replaces each color value in the given image, by using it as an
index to lookup a replacement color value in a Color Look UP Table
in the form of an image. The values are extracted along a diagonal
of the CLUT image so either a horizontal or vertial gradient image
can be used.
Typically this is used to either re-color a gray-scale image
according to a color gradient in the CLUT image, or to perform a
freeform histogram (level) adjustment according to the (typically
gray-scale) gradient in the CLUT image.
When the 'channel' mask includes the matte/alpha transparency
channel but one image has no such channel it is assumed that that
image is a simple gray-scale image that will effect the alpha channel
values, either for gray-scale coloring (with transparent or
semi-transparent colors), or a histogram adjustment of existing alpha
channel values. If both images have matte channels, direct and normal
indexing is applied, which is rarely used.
replaces each color value in the given image, by using it as an index to lookup a replacement color value in a Color Look UP Table in the form of an image. The values are extracted along a diagonal of the CLUT image so either a horizontal or vertial gradient image can be used.
Typically this is used to either re-color a gray-scale image according to a color gradient in the CLUT image, or to perform a freeform histogram (level) adjustment according to the (typically gray-scale) gradient in the CLUT image.
When the 'channel' mask includes the matte/alpha transparency channel but one image has no such channel it is assumed that that image is a simple gray-scale image that will effect the alpha channel values, either for gray-scale coloring (with transparent or semi-transparent colors), or a histogram adjustment of existing alpha channel values. If both images have matte channels, direct and normal indexing is applied, which is rarely used.