Suspicious Results using Lightroom Soft Proofing

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  • Updated 3 years ago
I noticed unexpected Destination Gamut Warnings when checking a Granger Chart with an embedded sRGB colour profile.

WIth the Soft Proofing profile set to sRGB (perceptual intent), one would expect that all image colours would be included the colour space and, therefore, that there should be no gamut warnings. This is clearly not the case as shown in the attached screenshot.

Can anyone explain this behaviour or is this a deficiency in the Lightroom Soft Proofing feature itself?

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Lightshiner

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Posted 3 years ago

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Steve Sprengel, Champion

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Some of an sRGB Granger chart is even outside of ProPhotoRGB's gamut according to LR CC's Softproof:


The chart came from the zip file on this page:
http://www.martinbaileyphotography.co...
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Lightshiner

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Click here to link to the Granger Chart sRGB IEC 61966-2.1 (Copyright 2011© Douglas Janson) that was used for my test.
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Lightshiner

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Thanks Steve.

If you have a moment, could you check to see if the chart was generated correctly (see How to Create Color Test Charts?

Also, is there any way to confirm that the image's embedded sRGB profile is correct?
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Lightshiner

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Lightshiner

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Further experimentation has revealed additional unexpected behaviour with regards to Monitor Gamut Warnings (see The Luminous Landscape forum post: Granger Chart Soft Proofing Anomalies? for details).
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LRuserXY

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The monitor gamut warning is implemented _after_ the conversion to the target color space, so if both are equal, there will be no monitor warning regarless of the original saturations.

This was changed in some early beta (?) stage when the softproof was introduced, and I think there was an explanation by Eric Chan why this was changed in the Adobe forums. Unfortunetely, this was never explained in Adobes official Lightroom help/documentation.

Edit: Found it: https://forums.adobe.com/thread/94740... (Jao vdLs post and Eric Chans answer "The current behavior is a bug and will be fixed").

It seems logical, because if I want to softproof using a printer profile, I am not interested in the areas that exceed the monitor gamut in the _original_ image. I am only interested in the areas that exceed the monitor gamut in the _converted_ image - because only these areas will _not_ look the same on the monitor vs. printed out.

P.S. Perhaps you can add this info to the LuLa discussion if you want... I have no account there (yet)...
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Lightshiner

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LRuserXY,

Thank you very much for providing this explanation as well as for the pointer to the related forum thread. While this explains the observed behaviour, I have to say that the available documentation should be made much more precise.

Perhaps you can shed some light on the other behaviour that I flagged as suspicious. Why would an image than conforms to a particular colour space (with the profile embedded) exhibit Destination Gamut Warnings when Soft Proofing is set to the identical profile?

Regards,

David
P.S. I'll cross post your response to The Luminous Landscape forum.
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LRuserXY

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I can't explain the other behaviour (the gamut warnings in the sRGB granger chart). It looks suspicious to me as well. If I remember correctly, I have seen this behaviour some time ago with a different "full gamut" sRGB chart.

PS Yes, the LR documentation is not very precise. For instance, I just learned that the _local_ defringe slider has slightly different meanings for negative and positive values. As far as I know this is nowhere mentioned in the "official" documentation. Instead, I learned it in this excellent article: http://blogs.adobe.com/lightroomjourn.... I think we need more articles like this as part of the help system.
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LRuserXY

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Strange: The gamut warning changes when you turn the GPU accelleration on and off. With GPU enabled, more gamut warnings are shown than without.

For instance, pure sRGB green (0, 255, 0) shows without warning when the GPU accel. is off, but with warning when it is on.

Note: There is also something wrong with the RGB-Values in the histogram when the softproof is enabled. I will post a separate problem for that. See here: http://feedback.photoshop.com/photosh...
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Lightshiner

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Thanks LRuserXY.

I tried toggling the GPU on and off and can confirm that I observed differences in the gamut warnings with the Granger Chart.

Perhaps this difference is evidence, more generally, that there is variation in the way LR characterizes colour. If so, could the unexpected gamut warnings possibly be explained by LR using (slightly) different methods for interpreting an embedded profile versus the profile used by Soft Proofing?

- David
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Lightshiner

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I discovered a simply test case which illustrates the problem with GPU assisted Soft Proofing. The issue identified seems to be related to the transition between colours (see below).

Note the the attached JPEG test chart is not identical to the TIFF version used in my testing (TIFF available at https://drive.google.com/file/d/0Bynl...)

- David