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Lossless WebP is very good indeed. The main problem is that it is not very future-proof since it only supports 8-bit. For SDR images that's fine, but for HDR th

Lossless WebP is very good indeed. The main problem is that it is not very future-proof since it only supports 8-bit. For SDR images that's fine, but for HDR this is a fundamental limitation that is about as bad as GIF's limitation to 256 colors.

jug 3y ago
Ah, I didn't know this and I agree this is a fairly big issue and increasingly so over time. I think smartphones in particular hastened the demand for HDR quite a bit, what was once a premium/enthusiast feature you only had to explicitly buy into.
- fluidcruft 3y ago
  HDR is also important for medical imaging applications (which have been moving to web)
omoikane 3y ago
I haven't ran across websites that serves up HDR images, I am not sure I would notice the difference. WebP seems appropriately named and optimized for image delivery on the web. Maybe you are thinking of high bit depth for archival use? I can see some use cases there where 8-bit is not sufficient, though personally I store high bit depth images in whatever raw format was produced by my camera (which is usually some variant of TIFF).
- lonjil 3y ago
  8-bit can have banding even without "HDR". Definitely not enough. 10 bit HDR video is becoming more common, and popularity for images will follow. Adoption is hampered by the fact that Windows has bad HDR support, but it all works plenty well on macOS and mobile platforms.
  - adgjlsfhk1 3y ago
    unfortunately linux HDR is pretty much completely absent. That said, Wayland slowly looks like it's getting there.
    - toastal 3y ago
      X11 supports 10-bit SDR… which Wayland doesn’t
      - JyrkiAlakuijala 3y ago
        It would be nice if everything was non tone-mapped HDR all the time for software, and the windowing system or the monitor would do the (local) tone mapping.
        kllrnohj 3y ago
        No, you don't want that. You want your windowing system & UI/graphics layers working in display native range (see eg, Apple's EDR). The consistency of appearance of the SDR range is too important to leave it up to unknown tone mapping. Also it's too power expensive to have your display in HDR if you're only showing SDR UIs, which not only is the common reality but will continue to be so for the foreseeable future.
        JyrkiAlakuijala 3y ago
        I think both approaches have advantages. Requiring every game, photo viewing app, drawing program, ... every application to decide how to do it's HDR->SDR seems unnecessary complication due to poor abstractions. The locality of local tone mapping (the ideal approach to HDR->SDR mapping) would expose the window boundaries. Two photos or two halves of the same photo in different windows (as opposed to being in the same window) would create an artificial discontinuity for the correction fields being artificially contained within each window instead of spanning the users visual field as best as possible. Every local tone mapping needs to make an assumption of the surrounding colors: is the window surrounded by black, gray, colored or bright light should influence how the tone mapping is done at borders. This information is not available for an app: it can only be done at the windowing system level or in the monitor. The higher the quality of the HDR->SDR mapping in a system, the more opportunity there is to limit the maximum brightness, and thus also the opportunity for energy savings.
chungy 3y ago
Lossless WebP is also stuck with a low axis limit of 16383. It is a good format when you can use it, but JPEG XL almost always compresses better anyway, and lacks color space and dimension limits.
- JyrkiAlakuijala 3y ago
  This limit didn't exist in my first version as well as the 4 GB limit. These were artificially introduced to "match" the properties of lossy WebP. We could have done better there.
  - mardifoufs 3y ago
    Were you involved in creating WebP? If so that's super cool! Why would they want to match webp's lossy compression though? To make it more uniform? And do you know why lossy WebP had such a limitation in the first place? Thank you!
    - JyrkiAlakuijala 3y ago
      I designed the WebP lossless format, wrote the spec, and implemented the first encoder. The constraint was in WebP lossy to facilitate exact compatibility with VP8 specification and hoping that it would allow hardware decoding and encoding of WebP images using VP8 hardware. Hardware encoding and decoding were never used, but the limitation stuck. There was no serious plan to do hardware lossless, but the constraint was copied for "reducing confusion". I didn't and don't like it that much as more PNG images couldn't be represented as WebP lossless as a result of that.
      - chungy 3y ago
        Wow, that really sucks. I appreciate the explanation as well as your frustration with it. My desktop had a mixture of PNG and WebP files solely because of this limitation. I use the past tense because they've now all been converted to JPEG XL lossless.
kllrnohj 3y ago
For things where you actually care about lossless you probably also don't care about HDR. HDR is (or can be) good for video & photography, but it's absolutely ass for UI. Besides, you can just throw a gainmap approach at it if you really care. Works great with jpeg, and gainmaps are being added to heif & avif as well, no reason jpegxl couldn't get the same treatment. The lack of "true 10-bit" is significantly less impactful at that point
- JyrkiAlakuijala 3y ago
  Gainmaps don't solve 8-bit mach banding. If anything you get more banding: two bandings, one banding from each of the two 8-bit fields multiplied together. Gainmaps "solve" the problem of computing a local tone mapping by declaring that it needs to be done at server side or at image creation time rather than at viewing time. My prediction: Gainmaps are going to be too complex of a solution for us as a community and we are going to find something else that is easier. Perhaps we could end up standardizing a small set of local tone mapping algorithms applied at viewing time.
  - kllrnohj 3y ago
    > Gainmaps "solve" the problem of computing a local tone mapping by declaring that it needs to be done at server side or at image creation time rather than at viewing time. Which was already the case. A huge amount of phone camera quality is from advanced processing, not sensor improveds. Trying to get that same level of investment in all downstream clients is both unrealistic and significantly harder. A big aspect of why DolbyVision looks better is just Dolby forces everyone to use their tone mapping, and client consistency is critical. Gainmaps also avoid the proprietary metadata disaster that plaugues HLG/PQ video content. > If anything you get more banding: two bandings, one banding from each of the two 8-bit fields multiplied together. The math works out such that you get the equivalent of something like 9 bits of depth but you're also not wasting bits on colors and luminance ranges you aren't using like you are with bt2020 hlg or PQ
    - JyrkiAlakuijala 3y ago

