Export RGB images/doc to CMYK pdf

[Meh12345678910]

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?

[Derek Cross]

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.

[Meh12345678910]

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? 

[Meh12345678910]

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. 

[rob day]

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?

[Totalle25947761hhx2]

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]

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.

[Totalle25947761hhx2]

The problem page is above in the first screenshot. You can see the difference in the blacks. It is subtle, but there. 

I've attached the separations preview (when in RGB blending). Again, it's telling me the output for both the background rectangle and the image will be the same (attached).

I've now switched RGB blending to CMYK as (I think) you are suggesting to correct any text over transparency issues. 

I could change all the background rectangles to CMYK values, but it would take months...

Separations output shot below. Same values on rectangles and images. 

[Totalle25947761hhx2]

Sorry - I've just realised that I'm signed into a different account. Meh and I are the same person!

[rob day]

Can you share the files?

[rob day]

You should be able to attach the InDesign page and placed image in a reply

[Willi Adelberger]

I recommend to use RGB images, but vectors in CMYK, without color profile to avoid a 4c conversion.

[Meh12345678910]

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]

Share the PDF you sent to the printer.

[Meh12345678910]

I'm really not comfortable with that! Ask me anything about the settings I'm using. But no way am I putting years of work (and 300mb) online...

[rob day]

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.

[Meh12345678910]

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]

You really have to use AcrobatPro to inspect a PDF—Photoshop or a generic PDF reader wouldn’t tell you much. You don’t need to share your entire document, just one of the pages that is outputting wrong. In AcrobatPro you can use Output Preview>Object Inspector to check the color space and profiles of objects on the page.

[Meh12345678910]

This is what AP shows me on the object info. The colour profiles are the same... but way more info on the image black vs the object fill black. Now.. show to make them the same? Could it be the 32bit -ness?

PS, couldn't find the print as image box on the pdf export dialogue... any hints on where to find it?

 

[rob day]

Let’s see the Separation view with only the Black plate visible:

[Meh12345678910]

 It says 90 all over the black area - both fill and image. But the top half is coming out greyer in print.

I tried another page where the grey was more pronounced, and it did show a difference there 88 vs 90, but why? There is no difference between the fill and the background black, and yet both are coming out as different shades. Even when both are 90...

[rob day]

Really can’t help without seeing a file sample. Is there a reason you are making a conversion into US Web Coated SWOP CMYK? I the printer an offset web press?

[Meh12345678910]

Thanks. I did actually try making a single page to share, but for some reason the file is still 149mb!

the printer asked for generic Cmyk so I chose that one. In the end I sent them an RGB file anyway and they accepted it, but clearly during their own conversion the same thing is happening. It's like Indeeign encodes line art/fills differently or compresses them in a different pattern. 

[rob day]

It's like Indeeign encodes line art/fills differently or compresses them in a different pattern.

Then that would show up in the PDF, and you are saying it doesn’t?

[Meh12345678910]

It doesn't necessarily show up in Acrobat, but it does in other readers and in the final print.