How can I check/convert pdfs to ensure true grayscale when placing in InDesign

[Natalie Ruffing]

I'm using InD to design an Awards Program which will have a grayscale interior and color front and back covers, the final document will be exported in as a PDF in CMYK. The printer won't be receiving the cover in a file separate from the interior, the interior front and back covers are grayscale.  I'm receiving lots of ads to place in the program in the form of pdfs which have C,M,Y values and even RGB values. In earlier year's programs I've seen the grayscale ads appear with a color cast. I'd like some help understanding a couple things to ensure the Awards Program won't have any color casts. Here's what I'd like to understand:

If a pdf file has C,M,Y values will that cause a color cast? Is it only if the C,M,Y values are not all equal that a color cast if caused? Or is it only when the pdf contains RGB that a color cast is created?

When I find a pdf that has C,M,Y and/or RGB values I've been converting it in Adobe Acrobat using  Print Production -> Convert Colors and selecting one of the Dot Gain conversion profiles. My questions for this are:

1. Would this be better accomplished with another program, or is Adobe Acrobat the best? I've found trying to do it in PSD greatly increases the file size and rasterizes all the fonts ruining the quality and ability to edit copy later.

2. On pdfs where C,M,Y or RGB values are contained I've been using a variety of the Dot Gain profiles including Dot Gain 10% to get a richer black so the ad doesn't appear faded once it's in grayscale. I've heard the norm is Dot Gain 20%. Will using Dot Gain 10% cause any problem when the converted pdf is placed into InDesign and then exported as CMYK and sent to the printer?

Sorry for the lengthy post, thanks in advance for any help.

[Dov Isaacs · Accepted solution]

Yep, those ads produced in PowerPoint are really a pain in the tuchas! 

Let's assume for the time being that you have no issues with what you are natively producing in InDesign and that all your grays are tints of black, i.e., CMYK=(0,0,0,k) where k=1 for pure black. In this case, you shouldn't have any issues.

I assume that the problem is really with the placed ads. Some considerations:

(1)     If you have content with CMYK=(c,m,y,k) where c=m=y, you will still likely have some color cast and possible registration issues for small text sizes. You don't want this.

(2)     You don't want your final PDF file to have any ICC color managed grayscale since, depending upon the RIP/DFE/renderer, might yield some undesired rich black with the problems noted in (1) above. Only DeviceGray yields K-only black, G=g => CMYK=(0,0,0,1-g). If you do convert to grayscale with a dot gain profile, use a Preflight profile or Acrobat's Convert Colors functionality to “decalibrate” the resultant grayscale (i.e., keeping the same gray value, but removing the ICC profile).

(3)     You absolutely should not open PDF files in Photoshop to “fix them” in any way.

(4)     You should specify that your advertisers either provide a PDF/X-4 file (for you to place in InDesign) or provide the source file for you to create the PDF yourself; this is especially important for content produced from Microsoft Office applications (such as PowerPoint-created ads). For such Office files, you should open them with the Windows version of Office and use Acrobat's PDFMaker capability using either the High Quality Print preset or, if you have the latest version of Acrobat Pro DC installed, the new Standard profile. This would ensure that any R=G=B text or vector in the Office document exports as grayscale!

Good luck. Having spent many “volunteer” hours putting together programs for various non-profits / charities, I know that this is very time-consuming and frustrating work!

          - Dov

[Natalie Ruffing]

Dov, thank you! I think you have clarified something that used to cause me endless headaches. Just to ensure I'm interpreting correctly when I work within Acrobat Pro to convert a pdf with C,M,Y and RBG values to grayscale the best option is preflight.

Preflight > Digital printing (B/W) so that it converts everything into process black.

But I can also go through Convert Colors twice:

First to choose a Dot Gain profile.

Second to decalibrate removing any ICC profile.

However, while this works it probably isn't ideal as the grayscale seems to lack a lot of contrast (black doesn't get rich). 

THANK YOU!

[rob day]

However, while this works it probably isn't ideal as the grayscale seems to lack a lot of contrast (black doesn't get rich).