jug 3y ago

Ah, I didn't know this and I agree this is a fairly big issue and increasingly so over time. I think smartphones in particular hastened the demand for HDR quite a bit, what was once a premium/enthusiast feature you only had to explicitly buy into.

fluidcruft 3y ago
HDR is also important for medical imaging applications (which have been moving to web)

omoikane 3y ago

I haven't ran across websites that serves up HDR images, I am not sure I would notice the difference. WebP seems appropriately named and optimized for image delivery on the web. Maybe you are thinking of high bit depth for archival use? I can see some use cases there where 8-bit is not sufficient, though personally I store high bit depth images in whatever raw format was produced by my camera (which is usually some variant of TIFF).

lonjil 3y ago
8-bit can have banding even without "HDR". Definitely not enough. 10 bit HDR video is becoming more common, and popularity for images will follow. Adoption is hampered by the fact that Windows has bad HDR support, but it all works plenty well on macOS and mobile platforms.
- adgjlsfhk1 3y ago
  unfortunately linux HDR is pretty much completely absent. That said, Wayland slowly looks like it's getting there.
  - toastal 3y ago
    X11 supports 10-bit SDR… which Wayland doesn’t
    - JyrkiAlakuijala 3y ago
      It would be nice if everything was non tone-mapped HDR all the time for software, and the windowing system or the monitor would do the (local) tone mapping.
      - kllrnohj 3y ago
        No, you don't want that. You want your windowing system & UI/graphics layers working in display native range (see eg, Apple's EDR). The consistency of appearance of the SDR range is too important to leave it up to unknown tone mapping. Also it's too power expensive to have your display in HDR if you're only showing SDR UIs, which not only is the common reality but will continue to be so for the foreseeable future.
        JyrkiAlakuijala 3y ago
        I think both approaches have advantages. Requiring every game, photo viewing app, drawing program, ... every application to decide how to do it's HDR->SDR seems unnecessary complication due to poor abstractions. The locality of local tone mapping (the ideal approach to HDR->SDR mapping) would expose the window boundaries. Two photos or two halves of the same photo in different windows (as opposed to being in the same window) would create an artificial discontinuity for the correction fields being artificially contained within each window instead of spanning the users visual field as best as possible. Every local tone mapping needs to make an assumption of the surrounding colors: is the window surrounded by black, gray, colored or bright light should influence how the tone mapping is done at borders. This information is not available for an app: it can only be done at the windowing system level or in the monitor. The higher the quality of the HDR->SDR mapping in a system, the more opportunity there is to limit the maximum brightness, and thus also the opportunity for energy savings.

