5 ms·
ISO/TS 22028-5:2023 Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 5: High dynami
by altairprime 3y ago
ISO/TS 22028-5:2023
Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 5: High dynamic range and wide colour gamut encoding for still images (HDR/WCG)
https://www.iso.org/standard/81863.html https://www.iso.org/standard/81863.html
Note that, in this specification’s title, “HDR” refers to luminosity ranges that are broader than sRGB supports, and “WCG” refers to colorspaces that are broader than sRGB supports.
Apple’s video is focused on the HDR component of still images, which is relatively new and not yet finalized into any ISO or W3C standards.
Support for WCG images is already widespread courtesy of ICC profiles, though many holdouts (such as Slack and Discord) continue to damage WCG images posted to their services.
Quoting Apple’s video transcript at this time index:
https://developer.apple.com/wwdc23/10181?time=205 https://developer.apple.com/wwdc23/10181?time=205
> This specification, TS22028-5, provides a structure for encoding HDR content into existing still image formats without compromising quality.
> The specification requires Hybrid Log-Gamma, HLG, or Perceptual Quantizer, PQ, as the encoding transfer function. These are functionally analogous to the gamma curves used in SDR images.
> The color primaries for ISO HDR files are the BT.2020 primaries
> HDR images are required to be 10 bits or more per component. This means that some formats, like HEIF, can encode HDR, but some others, like traditional JPEG, are not able to be 22028-5 compliant, as they only support 8 bits per component.
PNG only supports 8-bit or 16-bit, making it quite inefficient for 10- and 12-bit HDR. However, JPEG-XL seems to support 10 bits or more per component. This may provide supporting context for why Apple began supporting a new image format this fall.
> for required metadata, both traditional ICC profiles and CICP tags are valid.
- the8472 3y agoIsn't that just BT.2100?
- turnsout 3y agoYeah, it does appear to be a reiteration of Rec. 2100 / BT.2100. I wonder if it's because this refers to still images rather than video?
- altairprime 3y agoYes, that’s why: https://stage.color.org/hdr/07-Nicolas_Bonnier.pdf https://stage.color.org/hdr/07-Nicolas_Bonnier.pdf (slide “Motivations”): > Several attempts to use PQ/HLG and BT.2020 for still photography are surfacing > But so far, the digital still imaging industry has not settled on a reference HDR/WCG image encoding for consumers > The purpose of TS 22028-5 is to provide requirements and guidelines for HDR/WCG colour encoding of still images And a bit further down, referring specifically to BT.2100: > Shall use ITU-R BT.2020/2100-2 colour primaries
- pornel 3y agoBTW, the old JPEG is a ~12-bit format. It's widely assumed to be an 8-bit format, because libjpeg by default gives you output truncated to 8 bits. Unfortunately, libjpeg made higher depth outputs an either-or compile-time option that breaks the ABI, so nobody enables that mode.
- altairprime 3y agoTIL, and thanks for pointing that out. Apparently there’s a tiny subset of PNG world that can cope with bit-shifted 12-bit, but apparently like JPEG, support is diminished and ultimately not dependable.