreground around the
silhouette of the foreground object. The effect is likened to ’shrinking’ the matte
(key). Note: With using this feature, foreground details like wisps of hair and
smoothness of motion blur may be adversely affected. Set it to 0 for optimum
results with such details.
Grain Type The Grain Tools are used when a foreground image is highly compromised by film
grain. As a result of such grain, when backing screen noise is completely removed,
the edges of the foreground object often become harsh and jagged leading to a
poor key. These tools were created to, hopefully, help when a compositing artist is
faced with a grainy image.
These tools default to off, when the Grain Type list box is set to No Grain. To
enable grain removal, set the Grain Type list box to one of the following values:
Small Grain
When Small Grain is selected, the user gets the average color of a
small region of the area around the sampled pixel. This should be
used when the grain is very dense.
Medium Grain When Medium Grain is selected, the user gets the average color of
a medium-sized region of the area around the sampled pixel. This
should be used when the grain is less dense.
Large Grain
When Large Grain is selected, the user gets the average color of a
larger region of the area around the sampled pixel. This should be
used when the grain is very loose.
When you enable grain removal, a Grain Tolerance number box appears below the
Grain Type list box.
The larger the grain size the larger the resulting reduction in grain. However, if the
grain size is too large then it may result in loss of edge and foreground areas. The
grain tolerance is very sensitive and so you should try to use small values
otherwise it can cause weird results:
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23
As said, the Grain Tools handle cases when there is a lot of noise in the foreground
image that makes producing a good extraction difficult. For example, consider the
following case:
Doing too much ‘clean background’ (Clean BG Noise) sampling to reduce the noise
in the background will adversely affect the edges and loose detail:
In this case, the Grain Tools can used to clean the background but still preserve the
fine edges as follows. Just set the Grain Type and Grain Tolerance controls as
described above, then use the Clean BG Noise tool to remove gray areas from the
background.
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Adjust Lighting Buttons When the Adjust Light toggle button is selected, controls for Adjust Lighting appear to the right, as
shown below.
Adjust Lighting is an optional feature that automatically will improve the lighting of the foreground to
account for poor actual lighting. For example, you can have images which have many different hues
of blue because the lighting was not well controlled. Essentially a new “adjusted light” foreground is
generated which will be used in further Primatte processing. This will make the traditional Primatte
keying algorithm produce superior results. The implementation uses a patent pending algorithm that
generates a grid to analyze which parts of the image are considered true blue/green screen or
foreground or a simulated blue/green color will be generated.
The Adjust Lighting algorithm uses a set of samples in the image that it establishes on a regular grid
pattern. The algorithm will determine if they are classified as a pure blue/green background sample,
or a simulated background sample or a foreground sample. The simulated case is generated based
on the neighborhood grid samples.
To enable Adjust Lighting, simply turn on the Adjust Lighting button, to the bottom left as shown in the
screen shot above.
To the right, below the blue Adjust Lighting label, appear the following three other controls. The
default settings for these will often be fine, but the controls are there in case you need to make
precise changes:
Outer Boundary
Often you can find noisy or black pixels on the boundary. To avoid these from
polluting the results of the adjust lighting operation, you can set a boundary that
will be ignored for the processing. The default is 5.
Grid Size
Increase this value if you would like more precision in the Adjust Lighting
process. The default is 12.
Threshold
The threshold used in the Adjust Lighting algorithm to determine if a grid pixel
should be treated as a pure blue/green background sample, or a simulated
background sample or a foreground sample. The default is 10.
In the “View” button, discussed previously, there are two new modes to view the intermediate results
used by Adjust Lighting. Refer to that section for further details.
Also grouped with the Adjust Lighting buttons, to the far right, is a button to enable or disable Hybrid
Render. Below this, there are two sliders where you can adjust the matte used for hybrid rendering.
The Blur slider adjusts the blur applied to the hybrid matte, while the Erode slider adjusts the amount
the hybrid matte is shrunk. Refer to the previous section on Hybrid Rendering for further details.
The images on the following page show an example of how Adjust Lighting improves your chromakey results.
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Original Foreground
Keyed Image
Keyed Image with Adjust Light enabled
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Auto Compute
Using the Auto Compute button may make your keying operation much easier. You can click on this
button as a first step and it may automatically sense the backing screen color, eliminate it and even
get rid of some of the foreground and background noise that would normally be cleaned up in Steps 2
(Clean BG Noise) and 3 (Clean FG Noise) of the Primatte operation. If you get good results with
Auto Compute, you can proceed immediately with spill removal (using Spill Sponge, Spill +/-, etc).
