Unexpected change in colorconvert() output between OIIO 2.3.13 and 2.5.7

[Maxi741cv]

Original (OpenImageIO 2.3.13.0-1)

>>> spec.nchannels = 4   format = ColorSpace="sRGB"
>>> before raw pixel RGBA = 1, 0, 0, 1
OIIO::ImageBufAlgo::colorconvert(buf, buf, "srgb", "linear", false);
>>> after raw pixel RGBA = 1, 0, 0, 1

Now (OpenImageIO 2.5.7.0-1)

>>> spec.nchannels = 4   format = ColorSpace="sRGB"
>>> before raw pixel RGBA = 1, 0, 0, 1
OIIO::ImageBufAlgo::colorconvert(buf, buf, "srgb", "linear", false);
>>> after raw pixel RGBA = 0.613281, 0.0701904, 0.0206146, 1    // here’s the difference, wtf?

[Maxi741cv]

Upd: This only fails on Windows; on Ubuntu 24 it works fine.

[lgritz]

Maybe it's a function of whether OIIO was build with OpenColorIO support or not? Or, if OCIO is there, whether or not an OCIO config was found at runtime?

This was all a bit of a mess in those older versions. Starting with OIIO 3.0 (which is the currently supported version), OCIO is a mandatory dependency, and it can also fall back on OCIO's built-in configs if no external one is found. So there is (in addition to other improvements) a lot more uniformity from platform to platform and build to build.

[Maxi741cv]

OIIO was taken from msys2 and, as far as I can tell, it was built with OpenColorIO support. No changes were made to the code. Thanks, I’ll check the behavior and try updating to version 3.0.

[Maxi741cv]

Excuse me, @lgritz, could you help?

My OCIO config differ. Is there a way to make colorconvert behave consistently?

OpenImageIO 2.3.13.0-1

OCIO config path: 'built-in'
OCIO error: '1'
Color spaces: 6
linear
default
rgb
RGB
sRGB
Rec709

OpenImageIO 2.5.7.0-1

OCIO config path: 'ocio://default'
OCIO error: '0'
Color spaces: 23
sRGB - Display
Display P3 - Display
Rec.1886 Rec.709 - Display
Rec.2100-PQ - Display
ST2084-P3-D65 - Display
P3-D65 - Display
ACES2065-1
ACEScc
ACEScct
ACEScg
sRGB Encoded Rec.709 (sRGB)
Gamma 1.8 Encoded Rec.709
Gamma 2.2 Encoded Rec.709
Gamma 2.4 Encoded Rec.709
sRGB Encoded P3-D65
Gamma 2.2 Encoded AdobeRGB
sRGB Encoded AP1
Gamma 2.2 Encoded AP1
Linear Rec.709 (sRGB)
Linear P3-D65
Linear AdobeRGB
Linear Rec.2020
Raw

[Maxi741cv]

I think I’ve probably found exactly what needs to be done correctly. Is that right?

Before:

const char* fromspace  = "srgb";
const char* tospace = "linear";
OIIO::ImageBufAlgo::colorconvert(buf, buf, fromspace, tospace, false);

After:

const char* fromspace  = "sRGB - Display";
const char* tospace = "Linear Rec.709 (sRGB)";
OIIO::ImageBufAlgo::colorconvert(buf, buf, fromspace, tospace, false);

[lgritz]

It looks like your OIIO 2.3 is either not built against OCIO at all, or if it is, then it was unable to find any "config" file externally, so it's just kind of hacking things up with a couple fake color spaces.

Your OIIO 2.5 was built with OCIO support, and in particular, a new enough version of OCIO that it has an "internal default config" it can fall back on even if no external config file is found.

So I believe that if you explicitly specify the names of the found color spaces, like you show above, you should get the correct and consistent results.

Starting with OIIO 3.0, it switched from OCIO being an optional dependency to a required one, and it must be an OCIO new enough to support the built-in configs. So there is a lot less random behavior variation possible now.