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RE: Color Management in HTML5?

From: Leonard Rosenthol <lrosenth@adobe.com>
Date: Sat, 6 Mar 2010 17:53:44 -0800
To: Maciej Stachowiak <mjs@apple.com>
CC: "L. David Baron" <dbaron@dbaron.org>, "public-html@w3.org" <public-html@w3.org>
Message-ID: <D23D6B9E57D654429A9AB6918CACEAA97CA6084E59@NAMBX02.corp.adobe.com>
_IF_ the HTML5 specification was only a file format description, then I would be in complete agreement with you - that color management is outside of scope.  BUT since the spec clearly stipulate quite exacting behavior (including algorithm implementation requirements) for many aspects of the implementation of a UA, then I have to disagree (strongly).   What makes the details of URL decoding any more important to be consistent in the UA than that of color management?

To your points.

CSS only applies to some elements on the page.  It does not apply to images or video, thus even if we were to accept that CSS dictates those elements that it impacts, there would still be limitations in the others.

> Typically, W3C and other specs seem to agree that the default colorspace is sRGB, though that is generally not implemented
That would seem to be a problem then, would you not agree?

As you know, the documentation for image formats(!) is just that - the file format.  The documentation for JPEG, PNG, etc. doesn't concern itself with rendering in any way - only the encoding and decoding of the pixel data (and associated pieces).   As such, those documents won't be relevant here.  However, if you look at the current section on <img> (http://www.w3.org/TR/html5/text-level-semantics.html#the-img-element) it talks about various things that a UA should do with the image and its data including some basics on how to "present it".  Seems like a logical addition here for CM.

If the correct procedure is the filing of bug reports, then I will report that back to the ICC and ask them to file the reports so that the various issues can be tracked and processed accordingly.  However, I wonder how the filing of reports will enable discussion by the committee on the topic at hand, since it seems like a fairly significant and far-reaching one.


From: Maciej Stachowiak [mailto:mjs@apple.com]
Sent: Sunday, March 07, 2010 10:31 AM
To: Leonard Rosenthol
Cc: L. David Baron; public-html@w3.org
Subject: Re: Color Management in HTML5?

On Mar 6, 2010, at 5:29 AM, Leonard Rosenthol wrote:

And this discussion is EXACTLY why the ICC wants to get involved.

As has been stated many times, the HTML5 spec is not only about the language & grammar BUT is also a set of requirements for UAs to ensure that all browsers render the same page in the same way.  As such, that includes not only that the right image goes in the right place on the page BUT that its colors are correct and match the colors shown in other browsers.

Nonetheless, most color management issues are not HTML issues. They are mostly an issue for CSS. I would say the most fruitful avenue for the ICC would be to coordinate with the CSS WG.

To accomplish this will mean that rules for color management within a browser need to be stipulated in the standard itself.   For example, the following (non-complete) list of questions need to answered...
*         What is the "default colorspace"?

This is not an HTML issue. It's an issue for individual specs that deal with color. Typically, W3C and other specs seem to agree that the default colorspace is sRGB, though that is generally not implemented (except perhaps on Windows where it's typical to assume that device color is approximately sRGB.)

*         How to handle embedded profiles in images (and possibly even how to look for them)

This is an issue for image format specs, or perhaps for a spec about how images should work on the Web.

*         How to handle CSS colors

That's an issue for the CSS spec.

*         How to handle SVG colors (which extend CSS a bit)

That's an issue for the SVG spec to the extent that it does not just defer to CSS.

*         Does Canvas need to be extended to deal with richer color (ala SVG)?

My interpretation would be that Canvas uses CSS colors and therefore should follow CSS rules about color. If the spec doesn't clearly say that, then that's a bug.

*         Does video need to be extended?

Would the correct process forward then be for the ICC to draft one or more formal & comprehensive Change Proposals (which will most likely be fairly widespread throughout one or more of the documents currently being authored)?

The correct first step to request a spec change for HTML5 would be to file a bug. A Change Proposal would be out of order.

In all fairness I should warn you that it's likely the bug would be rejected as out of scope for HTML.

Is it possible that some form of decision could be made to determine the "feelings" of the committee ahead of time?  I would hate to recommend to someone at the ICC that they invest the (huge) time necessary to draft such a document , only then to have it not approved.  Is there some sort of "pre-vote" or something that could be used in this case?

Even without a "pre-vote", a Change Proposal would be out of order without following the earlier steps in the process. And in any case, probably the best venue to make proposals would be the CSS WG, not the HTML WG.



From: Maciej Stachowiak [mailto:mjs@apple.com]
Sent: Saturday, March 06, 2010 7:15 AM
To: L. David Baron
Cc: Leonard Rosenthol; public-html@w3.org<mailto:public-html@w3.org>
Subject: Re: Color Management in HTML5?

On Mar 5, 2010, at 2:04 PM, L. David Baron wrote:

On Friday 2010-03-05 00:08 -0800, Maciej Stachowiak wrote:

Just to report on what Safari does: we colormatch images that are
tagged with an explicit colorspace, but we treat CSS colors and
colors in untagged images as being in the device color space
(instead of treating as sRGB). This seems to give a good balance
between performance for the common case and color-correctness for
cases where precise color is desired.

Gecko does this too (I think starting in Firefox 3.5?), but we got
quite a few complaints about it, and I'd like to change it.

It has the significant disadvantage that the relationships between
colors in different parts of the same page can be different
depending on the device (when a page has both tagged images and
other colors).

I think we should move towards treating CSS colors (and untagged
images) as sRGB, as CSS1, CSS2.1, and css3-color require.

Long-term, we would like to do this in Safari (treat CSS colors and untagged images as sRGB). In our attempts so far, there have been two blockers:

1) Our attempts to do this so far have resulted in significant performance regressions. We're still working on a way to do this with good enough performance.

2) We have no way to get plugins to participate in colormatching. We need additions to NPAPI to tell plugins whether to use device color or sRGB, and we need plugins to adopt them. This is especially critical for Adobe Flash, since there are pages that try to match static background colors or background images to Flash. We've had some discussions on this.

Received on Sunday, 7 March 2010 01:54:23 UTC

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