Compositing

Perceptual and subtractive mixers, backgrounds, and the shared dispatcher. Concepts: Color compositing.

Modes & dispatcher

combine_colorized_layers	Combine a list of already-colorized RGB layers into a final image, applying a compositing mode / blend / gamma / inverse / background.
combine_multicolor_colorspace	Combine colorized RGB layers in a perceptual color space instead of by direct RGB channel addition.
combine_multicolor_alpha	Combine colorized layers by compositing over a chosen background.
COMBINE_MODES	Built-in immutable sequence.
COLORSPACES	Built-in immutable sequence.
BLENDS	Built-in immutable sequence.

Backgrounds & paint mix

composite_over_background	Composite a black-background (premultiplied-alpha) colorized/combined image over a solid background color, or produce a transparent RGBA image.
layer_coverage	Per-pixel coverage (HSV-style "value") of a colorized layer.
rgb_to_ryb	Vectorized sRGB -> RYB conversion (Sugita & Takahashi 2017).
ryb_to_rgb	Vectorized RYB -> sRGB conversion (Sugita & Takahashi 2017).
rgb_to_cmyk	Vectorized sRGB -> CMYK conversion (standard, no UCR/GCR).
cmyk_to_rgb	Vectorized CMYK -> sRGB conversion.

Lab / HSV / HSL helpers

rgb_to_lab	Convert an sRGB image (values in [0,1], shape (...,3)) to CIE L*a*b*.
lab_to_rgb	Convert a CIE L*a*b* image back to sRGB in [0,1].
rgb_to_hsl	Vectorized RGB to HSL conversion.
hsl_to_rgb	Vectorized HSL to RGB conversion.
mix_colors_hex	Mix solid colors (not images) in a chosen color space.
greyscale_image	Convert a finished RGB composite to greyscale, e.g. to check how it will look in a B&W print.
simulate_colorblindness	Simulate how an RGB composite appears with a color vision deficiency, to help pick layer colors that stay distinguishable for all viewers.

Swatches

combo_swatch	Render the composite-mode-aware color-combination swatch.
swatch_layout	Circle centers/radii (pixel coords of a size x size canvas) for the overlapping color-combination swatch.

Transparent cutouts

make_transparent_cutout	Build a transparent-sky RGBA cutout from an RGB (or RGBA) composite.
save_transparent_cutout	Write an RGBA cutout to PNG or TIFF (format from the file extension).
preview_cutout_on_backgrounds	Show the cutout over several backgrounds (default: checkerboard, dark, light).
batch_transparent_cutouts	Apply make_transparent_cutout() to a list of RGB images with shared settings.
deblend_background	Recover an RGBA foreground from a composite flattened onto a known solid background color (un-premultiply) — the inverse of flatten_rgba() and the principled sibling of make_transparent_cutout().
flatten_rgba	Composite an RGBA image onto a solid background color (the inverse of deblend_background()).
luminance	Rec.
alpha_from_intensity	Build a soft alpha matte from a 2D intensity map.
make_checkerboard	Soft grey checkerboard background for previewing transparency.