[x3d-public] Need for colorspaceConversion field in ImageTexture, glTF compatibility

[Andreas Plesch]

Hi Don,

Here is the relevant glTF reference:

https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#images

"Any colorspace information (such as ICC profiles, intents, gamma values,
etc.) from PNG or JPEG images *MUST* be ignored. Effective transfer
function (encoding) is defined by a glTF object that refers to the image
(in most cases it’s a texture that is used by a material)."

There may be an github issue discussing this decision as well.

Best regards,

Andreas

On Thu, Sep 21, 2023, 6:54 AM Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>
wrote:

> Thanks for an interesting candidate capability.  Some references:
>
>
>
>    - Wikipedia: Color space
>    - https://en.wikipedia.org/wiki/Color_space
>
>
>
>    - Wikipedia: List of color spaces and their uses
>    - https://en.wikipedia.org/wiki/List_of_color_spaces_and_their_uses
>
>
>
> From glTF 2.0
>
>
>
>    - 3.9.3. Additional Textures
>    - emissive : The emissive texture and factor control the color and
>    intensity of the light being emitted by the material. The texture MUST
>    contain 8-bit values encoded with the sRGB opto-electronic transfer
>    function so RGB values MUST be decoded to real linear values before they
>    are used for any computations. To achieve correct filtering, the transfer
>    function SHOULD be decoded before performing linear interpolation.
>    -
>    https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#additional-textures
>    - References
>    - IEC 61966-2-1 *Default RGB colour space - sRGB*
>    https://webstore.iec.ch/publication/6169
>
> Note
>
> The encoding characteristics of sRGB are freely available from ICC:
> https://www.color.org/chardata/rgb/srgb.xalter
>
>    - (which is at International Color Consortium)
>
>
>
> Additional references welcome
>
>
>
> Each mention of color profile that I found in glTF indicated that SRGB
> profile usage was required.  Didn’t see any other options.  Wondering if
> there is further work in glTF extensions on this topic.
>
>
>
> Prior attempts to permit gamma definition in X3D did not converge on an
> acceptable solution.
>
>
>
> I did not find relevant mention of “color space” or “SRGB” in X3D 4.0
> specification.
>
>
>
> If we can align with other standards, particularly glTF evolution, then
> this field certainly seems like a candidate to become a Web3D Consortium
> Recommended Practice in anticipation of future X3D 4.1 Architecture.  No
> doubt we would want to look carefully across the specification to ensure
> that color was handled consistently and interoperably.
>
>
>
> Continued scrutiny and development welcome.  Have fun with X3D color
> control!  8)
>
>
>
> all the best, Don
>
> --
>
> Don Brutzman  Naval Postgraduate School, Code USW/Br
> brutzman at nps.edu
>
> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
> +1.831.656.2149
>
> X3D graphics, virtual worlds, navy robotics
> https://faculty.nps.edu/brutzman
>
>
>
> *From:* x3d-public <x3d-public-bounces at web3d.org> *On Behalf Of *Holger
> Seelig
> *Sent:* Thursday, September 21, 2023 3:06 AM
> *To:* Andreas Plesch <andreasplesch at gmail.com>
> *Cc:* X3D <x3d-public at web3d.org>
> *Subject:* Re: [x3d-public] Need for colorspaceConversion field in
> ImageTexture, glTF compatibility
>
>
>
> I have now also added the field `colorSpaceConversion` in X_ITE to the
> ImageTexture node, also in the same notation. Everything was already
> prepared for it.
>
>
>
> I can't show an example yet, because everything is still in the dev branch.
>
>
>
> The signature of the new field looks like this:
>
>
>
> SFBool [] colorSpaceConversion TRUE
>
>
>
> Best regards,
>
> Holger
>
>
>
> --
>
> Holger Seelig
>
> Leipzig, Germany
>
>
>
> holger.seelig at yahoo.de
>
> https://create3000.github.io/x_ite/
>
>
>
> Am 21.09.2023 um 08:26 schrieb Andreas Plesch <andreasplesch at gmail.com>:
>
>
>
> Coming back to color profiles potentially embedded in some important
> image formats, I added a colorSpaceConversion field to ImageTexture in
> x3dom:
>
>
> https://andreasplesch.github.io/x3dom/dist/doc/author/Texturing/ImageTexture.html
>
> It is by default true for normal X3D use and can be false for loading
> glTF textures correctly:
>
>
> https://andreasplesch.github.io/Library/Viewer/index.html?url=https://gist.githubusercontent.com/andreasplesch/817bc44089a7b7545149cf12acdd7c86/raw/75242ebfea03048d0f4939e1656c5063c9544d11/TextureEncodingTest.x3d
>
> It is trivial to change the field name if there are other suggestions.
>
> -Andreas
>
> On Tue, Aug 29, 2023 at 1:53 PM Andreas Plesch <andreasplesch at gmail.com>
> wrote:
>
>
> Following up after some work:
>
> On Thu, Aug 24, 2023 at 11:15 PM Andreas Plesch <andreasplesch at gmail.com>
> wrote:
>
>
> On Thu, Aug 24, 2023 at 9:14 AM Michalis Kamburelis
> <michalis.kambi at gmail.com> wrote:
>
>
> 1. As for colorspaceConversion:
>
> I don't think we want to avoid adding X3D field for this :)
>
>
> Well, it is worth thinking through options if it means smarter
> solutions can be discovered.
>
>
> I'm all after adding X3D field to account for this -- that is, say
> explicitly whether ICC profile should be honored or not, so that all
> cases are satisfied. I'm cool with colorspaceConversion name.
>
>
>
> ...snip
>
> After some thought I do think that a new field is needed for
> ImageTexture (and MovieTexture, and Background ?).
> "colorspaceConversion" or "colorSpaceConversion" or perhaps something
> shorter like "colorProfile"  ?
>
> x3dom will probably use the webgl texture unpacking parameter.
>
>
>
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