Problem with converting black from CMYK to RGB

[filipz35948559]

Hello everyone.

I have a problem which is a huge pain.

At my work, I often have to take the printing file and convert it to RGB, so I could put it in a mockup and show it to the client. My PC was only one in the office, that was able to do it right every time, getting always the same values of the black background. Unfortunately it WAS. Everything started when we've changed our default color profiles to work on Adobe 1998 instead of sRGB. I would completely understand, if those values would slightly change because of that, but they should stay constant for every file I make. Instead - weird stuff happens. For example - two very similar files (which have the same 100% K background, same fonts, just a different photo) tend to have completely different background color's values when converted to RGB - e.g. 71,73,64,81 and 78,76,61,81. Another interesting happens when i save the file as JPEG and reopen it. Before closing, color values appear to be 79,76,61,81, but when I close it and open it again, those values change to 80,76,60,80.

Does anyone have any idea why is this happening?

[c.pfaffenbichler]

For example - two very similar files (which have the same 100% K background, same fonts, just a different photo) tend to have completely different background color's values when converted to RGB

What are the two CMYK images’ Color Spaces?

when i save the file as JPEG and reopen it. Before closing, color values appear to be 79,76,61,81, but when I close it and open it again, those values change to 80,76,60,80.

When you decide to use lossy compression you have to accept its effects, maybe use tif with LZW or ZIP compression instead.

[filipz35948559]

I don't know if i understood you correctly, but the original files are PDF in Fogra27

[c.pfaffenbichler]

Could you provide the two files for testing?

Are you certain you used the identical conversion settings and that the color fields are indeed identical in the pdfs?

FOGRA27 is pretty much out-of-date by the way.

[filipz35948559]

I doubt it, my supervisors might not be OK with sharing it.

I'm pretty sure that I've used identical settings. I'm also 100% sure that there's no objects beneath the black background, since I've made the file myself.

FOR NOW I've managed to work out a procedure, that gives me the same results every time. Saving in Illustrator with color conversion  and including the profile, then converting in PS using Edit -> Convert to profile and saving to TIFF with ZIP as you've said (it did help with the difference after saving).

I'm just hoping that it's going to stay that way, because weird stuff happened since yesterday - the values I'm getting today are completely different from those I've had yesterday, even though I've tried many different conversion options today.

[c.pfaffenbichler]

Saving in Illustrator with color conversion  and including the profile, then converting in PS using Edit -> Convert to profile and saving to TIFF

When you convert the pdfs in Photoshop as CMYK do the affected black regions register the same values in the Info Panel?

[filipz35948559]

What do you mean exactly? Before converting there's 0,0,0,100, after there's 79,76,61,81. I was trying to get 78,76,61,81 after conversion but I've failed.

[c.pfaffenbichler]

One cannot »open« pdf in Photoshop, one can place them or convert them.

Do the resulting images, still in CMYK, definitely display the same CMYK values for the areas in question?

[filipz35948559]

yep, there's 0,0,0,100 as it should be

[c.pfaffenbichler]

Could you provide screenshots including the Convert to Profile-dialog for both converted pdfs?

Did you flatten the images before converting them to sRGB?

[filipz35948559]

As I said, since I've started using this "procedure" I described, I've managed to get the same results from both files. Gotta test this for a while and see how it goes. I'm still confused though - why today's results were different than yesterday's, even though I've tried the same methods and combinations... I have to be missing something. Earlier I didn't have to use any coversions, simply changing the mode worked perfect.

My Creative Suite is in Polish so screenshots might be tricky for you.

Long story short, for foth I have used: Source: FOGRA27, Target: Adobe RGB 1998, Mechanism: Microsoft ICM (Adobe ACE was giving results completely different than expected), method: relative colorimetric and checked the box "use black point compensation". I hope that's at least a bit accurate translation.

And by the way, You're saying FOGRA27 is pretty much out of date. What does that mean and what would You recommend?

[c.pfaffenbichler]

And by the way, You're saying FOGRA27 is pretty much out of date. What does that mean and what would You recommend?

FOGRA27 (aka ISO Coated) was superseded by FOGRA39 (aka ISO Coated v2) a while back and I would recommend going with that — unless your print provider specifically requests FOGRA27-separated files.

Actually FOGRA39 has been superseded by FOGRA51 (aka PSOcoated_v3), but I have the impression it has not been implemented widely yet.

[c.pfaffenbichler]

which have the same 100% K background

By default objects with 0/0/0/100 often overprint (when the default black has been used in Indesign for example).

So one possible explanation might be that there is a coloured object beneath the black object, to assess the original separations you could use Acrobat’s Output Preview with »Simulate Overprinting« checked.

[tmyusuf74]

Could you send me your file.