chungy 3y ago

Lossless WebP is also stuck with a low axis limit of 16383. It is a good format when you can use it, but JPEG XL almost always compresses better anyway, and lacks color space and dimension limits.

JyrkiAlakuijala 3y ago
This limit didn't exist in my first version as well as the 4 GB limit. These were artificially introduced to "match" the properties of lossy WebP. We could have done better there.
- mardifoufs 3y ago
  Were you involved in creating WebP? If so that's super cool! Why would they want to match webp's lossy compression though? To make it more uniform? And do you know why lossy WebP had such a limitation in the first place? Thank you!
  - JyrkiAlakuijala 3y ago
    I designed the WebP lossless format, wrote the spec, and implemented the first encoder. The constraint was in WebP lossy to facilitate exact compatibility with VP8 specification and hoping that it would allow hardware decoding and encoding of WebP images using VP8 hardware. Hardware encoding and decoding were never used, but the limitation stuck. There was no serious plan to do hardware lossless, but the constraint was copied for "reducing confusion". I didn't and don't like it that much as more PNG images couldn't be represented as WebP lossless as a result of that.
    - chungy 3y ago
      Wow, that really sucks. I appreciate the explanation as well as your frustration with it. My desktop had a mixture of PNG and WebP files solely because of this limitation. I use the past tense because they've now all been converted to JPEG XL lossless.

kllrnohj 3y ago

For things where you actually care about lossless you probably also don't care about HDR. HDR is (or can be) good for video & photography, but it's absolutely ass for UI. Besides, you can just throw a gainmap approach at it if you really care. Works great with jpeg, and gainmaps are being added to heif & avif as well, no reason jpegxl couldn't get the same treatment. The lack of "true 10-bit" is significantly less impactful at that point

JyrkiAlakuijala 3y ago
Gainmaps don't solve 8-bit mach banding. If anything you get more banding: two bandings, one banding from each of the two 8-bit fields multiplied together. Gainmaps "solve" the problem of computing a local tone mapping by declaring that it needs to be done at server side or at image creation time rather than at viewing time. My prediction: Gainmaps are going to be too complex of a solution for us as a community and we are going to find something else that is easier. Perhaps we could end up standardizing a small set of local tone mapping algorithms applied at viewing time.
- kllrnohj 3y ago
  > Gainmaps "solve" the problem of computing a local tone mapping by declaring that it needs to be done at server side or at image creation time rather than at viewing time. Which was already the case. A huge amount of phone camera quality is from advanced processing, not sensor improveds. Trying to get that same level of investment in all downstream clients is both unrealistic and significantly harder. A big aspect of why DolbyVision looks better is just Dolby forces everyone to use their tone mapping, and client consistency is critical. Gainmaps also avoid the proprietary metadata disaster that plaugues HLG/PQ video content. > If anything you get more banding: two bandings, one banding from each of the two 8-bit fields multiplied together. The math works out such that you get the equivalent of something like 9 bits of depth but you're also not wasting bits on colors and luminance ranges you aren't using like you are with bt2020 hlg or PQ
  - JyrkiAlakuijala 3y ago