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?

  

[seans94943058]

OK, first of all thanks to all responders for their answers and patience. Ive been working with these files for 5 years and this is the first time I have had issues like this so assumed the color shifts had something to do with the source files which were coming in as "Linear' (see earlier in the conversation if you are just coming to the party).
To answer the layers question, we have always provided layered PSDs to the prodction artists who put these images on the packaging. This is because they like to turn the Shadows and Reflections ON and OFF (as needed) in InDesign which is apparently possible but I dont use InDesign so cannot comment. The images also need transparency so they can be placed on different backgrounds in the layout. I guess I will have to think of a workaround for that, any suggestions welcome.
I clearly need to understand Assign vs Convert and am trying to but frankly 'colot' just messes with my small brain.

[Stephen Marsh]

OK, if you need layered CMYK and you are converting without merging/flattening - then you will need to account for this hue shift in the reflection.

Edit: I'll kick this around and come back to you with some suggestions.

[c.pfaffenbichler]

To illustrate the absurdity of expecting CMYK transparency to provide identical results as RGB transparency I like to use the example of black at 50%. 

RGB (additive color) has true black, CMYK (subtractive color) does not. 

And that doesn’t even take into account the Total Area Coverage limitations in the various CMYK Spaces. 

[seans94943058]

Very helpful and thankyou.
Still unclear why SoftProofing does nothing in my file though.

[c.pfaffenbichler]

It seems to work fine on the image (see the difference in the blue »rollers«), but the transparency issue is another matter. 

[Stephen Marsh]

OK, if you need layered CMYK and you are converting without merging/flattening - then you will need to account for this hue shift in the reflection.

Edit: I'll kick this around and come back to you with some suggestions.

By Stephen Marsh

I tried various edits, in both RGB and CMYK and had the best results after conversion to CMYK, using selective colour on the reflection layer – reducing magenta in blues.

[NB, colourmanagement]

@seans94943058 "I clearly need to understand Assign vs Convert and am trying to but frankly 'colot' just messes with my small brain."

Assign profile - means

replace the file's profile label (the profile "tag"), this is required very rarely and almost always alters appearance, due to a change in interpretation of the image data by the colour engine.

The image pixel data is unchanged, but now incorrectly tagged

Convert to profile - means

translate the file's colour information to a new colourspace retaining image appearance*

(*within the limits of the destination gamut). 

The image pixel data is changed, to retain the appearance

A files profile tag provides information to the profile tag for any conversion, even sending data to the screen involves a conversion in the background, from file.icc to display.icc

you can see that is file.icc is changed the interpretation changes - since assigning replaces the right ICC profile with the wrong one that means the colour is messed up. As you have seen

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

[c.pfaffenbichler]

@Stephen Marsh clearly stated that you should flatten the image on conversion – did you do that?

 

[Stephen Marsh]

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

By D Fosse

If you convert a standard gamma profile image to 32-bit mode, a linear profile is created.

That being said, I would suggest using Color Settings, Custom RGB, gamma 1.0. This of course presumes that one knows the other values to enter, or can make an educated guess.

[NB, colourmanagement]

If the file IS displaying correctly in PS, then I guess it can't be untagged (because untagged files are displayed as if in the default working colour space as per color settings, probably sRGB or Adobe RGB? please check that)

- I am guessing that a correct profile must be already assigned or current appearance would be wrong

1: your issue is that you are assigning sRGB I think.

D Fosse is correct, you need to convert from a suitable document profile to sRGB.

Assigning an alternative ICC profile simply leaves the data unchanged but re-labels the image and the [now embedded] profile is then used in any outgoing conversion - e.g. as a source for display - assigning almost inevitably leads to changes to appearance. 

SO you need to convert to the desired colour space.

FROM a profile that suits the data 

As D Fosse asked, what's showing in "document profile", that’s where we see the embedded profile? 

If its NOT a linear profile then maybe you can set the image origination app to embed an ICC profile?

Otherwise, if you can't get a hold of a linear ICC profile to match the image production environment, then maybe convert to sRGB and apply a curve, that should be straightforward. 

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