Conversion to Black Ink - CMYK for print purposes

[sd5e8a]

I'm currently making grayscale-to-CMYK Black conversions in Photoshop.

Since the images are intended for 1-color offset printing, they have to use the Black Ink of the CMYK profile required by the printery (for example "Black Ink - Fogra XY").

After the conversion, I'm comparing the resulting image with the original one. I temporarily assign profiles to both of them and then they look the same.

But then I discovered that these "Black Ink" images are (mis?)represented in Photoshop as 4-color CMYK images. When I check the CMY plates in Photoshop, they are not empty. Or maybe I'm misunderstanding something?

Regardless of this, after I save these images and after I use them in Indesign, Acrobat's Output Preview shows them as using the black plate only (C=0, M=0, Y=0). So it seems that this works fine, but I'm not sure. Maybe I'm missing something important?

I also made the following experiment: in Acrobat I converted the grayscale content to CMYK with these options checked: "Preserve Black" and "Promote Gray to CMYK Black". Then I opened one of the images for external editing in Photoshop, and the CMY plates were just empty (white), while the whole content of the image was on the black plate. This is what I want, but there's a problem. In this case the content is considered CMYK and not Gray, which might create confusion (for example: what if you decide to tweak your PDF by targeting the grayscale content only? There will be no more content identified as grayscale, but only CMYK).

Thanks for your advices in advance

[Chris 486]

Hi @sd5e8a !

Thank you for the detailed description here. It sounds you are getting the results that you were hoping for with grayscale to cmyk conversion.

Your Printer is asking for a cmyk output. That seems to be your end goal correct? It's seems to have met that in you description. What are you looking to go back to grayscale for after?

[barbara_a]

If you want only the black channel of CMYK to have information, in the original grayscale image, you could Select All and Copy the Gray channel in the Channels panel. Then convert the grayscale image to CMYK. Target only the K channel and Paste. Then target the C, M, and Y channels one at a time and fill them with white.

[D Fosse]

If they are 4 color in Photoshop, you have converted to CMYK. That's not what you should do.

You can either convert to grayscale Black Ink - FOGRAxx, and place that directly in InDesign. It will be treated as 0-0-0-K, and output on the black plate only.

Or you can create a new FOGRAxx CMYK file, and paste your Black Ink - FOGRAxx grayscale into the K channel. That will be treated as a perfectly standard CMYK file, but as it happens with content only in the K channel.

The net end result should be the same in these two cases, and they should both be correct.

[Stephen_A_Marsh]

Without providing screenshots that have the appropriate panels and info, or providing sample images it is hard to comment on what you describe.

[sd5e8a]

You can either convert to grayscale Black Ink - FOGRAxx, and place that directly in InDesign. It will be treated as 0-0-0-K, and output on the black plate only.

By @D Fosse

Thanks, that's exactly what I'm doing.

I go to Color Settings > Load Gray > Fogra XY and I get Black Ink - Fogra XY in the list. Then I go to Edit > Convert Profile and I convert the image to Black Ink - Fogra XY.

The resulting image is identified as Gray/8, not CMYK. It is assigned an ICC profile (Black Ink - Fogra XY).

Then, if I go to Window > Info and if I set the Eyedropper tool to Actual color, it shows K values only. So everything seems to be fine.

The question is why this happens: if I go to View > Proof Setup to take a look at the plates, View > Proof Colors is automatically checked and the image is represented as if it is a 4-color CMYK. The CMY plates are not empty.

I also tried to customize the proof setup by setting it to Black Ink - Fogra XY, but it doesn't help or maybe I'm doing something wrong.

I also made an experiment by converting the images to Dot Gain %, but I get the same thing.

Regardless of all that, these Black Ink images seem to work just fine in Indesign and Acrobat. They output on the K plate only (as I can see in Acrobat's Output Preview).

The conclusion seems to be: there's nothing wrong with the resulting image, its just it is represented as 4-color CMYK in Photoshop's proof preview.

Why this happens and how to set it right - I don't know, but it seems that I can safely ignore it.

Or you can create a new FOGRAxx CMYK file, and paste your Black Ink - FOGRAxx grayscale into the K channel. That will be treated as a perfectly standard CMYK file, but as it happens with content only in the K channel.
By @D Fosse

If you want only the black channel of CMYK to have information, in the original grayscale image, you could Select All and Copy the Gray channel in the Channels panel. Then convert the grayscale image to CMYK. Target only the K channel and Paste. Then target the C, M, and Y channels one at a time and fill them with white.
By @barbara_a

This is a more complex procedure for me and I have lots of images, but thank you for the advice, it may come handy sometimes.

It sounds you are getting the results that you were hoping for with grayscale to cmyk conversion.
By @Chris 486

Most probably you are right. But I wanted to make sure that I'm doing everything right, to understand how this works and to clear up this confusion regarding the proof preview. Thanks.