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Question

Export RGB images/doc to CMYK pdf

Forum|Forum|3 years ago
October 20, 2022
4 replies
1143 views

Complete beginner here. I have a book with thousands of RGB images on a black background, some of which sit in black rectangles as extensions of that background. The first printer I used wanted an RGB PDF (presumably they do CMYK conversion later), so that was easy enough to export under the interactive/web option.

However, the second printer wants a generic CMYK version. When I try to export (US Swop 2; convert to destination; preserve numbers), the black on the background of the images does not match the rectangles behind.

Tranparency blending is set to RGB. Black rectangles are RGB 0/0/0. Black backgrounds on images are also RGB 0/0/0. I've checked and double checked that. But in the CMYK PDF output, they are very subtly different. Is there a quick and easy way of rectifying this?

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Peter Spier

Community Expert

If the blacks are the same in the PDF, but print differently on press, the problem could well be the RIP handling raster and vector content differently.

M

Meh12345678910Author

Participating Frequently

Still haven't found a solution to this. For some reason it's exporting the background rectangles differently to the black in the images. I submitted an rgb file to the printer, and when I proofed it in the pdf reader, the blacks looked the same. But for some reason they've printed differently. I really don't know what's going wrong. Anyone?? Photo of printed page attached.

rob day

Community Expert

Share the PDF you sent to the printer.

M

Meh12345678910Author

Participating Frequently

I can’t replicate the problem so it is specific to your file, or the print settings.

Some composite RGB printers will color manage vector and raster images differently—checking Print as Image might help.

Okay will try that, thanks. One more interesting thing.

if I open a pdf page (exported as Cmyk) in Photoshop, it tells me the blacks are the same. If I open it in any pdf reader, you can see they are different. Why might this be?

rob day

Community Expert

I have a book with thousands of RGB images on a black background

Hi @Meh12345678910 , What format are the placed RGB images? JPEG compression could cause some variation in the black backgrounds.

If you set your Transparency Blend Space to RGB, Black only text you want to output as 0|0|0|100 CMYK black will convert to 4-color, which might be a problem on press. Are you using any Blending Mode effects with the image and/or ID backgrounds?

Do you get the mismatch if you turn on InDesign’s Separation Preview and check the output values? Also open the Color panel and confirm the RGB fill:

Can you share a sample page with placed images that are causing the problem?

T

Totalle25947761hhx2

Participant

Thank you.

Yes, all the text is in the correct type of black for printing; I was careful with that!

Have attached a pic of the output with issue and also checking with the dropper to make sure background fill and image match. Which they do...

Images are in sRGB 2.1 and so is the RGB workspace. I've tried playing with the appearance of black settings and the Separation panel as you suggest, but the difference in the blacks just isn't visible in Indesign.

rob day

Community Expert

also checking with the dropper to make sure background fill and image match. Which they do...

Don’t use the Eyedropper it doesn’t tell you anything about output. Check the output values with Separation Preview.

Yes, all the text is in the correct type of black for printing; I was careful with that!

But if the Blend Space is set to RGB and there are transparent objects on the spread, CMYK 0|0|0|100 black will not output as black only. You can see that here wher my blend space is RGB and there is transparency. The Color panel tells me the text is filled with [Black], but Separation Preview shows it as 4-color:

I think you have to share the problem page and placed image, otherwise we are only guessing.

Derek Cross

Community Expert

The recommended preset nowadays is normally PDF/X-4 and keeping your images in RGB color mode and usually as single pages (not spreads) ticking Crop Marks and Use Document Bleed Settings. But if your printer asks for another spec go for that.

M

Meh12345678910Author

Participating Frequently

Okay, and when I try to export my RGB images to CMYK, something is happening during conversion to make the two RGB blacks in the original document not match in the output PDF. What could be causing this?

M

Meh12345678910Author

Participating Frequently

Sorry, to clarify - I'm not converting the images in the original document. They're always RGB. I mean when I export the document to CMYK, the images in it are converting in unexpected ways.

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