Image getting darker with 'export_profile' => 'srgb'

[goldmerc]

I'm using vips 8.14.1 and thumbnail_buffer. Following this advice...

https://www.libvips.org/API/current/Using-vipsthumbnail.html

I'm passing in 'export_profile' => 'srgb'

I notice that the thumbnailed images look darker. If I remove 'export_profile' => 'srgb' the thumbnail colour matches the original perfectly.

What's happening here? I could just remove 'export_profile' => 'srgb' but I want to understand whats happening in case I'm going to get different results with different images.

Thanks (as always!)

[jcupitt]

Hi again @goldmerc,

Do you have a sample image which shows this problem?

[goldmerc]

Hi @jcupitt :-)

Original Image...

This is optimised using newFromFile. The colour stays the same...

But when it gets thumbnailed (thumbnail_buffer), it's darker... (same with jpg + webp)

[goldmerc]

    'encoding_options' => [
        'jpg' => [
            'Q' => 85,
            'optimize_coding' => true,
            'interlace' => true,
            'strip' => true,
            'background' => "245 245 245",
        ],
        'webp' => [
            'Q' => 90,
            'strip' => true
        ],
    ]

[goldmerc]

If I remove 'export_profile' => 'srgb' from the thumbnail options, the colour stays as it should... (ie, not darker!)

[jcupitt]

Huh that's weird, it looks like lcms isn't roundtripping correctly. If I do:

$ vips copy k2.jpg x.jpg[strip]
$ vips icc_transform x.jpg y.jpg srgb

They don't match, but they should. I don't have time to investigate now, unfortunately, maybe next week.

[goldmerc]

Sure, no rush. I'll leave it with you as it's all beyond me!

[jcupitt]

Looks like this could be related: libvips/libvips#3150 (comment)

[kleisauke]

I confirm that using cmsFLAGS_NOOPTIMIZE would resolve this colour difference using the image in this discussion. Relevant PR: libvips/libvips#3368

[goldmerc]

Great - thanks both. So, will this fix be included in the next release? And when might we see that?
Thanks again for your help.

[jcupitt]

I'd guess in libvips 8.15, maybe summer 2023.

[kleisauke]

PR libvips/libvips#3373 targets the 8.14 branch, so this will be available in libvips 8.14.2 (RSN).