colors in pdf (acrobat reader) much darker than in indesign

[Cacadriil]

Hello,

When I generate print-ready pdf files in InDesign, and then look at the pdf using Adobe Reader, the dark regions of the photographs come out completely black.

I have opened the pdf in Adobe Reader, then saved a screen dump, and then opened the latter in Gimp, in order to check the exact RGB values in the dark region. Everywhere in the dark region, the colors are like #000001 or #010002 or similar. When doing the same with a screen dump of InDesign, I find values like #251B11.

As a result, in InDesign I still see lots of details in the dark regions, but in the pdf, I don't. In the picture as shown on screen in Adobe Reader, the information about the nuances and shades seems irretrievably lost.

Using ImageMagick's "identify" command, the source image is reported as

    JPEG 3881x2912 3881x2912+0+0 8-bit sRGB 1.09648MiB 0.047u 0:00.038

which specifies the original color space, sRGB.

Using "PDF Shaper" to extract the image from the pdf file, the resulting image identifies as:

    JPEG 2044x1534 2044x1534+0+0 8-bit CMYK 704048B 0.000u 0:00.001

which specifies some CMYK color space. Clearly, when displaying the page on a screen, Adobe Reader must convert the CMYK back to some RGB color space. In the resulting round trip conversion, almost all information is lost from the dark region.

I cannot tell to what extent the information is lost in the first or second conversion.

What can I do? Should I better have InDesign work entirely in the sRGB color space? Is this possible? If so, it would be left to the printer's software to do the required conversions to whatever color spaces his machinery does work in. Is there any point in having Indesign convert the pictures to CMYK?

Thanks

[bartbossuyt]

What are your color export settings when exporting to PDF from within inDesign?

[Cacadriil]

@bartbossuyt: The export dialog's section for printout (whatever it's called in English) says 

Color Conversion: Convert to target (Keep values)

Target: Document-CMYK-Coated FOGRA39 (ISO 12647-2:2004)

Policy for profile inclusion: Do not include profiles.

[rob day]

It’s because you converted everything to CMYK and did not include a profile. Acrobat Reader would need a profile or Output Intent to soft proof the CMYK color. If you save as PDF/X there will be an Output Intent Profile included for CMYK soft proofing, but you really want to use AcrobatPro for checking output.

Also, set your PageDisplay>Use Overprint Preview to Always., that will force a CMYK preview

[rob day · Accepted solution]

Export your PDF using PDF/X-4 preset, and evaluate the PDF using AcrobatPro with Output Preview turned on. AcobatPro’s Output Preview Separation values will give you accurate print output values—Reader does not have an Output Preview. A screen capture would give you monitor RGB values and not the actual print CMYK values.

[Cacadriil]

Thanks! That was very helpful. 

I just exported using the PDF/X-4 preset, and

   ... Wow!

So different! 
I did not have Acrobat DC Pro installed, so I just opened the new pdf in A.Reader. Wow. Even printing out from Reader gives a very satisfactory result. All details I expected to see in the dark region, were clearly visible. Previously, I must have made a very poor choice of Export settings.

Now I have installed DC Pro also, Print preview allows me to "switch off" each channel (C, M, Y or K) separately. Very instructive!

But I would like to access the numerical values used to represent the colors of the pixels, even if those numbers refer to channels in some particular CMYK color space. Is this possible?

The goal is to know to what extent the bad pdf's I created could be salvaged. For that, the different shades in the original need to be represented by different numbers in the bad pdf. As long as numbers are different, those differences can be magnified and become perceptible, although I suspect that I would see some "banding".

Thanks again.

[rob day]

But I would like to access the numerical values used to represent the colors of the pixels, even if those numbers refer to channels in some particular CMYK color space. Is this possible?

Just mouse over the preview image, and you will get the numbers for the Simulation Profile. When you export to PDF/X-4 the Simulation profile will automatically be set to the Output Intent profile and the separation numbers will be the document CMYK numbers—there’s no color conversion.

I doubt there is a problem with your previously exported PDFs. Just set the Simulation profile to the Fogra 39 profile you chose as the Destination profile, that should give you the same preview and output numbers from the InDesign file.