Preparing Old Photos in Grayscale for Offset Printing

I am preparing a history book filled with many old photos.

Will you be using InDesign to layout the book?

InDesign ignores Gray profiles and color manages placed grayscales' appearance via the document's CMYK profile. So if you color correct using the default 20% Dot Gain gray profile in Photoshop, expect a preview change when you place in InDesign.

In Photoshop you can use any CMYK profile's black channel as the gray profile and get appearance matches between Photoshop and InDesign with Overprint Preview turned on.

If you know the layout's expected CMYK destination you can use it as the gray profile—this would match InDesign's default US SWOP Coated:

Here are two InDesign grayscale threads that might help:

https://forums.adobe.com/message/4482662#4482662#4482662

Re: Grayscale images showing up too dark

The key phrase in your post is “a history book."

That leads to the following questions:

1. As a history book, is it fair to assume the book will be printed on an uncoated stock?

2. Will the images be incorporated with the text or as separate inserted signatures, allowing for a different choice stock surface for the photographs?

3. Can the production budget afford single color printing? double-black or duotone? four-color-black reproduction?

Specific file preparation instructions, guided by your answers to the above questions, may be provided by the printing firm. 

If this is for offset print, you need to decide (or find out) if it's going to be printed in 4 color, or on the black plate only.

• 4C gives deeper blacks and better contrast, and also allows slight toning, sepia or otherwise. For this you need to prepare the files as Adobe RGB or sRGB.
• K only is cheaper and for this reason often used. But it's very difficult to get a good contrast, because the black level is very high. It's more charcoal than black. The result tends to look muddy and with poor definition.

There's an additional problem with K only. Grayscale support is very poor overall, and any embedded grayscale profile may as well be ignored as not. As a result, you frequently get tonal changes.

One way around this is to get the CMYK profile that will be used, and put image content in the K channel only. Leave C, M and Y empty. This will preview correctly in Photoshop.

You can set up this as working gray. Go into working gray and click "load gray", and navigate to the CMYK profile.

Simple answer: Color management. You need to instate at least some basic form of it for consistent results.

Mylenium