When you turn on the Auto Compute button, two related number boxes appear. You can use these
two controls to fine tune the results of Auto Compute (the composite will update each time you adjust
either slider):
FG
This number box controls cleanup of noise in the foreground. Positive values have a stronger
effect on FG noise, while negative values have a milder effect on FG noise.
BG
This number box controls cleanup of noise in the background. Positive values have a stronger
effect on BG noise, while negative values have a milder effect on BG noise.
For Primatte V5, Auto Compute has been improved to better handle cases where the background
area is small, and cases where the foreground contains similar colors to the background.
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Rendering the Whole Clip
When the desired composite has been achieved, the whole clip needs to
be processed before it can be used elsewhere. Select the Render box to
start the rendering process. When complete, the resulting composite will
be available in the library. See the “Using QEffects” chapter in the
QEffects Application Reference for further details on rendering.
More about the Primatte Polyhedral Slicing Algorithms
There are three Primatte algorithms: Primatte, Primatte RT+, and Primatte RT.
Here is a chart that shows the main differences between them:
These algorithms are discussed in detail in the following sections.
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The Primatte Algorithm
Explanation of how Primatte works
The Primatte chroma key algorithm is a sophisticated method of color space
segmentation that can be easily explained to help a user achieve maximum
effectiveness with the tool. Basically, Primatte segments all the colors in the
foreground image into one of four separate categories. The result is a 'spill
suppressed' foreground image and a matte which is used to apply the
modified foreground to a suitable background. Primatte works in 3D RGB
color space. Here is a visual representation of the Primatte algorithm after
an image has been processed.
By operating the Primatte interface, the user essentially creates three
concentric, multi-faceted polyhedrons. These can be pictured as three
globes (polyhedrons or polys), one within the other, which share a common
center point. The creation of these polyhedrons separates all possible
foreground colors into one of four regions; inside the small polyhedron (1),
between the small and medium polyhedrons (2), between the medium and
the large polyhedrons (3) and outside the large polyhedron (4).
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The four regions created are described as follows:
Region 1 (inside the small polyhedron) - This region contains all of the foreground image colors that
are considered 100% background. These are the green or blue or whatever colors that were used as
the backing (key) color of the foreground image.
Region 2 (between the small and medium polyhedrons) - This region contains all the foreground
colors that are at the edges of the foreground object(s), in glass, glass reflections, shadows, sheets of
water and other transparent and semi-transparent color regions. These color regions also have spill
suppression applied to them to remove color spill from the backing screen.
Region 3 (between the medium and large polyhedrons) - This region contains all the foreground
image colors that are 100% foreground but have spill suppression applied to them to remove color
spill from the backing screen. Otherwise they are 100% solid foreground colors.
Region 4 (outside the large polyhedron) - This region contains all the 100% foreground image colors
that are not modified from the original foreground image. There is no spill suppression applied to
these colors.
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In the first step in using Primatte (Select BG Color), the user is asked to indicate the backing (key)
color on the original foreground image. The sample should usually be taken from a 'medium shaded'
area near the foreground object. By 'medium shaded' area, it is meant that if green is the backing
color and the green area of the foreground image has many shades of green ranging from very pale
green to almost black, a shade of green in-between these extreme ranges should be chosen. If good
results are not obtained using this sample, Primatte should be reset and another sample taken using
a slightly darker or lighter shade of green. The first sample of Primatte often determines the final
result as the center point of all three polyhedrons is created based on this first sample.
A single pixel may be selected or a range of pixels (rectangular sample). If a range of pixels is taken,
the sample will be averaged to get a single color sample. This single pixel or averaged color sample
then becomes the center of the small polyhedron. A few other shades around that color are included
in the original small polyhedron.
NOTE: It is recommended that a single pixel be selected as the first sample as you then have some
idea where the center point of the polyhedrons is located. If a rectangular sample is made, you can
only guess at the average color that ends up being the center point. You can get an idea how this
sample affects the algorithm by resetting the Primatte plug-in, going to the Matte View and clicking
around on the green or blue screen area while in the Select BG Color operation mode. You can
immediately see the results of the initial settings of the polyhedrons in this way.
