Generative expand not honouring cmyk values

[daytona_74]

Help needed please; Generative Expand is an excellent feature and is saving me loads of time and the results are excellent, however the new Generative Expanded part created has different CMYK values to the rest of the image area which will effect final print output. My current image only requires CMY but the extended part now has Black added, so not ideal. I've tried converting to RGB before Generative Expand but thats not working either. Ideas apprecitaed.

Thank you!

[Stephen Marsh]

I've tried converting to RGB before Generative Expand but thats not working either.

By @daytona_74

What do you mean exactly by this?

[daytona_74]

Well, I've epeanded an image with Photoshop's Generative Expand and the CMYK values have changed in the channels on the extra part. I.e. Black was not part of the image but it is now. I have a CMY image as it is light and colourful and works without K (Black) and prints successfully too - thanks!

[Stephen Marsh · Accepted solution]

That didn't clarify anything for me...

I presume that when you convert your CMY(K) image to RGB,  then Generative Expand, and then convert back to CMYK mode – then you find that K has been introduced when it wasn't there beforehand.  If so, this is expected unless your CMYK profile has no black generation.

What you can do is start with your CMY(K) file, then use Image > Mode > Multichannel, delete the blank 4th black channel, then Image > Mode > RGB. Run Generative Expand. Then Image > Mode > Multichannel, add a 4th white/blank channel, then Image > Mode > CMYK. This should retain the original CMY channel values and structure as you are bypassing ICC colour management. The caveat is that layers will be flattened when going through multichannel mode.

[daytona_74]

The image is CMY(K) to start with and all I am doing is expanding the image and getting incorrect CMY(K) values in the newly expanded part. This is not expected and probably a bug in the software. Would you suggest in your second paragraph could be a work around if successful although a lot of work and might as well do the cloning manually until the software is ironed out 🙂 Thanks!

[Stephen Marsh]

The image is CMY(K) to start with and all I am doing is expanding the image and getting incorrect CMY(K) values in the newly expanded part.

Understood and although unwanted, this isn't surprising to me.

The Firefly training data would be RGB (I'm taking an educated guess).

This is essentially the same scenario of having a CMYK file that has a custom black generation, that you convert to RGB and then back to CMYK  again and get different CMYK values afterwards.

The generative process is drawing on RGB data, and then converting to to your document or working space CMYK profile on the fly.

Perhaps if you had a CMYK document profile or working space that had no black generation, then you wouldn't get K introduced into the image, but the CMY values may still be off (untested).

We don't desaturate in CMYK mode as the algorithm has no idea about non-linear grey balance throughout the tonal range. We do "creative" things in RGB... And perhaps you should think of generative features in a similar way.

...you suggest in your second paragraph could be a work around if successful although a lot of work and might as well do the cloning manually until the software is ironed out 🙂 Thanks!

By @daytona_74

A simple action for the CMYK to RGB and RGB to CMYK multichannel conversion only takes a second or two to run.

[D Fosse]

Undesirable in this particular case, but not unexpected.

The software running on Adobe's servers in all likelihood works strictly with RGB data, and then reconvert to the original color space when sent back to the user. Any profile conversion into CMYK will output 4 channels that are recalculated from Lab/XYZ (the profile connection space).

CMYK is a tiny niche already. Your K channel may be empty, but it's still technically a CMYK file.

You can post this as a feature request, but be prepared that this will be low priority due to very limited use.

Stephen's workaround is your best bet.

[daytona_74]

What you can do is start with your CMY(K) file, then use Image > Mode > Multichannel, delete the blank 4th black channel, then Image > Mode > RGB. Run Generative Expand. Then Image > Mode > Multichannel, add a 4th white/blank channel, then Image > Mode > CMYK. This should retain the original CMY channel values and structure as you are bypassing ICC colour management. The caveat is that layers will be flattened when going through multichannel mode.

By @Stephen Marsh

Pleased to report that this work around for keeping CMYK values worked! When working in the print industry, we have to be mindful of print consistency and thats why it was so important to get this right - thank you!