The conversion you are showing in your #2 is showing the starting source profile as US SWOP Coated. In a SWOP to Grayscale conversion black only CMYK (0|0|0|100) wouldn't convert to 100% gray which would explain the loss of contrast—0|0|0|100 would convert to something like 90% gray.

Another way to do this is from InDesign exporting the pages you want to be grayscale to a gray profile, and then combining the color and gray pages in AcrobatPro.

Set your Appearance of Black Exporting Preference to Output All Blacks as Rich Black. This will prevent the 0|0|0|100 CMYK to 90% gray conversion:

Export to PDF/X-4 with the Output Destination set to 20% Dot Gain:

With the PDF/X-4 preset objects converted to the Destination profile do not include a profile—DeviceGray in this case

[rob day]

I've been using a variety of the Dot Gain profiles including Dot Gain 10% to get a richer black so the ad doesn't appear faded once it's in grayscale. I've heard the norm is Dot Gain 20%. Will using Dot Gain 10% cause any problem when the converted pdf is placed into InDesign and then exported as CMYK and sent to the printer?

The Dot Gain 10% profile wouldn't have any affect on the richness of a grayscale's 100% black.

If you are working in grayscale mode the assigned profile affects the preview and not the output values. The grayscale preview would be adjusted the most in the midtones with a curve based dot gain profile.

These two grayscales have identical output values. The version with the 10% Dot Gain assignment tries to preview what will happen if the press has a uniform 10% dot gain, but if the press is actually running at 25% dot gain the darker bottom version will be a more accurate preview.

The flip side is if you are making a color conversion i.e. RGB-to-Grayscale, the destination grayscale profile affects the converted numbers—128|128|128 RGB gray converted to 10% Dot Gain would result in a higher grayscale output value than if you used 25% Dot Gain as the destination.

I’m guessing if you use 10% Dot Gain for a US sheetfed press, the middle and 3/4 tone output will be darker than you expect.

[Jeffrey_Smith]

My suggestion is to convert all interior page content to black/grayscale/one color.

And in Acrobat, I would suggest using the Preflight Tool > SIngle Fixups (wrench icon) > Convert color to B/W instead of the Convert Colors Tool. If you need all colors converted to grayscale, the Convert Colors Tool can miss some objects, leaving them unconverted.

[Gusgsm]

If the inside is grayscale to be sent in just one PDF exported from InDesign, the simplest way, in my opinion, would be exporting the PDF to PDF using the high quality preset and using the option "Convert to destination" in the "Output" Tab, choosing an ICC grayscale profile and making sure that you choose "Don’t Include Profiles" in the Profile Inclusion Policy. Everything will be Devicegray, I believe.

The point of avoiding the PDF/X standards is that you might be able to avoid including the ICC grayscale profile, as Dov Isaacs recommends.

If you just want to reprocess one or two PDF ads, you can refry them just by placing them in a new InDesign file and using that method.

Bye

[rob day]

The point of avoiding the PDF/X standards is that you might be able to avoid including the ICC grayscale profile, as Dov Isaacs recommends.

It’s understandable that one would assume all objects export with an icc color profile with the PDF/X-4 standard—in the Output tab for default PDF/X4, the grayed out Inclusion Policy shows Include All Profiles, or Include Destination Profile if a CMYK or Gray Destination is chosen.

But, if you check an exported X4 with AcrobatPro's Object Inspector, you'll see that all objects converted to a chosen Destination space are listed as DeviceCMYK or DeviceGray (see the last capture in my #5).

If you export with the default X4 preset (No Color Conversion), only objects with color profiles that conflict with the document‘s assigned CMYK profile export with a profile. All Document CMYK color (native colors and place objects with the same CMYK profile) exports as DeviceCMYK (no profile). A PDF/X does include an output intent profile, but that's not the same as an embedded profile.

[Gusgsm]

But, if you check an exported X4 with AcrobatPro's Object Inspector, you'll see that all objects converted to a chosen Destination space are listed as DeviceCMYK or DeviceGray (see the last capture in my #5).

Yes, but lacking output intent deletes all reference to an ICC profile. Just in case