After making a sample of the backing screen (key) color in the first step, the result is a small golf ballshaped poly as shown in the following image.
The second step in using Primatte is to clean up the backing color area by adding additional shades
of green or blue to the small poly. This second step (Clean BG Noise) is usually executed while
viewing the black and white Matte View.
Before BG Noise Removal
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After BG Noise Removal
While in the Clean BG Noise sampling mode, the user samples the white milky regions as shown in
the left-hand image above. As the user samples these regions, they turn to black as shown in the
right-hand image above.
What is happening in the Primatte algorithm is that these new shades of green or blue (the white
milky areas in the matte view) are added to the small poly. The left hand image below shows the new
pixels sampled (white dots) in relation to the small poly, and the image next to it shows how the small
poly extends outward to encompass the newly sampled colors into the small poly.
The advantage of this technique is that the polyhedron distorts to enclose only the shades of blue or
green that are in the backing screen. Other shades of blue or green around these colors are left
undisturbed in the foreground. Other chroma keyers expand from a golf ball-sized shape to a baseball
to a basketball to a beach ball. Since it expands in all directions, many shades of color are relegated
to 100% background making it hard to get good edges around the foreground objects.
Now that the user has created a small polyhedron, they must shape the medium and large polys. A
default medium and large poly are both automatically created and are then modified based on the
next couple of Primatte operations. The third Primatte step (Clean FG Noise) is to sample and
eliminate gray areas in the 100% foreground area of the image.
After FG Noise Removal Before FG Noise Removal
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Again, the user makes several samples on the dark, grayish areas on the foreground object until it is
solid white in color. Primatte is shaping the large polyhedron with each color region that is sampled.
Care should be taken in both this and the previous steps to not sample too close to the edges of the
foreground object. Getting too close to the foreground object's edges will result in hard edges around
the foreground object. Primatte uses these samples to modify and shape the polys to the desired
shape. At this point, the matte or key has been created and would allow the foreground objects to be
composited into a new background image.
If the user changes the display mode from black and white Matte View to color Keyed FG View (or
Composite View if a BG Image is used), there is usually 'color spill' on the edges (and sometimes the
center) of the foreground objects. When on the edges of the foreground object, this spill comes from
where the edges of the foreground object blended into the backing color. If it is on the center of the
foreground object, it usually results from reflected color from the backing screen. The next Primatte
step, either Spill Sponge, Fine Tuning or Spill(-), can now be used to eliminate this spill color.
Let's take a look at what is happening in the Primatte algorithm while this next step is performed. Here
is what the various tools in Primatte do to the Polyhedrons when they are used:
As you can see above, the Spill Sponge bulges the large polyhedron in the color region specified. A
color region is specified by clicking on the image in a particular area with spill present. For example, if
the user clicks on some spill on the cheek of a foreground person, Primatte goes to the section of the
large polyhedron closest to that particular flesh tone and bulges the polyhedron there. As a result, the
flesh tones move from outside the large poly to in-between the medium and large polys. This is
Region 3 and, if you remember, is 100% foreground with spill suppression. As a result of the
suppression, the spill is removed from that cheek color and all other shades of that color on the
foreground. The user would then continue to sample areas of the image where spill exists and each
sample would remove spill from another color region.
When all spill has been removed, the user should have a final composite. As a last step, the user
should go back to the Matte View and make sure that gray, transparent areas have not appeared in
the foreground area. If there are any, the Matte Sponge operation mode should be selected and
those gray pixels should be sampled until they have all turned white again.
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The Matte Sponge and Spill Sponge tools bulge or dent the polyhedrons a pre-selected amount. If
the desired results are not achieved or the results are too extreme for the image, a manual method
can be applied. The user should then choose Fine Tuning mode, select a color region of interest and
then move the appropriate slider (number box) to get the desired results.
For example, to remove spill, select a region of the composite image with spill on it. Move the LPolyspill (large poly) slider to the right a little bit - the large poly will bulge and the spill should disappear.
Move it a little more, if necessary. Moving this slider to the right removes spill (moves the colors from
outside the large poly to between the medium and large polyhedrons), and moving it to the left dents
the large poly and moves that color region to outside the large poly.
If the user samples a foreground object shadow and then moves the MPoly-matte (medium poly)
slider to the right, the shadow will become more transparent. This is useful for matching composited
shadows to shadows on the plate photography. It can also be used to make clouds or smoke more
transparent.
