Converting Linear images to sRGB

[seans94943058]

Let me start by saying I struggle to understand color profiling and such so this question may seem obvious to some of the more enlightend amongst you.

I am processing 3D renders that are coming to me as 16-bit TIFFs in Linear Color Space. When I assign sRGB to the images they get very dark.

For confidentiality reasons I cannot sure much more of the image I am afraid.

Is there a method to assign/convert to sRGB without this dramatic color shift?

  

[D Fosse · Accepted solution]

Is there an embedded icc profile in the file now? If there is, convert to sRGB. That remaps the tone curve and there won't be any visual change.

If there isn't, this is getting a bit more tricky. Then you first need to find a linear gamma profile with the right primaries and white point, and assign that. Then you can convert to sRGB.

I've never had any use for linear profiles, so I don't know where you'd find that.

What does it say here:

[seans94943058]

How can I tell if there is an embedded profile?
This is what the Document Profile currently displays:

[TheDigitalDog]

That screen captures hows indeed, it's in a "Linear Color Space (16-bits") but that seems an odd name for such a profile. 

DO NOT ASSIGN sRGB to this data, convert to sRGB. There should be no such color shift thereafter doing it this way. 

[D Fosse]

OK, then try to convert to sRGB IEC61966-2.1.

If that linear profile is a valid icc-spec profile, that conversion should result in no visual change. It should then be remapped to the sRGB tone curve (and sRGB primaries).

[seans94943058]

So converting to sRGB does indeed produce no visual change so I cannot thank you all enough for this. However, after doing all our retouching in RGB, our workflow then calls for us to merge layers, rasterize smartobjects etc and convert to CMYK GraCOL.
I know that colors can shift when doing this but I'm a little puzzled why the Relection in my scene is shifting so much dramatically than the actual product which is essentially made up of the same colors.

sRGB:



CMYK:

[D Fosse]

You have to flatten and rasterize everything before converting to CMYK. You can only have flat pixel layers, no transparency, no blend modes, no adjustment layers.

I don't know how the reflection was made, but the "main" blue color is out of gamut in CMYK. It cannot be reproduced with process inks on paper. So it will shift somewhat when converted. If it's a solid color at low opacity it will still be out of gamut. Smart objects may keep their original color space, but will output rasterized and so in the master color space.

[TheDigitalDog]

It is 'shifting' thanks to the CMYK (color gamut) etc. And we're assuming this CMYK output profile is correct, ideal etc. 

[Stephen Marsh]

I know that colors can shift when doing this but I'm a little puzzled why the Relection in my scene is shifting so much dramatically than the actual product which is essentially made up of the same colors.

sRGB:



CMYK:

By seans94943058

You're going to need to reduce magenta in the blue reflection only to keep the reflection blue rather than purple. Much easier to do this in RGB with a CMYK GRACoL softproof than doing it in CMYK.

[seans94943058]

Softproof? But we have to deliver CMYK images for print.

[TheDigitalDog]

Soft proof, make output-specific edits (if necessary or desired) IN RGB using the CMYK profile for output (as an option....) before conversion: 

http://digitaldog.net/files/SoftProofingInPhotoshopCC.mp4

[Stephen Marsh]

Softproof? But we have to deliver CMYK images for print.

By seans94943058

Sorry, I thought that it was obvious. Make any edits, non-destructive or in a copy of the master RGB file, that are specific to the GRACoL condition, while in RGB using the GRACoL softproof, before finally converting to GRACoL.

EDIT: I just tested with your screenshot using different GRACoL 2006 Coated profiles and didn't see such a drastic hue shift in the reflection, perhaps because your GRACoL profile or conversion options are different or that I'm working on a sRGB screenshot and not the original which might be Adobe RGB or ProPhoto RGB etc.

[seans94943058]

Great tip, thanks Stephen and DigiDog. The screenshot you converted to GraCOL will not show a drastic shift because that is a flat image. In  my original image the Reflection and the Shadow are on layers. There is something about the layers which is casuing the shift.

[Stephen Marsh]

---

seans94943058 wrote:

Great tip, thanks Stephen and DigiDog. The screenshot you converted to GraCOL will not show a drastic shift because that is a flat image. In  my original image the Reflection and the Shadow are on layers. There is something about the layers which is casuing the shift.

---

Layered files need to be flattened/merged before or during conversion to CMYK as the blend mode or opacity layering in RGB doesn't "translate" into CMYK mode the same way when layers are preserved.

[seans94943058]

So I tried the SoftProofing and did a side-by-side comparison with a conversion to CMYK/Assign GRACol. Weirdly the SoftProofing does not show the color shift.

[Stephen Marsh]

So I tried the SoftProofing and did a side-by-side comparison with a conversion to CMYK/Assign GRACol. Weirdly the SoftProofing does not show the color shift.

By seans94943058

On a copy, flatten first, then convert or convert with flatten on. This should then match the softproof.

[TheDigitalDog]

You see no difference because according to the Proof Setup screen capture, the document is GRACol as is the soft proof. 

And you really need to get clear the huge difference between Assign vs Convert:

http://digitaldog.net/files/06AssignProfileCommand.pdf

[seans94943058]

Sorry DigitalDog, I'm confused, the image on the right is sRGB with the GRACol softproof applied. The image on the left is CMYK with the GRACol profile assigned

[c.pfaffenbichler]

Who said you should assign the profile? 

If by »a conversion to CMYK/Assign GRACol« you mean you converted the image to your Working CMYK Space and then assigned the intended profile then that would have been Color Management-wise nonsense. 

[seans94943058]

I go to Image->Mode->CMYK Color, then Assign GRACoL.

[c.pfaffenbichler]

I go to Image->Mode->CMYK Color, then Assign GRACoL.

By seans94943058

That is wrong (unless the intended CMYK Space is coincidentally also the CMYK Working Space). 

Please convert the flattened copy of the image to the correct target space (Edit > Convert to Profile). 

[TheDigitalDog]

I go to Image->Mode->CMYK Color, then Assign GRACoL.

By seans94943058

That is all wrong: sorry.

Again; you need to understand the Assign Profile Command and when to rarely use it!

[NB, colourmanagement]

@seans94943058  "I go to Image->Mode->CMYK Color, then Assign GRACoL."

Definitely don't do that, go to convert to profile and set the destination ICC profile to the correct GRACoL variant.

Why? Assigning misinterprets your file data. 

IF your working CMYK was GRACoL, that would be fine, but what you are doing is like translating a book into French, then adding a German sleeve or label to it, it's now labelled incorrectly and will be interpreted incorrectly. 

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

[seans94943058]

Here is the file in question:

[Stephen Marsh]

Here is the file in question:

By seans94943058

The file is OK, the problem is the conversion to CMYK while retaining the layers. Again, flatten during conversion or beforehand in a copy.

Why do you wish to have a CMYK file with layers? In this case, what benefit does it provide? The downside is obvious.

The RGB file should be considered the working file (layered), while the CMYK copy is a flattened derivative solely for output.

I am not saying that layered CMYK working files have no validity... Just trying to understand why you are converting without flattening.