keyspillm0pup

This plugin removes the residual key color fringing, which can
remain after chroma key compositing.


Written by Marko Cebokli,  apr 2012,  and released under GNU GPL


RELEASE NOTES

** apr 2012
Version 0.1
"pre-alpha" (throw it out and see what happens... :-)



DESCRIPTION

After some experimentation with chroma keying, it looked to me that
there is no single method of key cleaning, that works in all
situations, like keyspill on bright, keyspill on dark, etc.
So I included several cleaning options, which can be used alone
or in combination.
In short, it offers three ways of pixel selection (masking), that
can be combined with four types of color changing operations.
The three selection / masking modes are based on
- similarity to key color
- transparency
- closeness to the edge
and the four things that can be done to the selected pixels are
- move away from the key color (De-Key)
- move towards an target color (Target)
- desaturate
- luma (brightness) adjust.


MASKS

Color difference masks are based on the color of the image, and do
not depend on the alpha from the preceding keying, except for
ignoring the 100% transparent areas, to increase speed.

Transparency and Edge masks are based on the alpha channel from the
preceding keying operation.
Transparency masks will affect only the parts that are neither 100%
opaque nor 100% transparent, based on the alpha values from the
preceding keying operation. The effect will be proportional to the
transparency.
NOTE: if a "hard key" was used in the preceding keying, there will be
no areas that T operations could affect.
Edge maskss will affect only pixels close to the edge, with the effect
diminishing away from the edge. The outer edge is the edge of the
fully opaque part, where the alpha from the preceding keying
is 1.0 (255).
NOTE: the edge masking algorithm is not yet what I would like it
to be. I will have to look some more into this, and improve it, so
consider it a "temporary solution" that will change in the future.

All masks can be further pruned with two parameters: an "hue gate",
which will limit the mask to hues close to the key hue, and an
"saturation threshold", which will limit the mask to areas with
color saturation above a threshold.


CASCADING

This plugin can be cascaded, but it is not possible to get the same
color based mask in the second instance, because the colors will be
changed by the first instance. To enable two operations with the
same mask, each plugin instance can do two opertions.
With transparency and edge masks, cascading is a bit easier.
If the hue gate and saturation threshold are not used, transparency
and edge masks can be exactly the same in cascaded plugins.


PARAMETERS:

Key color:
This should be the same or similar to the key color used for the
preceding keying operation.

Target color:
This is only used when "Target" operation is used with one of the
masks. The colors in the affected areas will be moved towards this
color, according to the "Amount" parameter.

Mask type:
Selects the type of mask that will determine where the color
altering operations will occur.

Tolerance:
For the color difference mask, the range of colors around the key,
that will be 100% affected.
For the transparency mask, the "amplification".
For the edge mask, the width of the affected area.

Slope:
For the color difference mask, the range of colors outside of
"Tolerance", that will be gradually less affected.
No function for the transparency and edge masks.

Hue gate:
Reduces the mask according to difference from key hue, to prevent
change to pixels that are within the mask, but not polluted by key.

Saturation threshold:
Reduces the mask according to color saturation, to avoid affecting
the neutral areas.

Operation 1:
Selects which of the four possible operations will be done on the
mask-selected pixels. Apart from no operation, there are four
possibilities: De-key, Target, De-saturate and Luma adjust.

Amount 1:
The amount of the selected operation 1, how much the colors will
change.

Operation 2, Amount 2:
Enable a second operation to be performed with the same mask.

Show mask:
This will show the selected mask as a greyscale image, to help with
fine tuning of the masks. Shoud be OFF for the final render.

Mask to Alpha:
Copies the active mask to the alpha channel.
For all normal spill cleaning operations, this should be OFF.
By seting it ON, the keyspillm0pup itself can be used as a keyer,
or to generate some special effects.