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Re: [Public WebGL] lossless texture uploading

On Wed, Nov 17, 2010 at 4:50 PM, Gregg Tavares (wrk) <gman@google.com> wrote:
> On Wed, Nov 17, 2010 at 4:05 PM, Mo, Zhenyao <zhenyao@gmail.com> wrote:
>> During the implementation of COLORSPACE_CONVERSION setting in webkit,
>> I began to think that maybe COLORSPACE is not the correct word for the
>> issue.  What we want is the raw bits from the image data, ignoring all
>> the settings in the image header (meta data).  Color space only covers
>> one of those settings.  Others include gamma, image orientation, and
>> who knows what might be added in the future?
> I noticed this as well. The original intent was to provide a way to get
> exact binary data from lossless image formats into a WebGL into a texture.
> For PNG that means ignoring the sRGB, iCCP, cHRM, gAMA chucks.
> But the new UNPACK_COLORSPACE_CONVERSION_WEBGL pixelStore setting only
> mentions that colorspace will not be applied. It mentions nothing about
> gamma or other settings that might end up changing the values uploaded to
> the texture and it mentions nothing about only caring about lossless images.
> The implication is that colorspace settings should also be ignored in JPEGs
> as well.
> I thought the goal was to specify a way to guarantee, cross browser, that
> loading certain kinds of images into a WebGL textures would have the exact
> same binary values passed to glTexImage2D and related functions.
> Should we update the spec and/or the name of the enum to make that clearer?
> or maybe just changing the description of UNPACK_COLORSPACE_CONVERSION_WEBGL
> to cover the goals?

The wording in the spec is intentionally vague because some of the
authors (like me) aren't well versed in all of the parameters of these
files. That having been said, while JPEGs aren't useful for uploading
data losslessly to WebGL, if we have an option for passing through PNG
files' data without applying an ICC color profile then I think it
might as well apply to JPEG files as well. At least in the WebKit
implementation, Mo has wired up the flag to both JPEGs and PNGs.

Personally I think the current wording is fine and we can supplant
this flag with another more tightly defined one in a future version of
the spec if necessary.


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