If some foreground detail disappears during the composite, the user can select where the detail
should be and then move the SPoly-detail (small poly) slider to the left. This dents the small poly in
that color region and releases the detail pixels from the small poly into the visible region between the
small and medium polyhedrons.
The Spill Sponge and Matte Sponge tools are 'shortcut tools' that automatically move the sliders a
pre-selected amount as a timesaving step for the user. Other 'shortcut tools' include the Make FG
Transparent tool and the Restore Detail tool.
These 'shortcut tools' are one-step operations where the user clicks on a color region of interest and
Primatte performs a pre-calculated operation. Hopefully, most operations using Primatte would only
require these tools, but the manual operation of the Fine Tuning sliders is always an option.
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The Spill(-) tool bulges the large poly a small amount incrementally in the color region that is clicked
on and the Spill(+) tool dents it a small amount with each click. The Matte(-) and Matte(+) tools do
the same to the medium poly and the Detail(-) and Detail(+) do it to the small poly.
Explanation of how Primatte RT+ works
The Primatte RT+ algorithm differs from the Primatte algorithm in that it has a six surface color
separator instead of the 127-faceted polyhedrons. This makes the Primatte RT+ algorithm much
simpler and, therefore, faster to calculate. The results and performance of Primatte RT+ falls in
between the Primatte and Primatte RT options. Where the Primatte RT+ algorithm might not work
well is with less saturated backing screen colors, and it also does not support the Complement Color
spill suppression method (which is the spill suppression method that delivers the best detail). For a
well-lit and photographed image or clip, this algorithm will produce good results and render quickly.
Here is what a visual representation of the Primatte RT algorithm looks like after an image has been
processed:
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Explanation of how Primatte RT works
Primatte RT is the simplest algorithm and, therefore, the fastest. It uses only a single planar surface
to separate the 3D RGB color space and, as a result, does not have the ability to separate out the
foreground from the backing screen as carefully as the above Primatte algorithm. Like the Primatte
RT+ algorithm, Primatte RT might not work well with less saturated backing screen colors and it too
does not support the Complement Color spill suppression method (which is the spill suppression
method that delivers the best detail). For a well-lit and photographed image or clip, this algorithm will
produce good results and render very quickly.
Here is what a visual representation of the Primatte RT algorithm looks like after an image has been
processed:
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Index
Adj Light FG view mode
Adj Light BG view mode
Adjust Lighting
Adjust Lighting toggle button
Adjust toggle button
Algorithm
Auto Compute
BG Image
BG view mode
Clean BG Noise
Clean FG Noise
Complement Replace
Composite view mode
Configuration buttons
Defocus
Defocus Replace
Defocus Source view mode
Detail +, Ext Mask
Ext Matte view mode
FG view mode
Fine Tuning
Floating Point
Grain Tolerance
Grain Tools
Grain Type
Hardware Assisted Plug-in
Hybrid Matte (view mode)
Hybrid Rendering
Inward Defocus
Key button
Keyed FG view mode
LPoly-spill
Make Foreground (FG) Transparent
Matte +, Matte Sponge
Matte view mode
Median Sampling
MPoly-matte
Palette menu
Polyhedrons
Primatte Algorithm
Primatte RT Algorithm
Primatte RT+ Algorithm
Proc FG view mode
Redo
Reset
Restore Detail
Select BG (Key) Color
Setup toggle button
Shrink
Smart Select BG
Software Plug-in
Solid Replace
Spill +, Spill Process
Spill Sponge
SPoly-detail
Undo
Video button
View
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7
7
25-26
3, 25
3, 15, 21
8, 28, 29, 35, 36
9, 27
4–6
6
5, 9, 11, 13, 14, 20, 22, 24, 27, 31, 32
5, 9, 11, 14, 27, 32
8, 15, 18, 21
5
4
21
17
7
20, 35
4
6
6
18, 19, 33, 34
9
22-24
22-24
22-24
2
7
10
21
3
5
18, 19, 34
19, 34
20, 35
19, 33, 34
5
9
18, 19, 34
16
8, 18, 19, 20, 29-36
8, 28-34
8. 28, 36
8. 28, 35
6
3
8
20, 34
9, 11, 12, 31
3, 11
22
9, 11, 12
2
16, 18
20, 35
15, 16, 18, 21
11, 15, 20, 27, 33, 34
18, 19, 34
3
3
5-7
38