[webkit-dev] canvas and sRGB

[Rik Cabanier]

On Mon, May 2, 2016 at 2:59 PM, Dean Jackson <dino at apple.com> wrote:

>
> On 3 May 2016, at 7:04 AM, Rik Cabanier <cabanier at gmail.com> wrote:
>
>
>
> On Mon, May 2, 2016 at 1:58 PM, Simon Fraser <simon.fraser at apple.com>
> wrote:
>
>> On May 2, 2016, at 1:45 PM, Rik Cabanier <cabanier at gmail.com> wrote:
>>
>> All,
>>
>> with the release of DCI-P3 screen, WebKit began supporting the display of
>> high gamut images.
>> Specifically, if you have an image with a DCI-P3 profile, its pixels
>> render untouched on the new displays.
>>
>> However, if you try do do any sort of canvas manipulation, you will see
>> that the colors are being compressed to sRGB and you will lose the depth of
>> the color.
>>
>> Was it an oversight to always create the canvas imagebuffer in sRGB? [1]
>>
>>
>> No, this was a deliberate choice. We can't change author expectations for
>> what getImageData() return.
>>
>
> Now we see different visual output which is also not what an author
> expects :-(
>
>
> Since there is no way to create a canvas element with pixel data that is
> interpreted to be in anything other than sRGB, this behaviour seems
> expected to me. I'm not sure what else could happen? We couldn't magically
> make all the canvas elements in the page use P3. If we did that, they
> wouldn't match the CSS content.
>

I don't see why that would be. CSS colors and tagged/untagged images would
be color corrected while being drawn just like it happens in HTML.
get/putImageData would of course be uncorrected as it works on raw pixels.


> The fix is coming: a way to tag the colorspace of the canvas element.
>

That's great! Do you have an idea how far off that proposal is?


> Can you elaborate what is unexpected with getImageData? Is it that css
> "red" no longer returns 100% red pixels?
>
>> If this is as-designed, how can we work around this limitation?
>>
>>
>> With possible future enhancements to the canvas spec that allow authors
>> to request backing store with a different format and/or color profile.
>>
>>
>> PS
>> I asked the same question on WhatWG. [2]
>>
>>
>> 1:
>> https://github.com/WebKit/webkit/blob/112c663463807e8676765cb7a006d415c372f447/Source/WebCore/platform/graphics/ImageBuffer.h#L73
>> 2:
>> https://lists.w3.org/Archives/Public/public-whatwg-archive/2016Apr/0036.html
>>
>>
>> Simon
>>
>>
>>
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