Add "CICP in images"

[svgeesus]

Coding Independent Code Points (CICP) is a colorspace labeling technology, originally deployed for video but now also used for still images or animated images. It is standardized in ITU H.273.

Compared to an ICC profile, CICP adds much less data to an image (four bytes, instead of a few 10s of kbytes) but cannot represent all color spaces (such as CMYK). It can, however, fully label the increasingly popular Display P3 colorspace and, for HDR, BT.2100-HLG and BT.2100-PQ.

CICP is already used in AVIF and JPEG XL images. PNG Third Edition also added CICP support. The current state of CICP in PNG is described in the PNG implementation report and, for browsers, can be summarized like this:

• Blink-based browsers support it in AVIF and PNG
• WebKit-based browsers on macOS (14+), iOS and iPadOS rely on the native platform support for CICP
• Gecko-based browsers support it in AVIF, and plan to support it in PNG also

Related:

• Narrow range and cICP w3c/png#312
• 32-bit HDR PNG #6987
• Add "HDR AVIF" image support #6504
• Add tracking for "Ultra HDR JPG" #6759

[svgeesus]

As an update, the PNG implementation report shows CICP in PNG passing in Chrome 137, Edge 137, Firefox 141, Safari TP 127 and Ladybird 1. Servo does not yet have support.

I also wrote a deep dive explaining CICP