Have you used InDesign's Separation Preview and Acrobat's Output Preview to make sure the grey values are the same?
If you're going to speak to the printer, the best question would be whether or not they have an appropriate ICC profile or dot gain setting for you to use that represents what comes off their press, and use those settings in your Adobe Software.
Using 'Europe Prepess 3', there is a difference between how Photoshop and InDesign display greyscales. Photoshop would be using the 'Dot Gain 15%' greyscale profile, while Indesign would be using the black ink measurements of the 'FOGRA 39' CMYK profile. I tend to set Photoshop up to do the same, using 'Load Grey' and selecting the FOGRA 39 profile. But Acrobat, I've kinda given up with, as far as on-screen representation is concerned. By the time I'm looking at a press-ready PDF, all the colour decisions have been made, so it's not a big issue.
Assign all your CMYK or greyscale files, with the appropriate profile and when you export to PDF you select either 'No Conversion' or 'Convert to Destination (Preserve Numbers)' in the colour pane.
Do some printers process the pdf in such a way as to adjust for dot gain, so that, in effect, what gets printed matches the pdf (no allowance for dot gain) rather than the InDesign (which has added in the dot gain)?
Most printers do apply 'press curves' - adjustments done in the RIP to produce plates that help the press match certain standards, but those standards do have dot gain. So, if the press naturally runs at 20% dot gain, but the ISO standard specifies 15%, they'll knock the midtones back 5%. What you describe - applying press curves to achieve 0% dot gain, isn't very common, and any printer doing that would have to either make their customer aware of this and supply appropriate profiles, make adjustments to incoming files, or pay for a lot of customer rejections.
Thanks for your help and interesting points. To take them in order:
I hadn't thought to check the grey values as you suggest but have done so and they are the same. But, interestingly, when I view the black for the separations preview in InDesign, the photo suddenly now resembles the lighter grey I get in the Acrobat file. The photo is not colour - converted to greyscale in Photoshop and it says greyscale in the 'links' information in InDesign.
I do have the ICC profile from the printer - that is the Europe Prepress 3.
You say you've 'kinda given up' on the Acrobat on-screen representation but I'm reluctant to do so because it's much nearer what I got in print than the InDesign - though see the point above about when I see the black only.
Finally, if I do 'No Conversion' on the pdf export, I get a darker-looking on-screen pdf output - it much more closely looks like it does in InDesign on screen. But the colour conversion options are presumably part of the industry standard 'Press Quality' output that the printer wants, and I'm a bit reluctant to fiddle. At the moment that though seems the best way forward. I think I need a better technical grasp of what's going on and what the differences are but if there is a straightforward explanation I'd love to hear it!
Viewing the same images in Photoshop is much nearer to the InDesign, but perhaps fractionally lighter. I presumed this was all to do with dot gain and InDesign adding it in for viewing, but then Acrobat not making allowance for it (which would make sense).
InDesign doesn't have a grayscale color space and ignores embedded gray profiles. It also color manages the preview of grayscales in two different ways—with Overprint or Separation preview turned on you get a print preview showing how the grayscale will print on the CMYK black plate. In that case the preview depends on the document's CMYK profile—a 50% grayscale value will preview the same as 0|0|0|50 CMYK, which is what will happen on press.
With Overprint turned off you get an sGray (2.2 Gamma) preview and the CMYK profile has no affect, this is useful if you are designing for web or screens. If there is transparency on the page the blend space needs to be RGB in order to get the sGray preview.
When you export to PDF, placed grayscales will be DeviceGray (no embedded profile)—Acrobat's simulation profile is used to preview grayscale objects. So if you export to the default PDF/X-4 preset the Output Preview's Simulation Profile will match your document's CMYK profile and the previews (with OP turned on) will match.
You can also assign a Black Ink profile to grayscales in Photoshop (i.e., Black Ink - Coated Fogra 39) so that the profiling is consistent in all 3 apps. See these threads:
Thanks Rob. Sorry to be dim, but I think I am getting there. In really, really simple terms is the following about right?
InDesign is initially not assigning any profiles because it's greyscale anyway. But if I look at the separations preview, it switches on the profile, as it does when it exports to the (press) pdf. But if I select 'no conversion' on the pdf export, then the resulting pdf is a better match for I see 'normally' (no separations preview) in InDesign.
If that's more or less it, is it 'safe' to routinely select 'no conversion' so that what I get back from the printer will more closely match what I see in InDesign and Photoshop?
But if I select 'no conversion' on the pdf export, then the resulting pdf is a better match for I see 'normally' (no separations preview) in InDesign.
The only case where the grayscale exported values will change is if you force a conversion to a profile that's different than your Document CMYK profile (the profile assigned to your document) and in that case the grayscale will be converted into a 4-color CMYK object. So Convert to Destination with Document CMYK as the Destination will also export grayscales unchanged.
To get a color manged preview in AcrobatPro, you should open Output Preview and set the Simulation profile to match your InDesign CMYK profile or Coated Fogra 39 for the Europe General Purpose 3 preset you are using.
So here my Photoshop grayscale is assigned Black Ink - Coated Fogra39, the ID doc is assigned Coated Fogra 39 with Overprint on, and the Acrobat Simulation profile is set to Coated Fogra39. All three grayscales have the same values and their previews match.
This shows the sGray grayscale preview when you turn off Overprint/Sep Preview—if you are designing for screens and not print.
Note here I have Overprint turned off in ID, sGray is assigned in PS, and the simulation is to Gamma2.2 in Acrobat. All the previews are to the darker 2.2 gamma, but the output values haven't changed in any of the apps:
I'm not sure the greyscale exported values change, but the look of the images on the screen do change. Below left is the press pdf produced with 'no conversion' and below right with the standard 'convert to destination'.
The one on the right is what I sent to the printer and more or less what I got back print on paper. The point made about 'overprint preview' is interesting, and if I select that in InDesign then what I see is much closer again to the one on the right.
The long and the short of it is perhaps that, for a print project, it's worth switching on 'overprint preview' to see a better representation of what you are going to get in the pdf and back from the printer?
Below left is the press pdf produced with 'no conversion' and below right with the standard 'convert to destination'.
Are you viewing the two versions with the same Output Preview settings in AcrobatPro? The preview difference probably has more to do with the Profile Inclusion Policy than the Color Conversion setting.
Open both, and with Tools>Print Production>Output preview open, set the Simulation profile to your document's Coated Fogra39 profile. In that case you should get a match. The Preview Separations readout will give you the gray output values in the Process Black channel.
Okay, that's interesting. If I open the Output Preview in both Acrobat files, they both say Fogra39, but when I open that preview, the image on the left immediately and automatically lightens to match the one on the right! The one on the right stays the same.
Is it the case that I'm simply best off using InDesign's Overprint Preview to get a reasonable representation on screen of what I'm likely to get in both Acrobat (for press) and in print?
If I open the Output Preview in both Acrobat files, they both say Fogra39, but when I open that preview, the image on the left immediately and automatically lightens to match the one on the right! The one on the right stays the same.
Right, that's expected behavior and shows you that the output values are the same for both exports.
Turning off Overprint preview in ID gives you an sGray or sRGB preview of the gray values—you need to turn on Overprint Preview to get a color managed soft proof, which is dependent on the document's assigned CMYK profile.
That's really helpful and your time and knowledge much appreciated. I had thought Overprint Preview in InDesign was really just for colour work.