Converting Images to Grayscale for Print

[michaelsgoldman]

Sorry, need help ASAP. I designed a book with 20 digital pencil illustrations. I have a hardware calibrated BenQ monitor. Sheridan (the Printer) specifies that for black only printing, all images should be converted to grayscale. Makes sense. They also specify the expected Dot Gain for uncoated stock on a Web Press is 25-27%. Ok cool. However, when I ask about grayscale profiles for 1) converting images to grayscale and 2) soft proofing the images on screen, they just keep answering that no profiles are needed for grayscale. To my knowledge, you cannot convert an image or even view an image without a profile. If a custom one is not selected, Photoshop will use the default profile. Which in my case is Dot Gain 20%. I don't know if I'm thinking about it all wrong, but here are my questions. PS, if you didn't guess yet, I have never printed a book interior in single color black only:

1. What is the best way to convert sRGB illustrations to grayscale for offset web press printing on uncoated stock? I want to prevent the images from darkening too much and losing the fine tone/texture detail in my digital pencil drawings.
2. I tried converting with Dot Gain 20%. It makes the images appear lighter on screen. I tried Dot Gain 25% and it make the images appear darker on screen than the 20% profile. Shouldn't the 25% profile appear lighter on screen than the 20% profile because it is compensating for more dot gain? The on screen effect is the opposite of what I expected.
3. Are Dot Gain profiles even still used in a modern printing workflow? I read on a post here that using just the K channel in CMYK is better for modern workflows.
4. For cover printing, when I asked about color printer profiles Sheridan recommended Coated FOGRA 39. On one of their documents they recommend GRACoL2006_Coated1v2.icc. And on another document for exporting to PDF they recommend U.S. WEB COAT (SWOP) v.2 if the document is not already setup for the correct color space. Are they trying to be confusing or are these profile so similar that it wouldn't matter a whole lot?
5. In the end, I just need to know how to ensure that my illustrations will print nicely on uncoated paper. How can I do this. Is it possible to soft proof for this on screen.

[michaelsgoldman]

Also forgot to mention that I am editing the images in Photoshop. Book layout is in InDesign.

[D Fosse · Accepted solution]

Open Color Settings, and in the Working Gray rolldown, click Load Gray and navigate to the CMYK profile that will be used for print:

If you start with an RGB file, converting to grayscale will now convert to the K component in the CMYK profile, which is what you want. It will also appear as a Convert to Profile option if you have grayscale files in other gray spaces.

InDesign does not have proper grayscale color management support. A grayscale file will just be sent directly and unmanaged to the K channel in CMYK and output on the black plate.

So this is the way to get the correct result. Effectively, since InDesign does not color manage grayscale, you're doing it in Photoshop prior to sending it to InDesign.

[michaelsgoldman]

Loading a CMYK profile as the gray space is a great tip. Didn't know you could do that.

I keep asking for a profile though and they have said multiple times that no profile is neede for grayscale. For the cover they mentioned the two in my original post (Fogra 39 and Gracol 2006). Then they have a document that says to output from InDesing to U.S. WEB COAT (SWOP) v.2 if the document is not already setup for the correct color space. But that is for coated paper.

How do I account for Dot Gain if they won't provide a profile for uncoated paper? Also, I would really like to know why the Dot Gain 20% profile looks lighter on screen than the Dot Gain 25% profile.

Thanks!

[D Fosse · Accepted solution]

Dot gain (ink spread in the paper) is built into all CMYK profiles. The dot gain profiles are outdated and not really used anymore. They're not accurate and don't correspond to modern printing processes.

But you need to know which CMYK profile. Keep nagging! You do need it for grayscale, as per above.

[michaelsgoldman]

Awesome, I will thanks! If I convert the illustrations to grayscale with a CMYK profile in Photoshop, and then place those illustraitons into InDesign, technically the file would already be in the correct color space and I would not need to convert on export again from InDesign? ie I could select "No Color Conversion" in InDesign?

And I'm still just curious. I don't understand why the Dot Gain 20% profile would display lighter on screen than the 25% profile. Isn't is supposed to be the opposite?

[D Fosse]

It depends on what else is in the ID file. There may be other RGB images that need to be converted to press CMYK. That does no harm, your grayscale images already are in that color space, so nothing happens to them.

How grayscale displays depends on whether the application supports grayscale color management. Photoshop does, so any grayscale profile will display correctly (and thus identically) as long as there is an embedded grayscale profile. The different tone curves are remapped into the monitor profile's tone curve.

But InDesign does not have grayscale color management. Any grayscale image will be interpreted as the K component in the ID working CMYK. And if it already is, that displays and prints correctly.

[michaelsgoldman]

You've been super helpful. Thank you so much! That all is making a lot of sense.

Since it seems important to included color profiles when moving files between applications and hardware, why would the printer specify that if the document is in the correct color space already to select "No Color Conversion" and "Don't Include Profiles" from the InDesign export settings?

[michaelsgoldman]

[D Fosse]

What I've always been told is that some RIPs - that's what produces the halftone screen - don't work well with profiles. I suspect that's older processes and it's not a real problem anymore, but I don't know.

It doesn't really matter in practice. A press-ready PDF will already be converted into final press CMYK, so the profile is redundant at this point and is not needed. No further conversions will be done.

[michaelsgoldman]

Ahh, I see. Then here's my final question:

If the printers prepress team is viewing different files on their monitors, converted to different profiles based on the clients paper specs etc, wouldn't they need the profile to view it accurately? Or perhaps they don't care how it looks on their screen, and they just assume that the client chose all the right settings for whatever printing equipment it's set to run on?

[D Fosse]

This is where the profile needs to be embedded. Then standard display color management applies: the document profile is converted into each system's custom monitor profile. Those corrected numbers are sent to screen, again representing the file correctly. If all these operators have properly profiled monitors, they will all see the same thing.

[Stephen Marsh]

Also, I would really like to know why the Dot Gain 20% profile looks lighter on screen than the Dot Gain 25% profile.

Thanks!

By @michaelsgoldman

Looks lighter where?

Photoshop or InDesign? And with what exact colour settings?