PDF Photo book of black and white images

[Amado5FAB]

Hi Everyone,   I'm creating a photo book of black and white images which were taken from an iPhone and edited using Snapseed. I initially had some issues resizing the images to 300 DPI using an online site due to a green tint or hue on my images. I thought I could work with Indesign alone without having to use Photoshop. I then decided to use Photoshop to resize the images to 300 DPI and converted them to grayscale. The PDF actually contains a spread with colored fonts which I may delete if it becomes too much trouble for me to consider. My question being are there any settings that I should be aware of to export the PDF in grayscale? Thanks 

[Steve Werner]

This article I wrote might help you. The title says its for InDesign CS6 but it works the same with a current version of InDesign:

https://creativepro.com/finding-export-pdf-to-grayscale-in-indesign-cs6/

[Amado5FAB]

Hi Steve,   Thanks for responding to my message. I was just wondering what is the difference with all the dot grains from 30 / 25 / 20 / 15 and 10. Also, I did mention that I had a page spread which contained colored fonts. Would the grayscale conversion remove the colors?

[Derek Cross]

It's "dot gain" and this Wikipedia description will tell you more about it than you'll want to know!  https://en.m.wikipedia.org/wiki/Dot_gain

[Amado5FAB]

Hi Derek,   So if I understood the Wikipedia article, ideally you would want the dot gain to be 10 to make the print as close as possible to the PDF. ( the previous post mentioned a dot gain of 15 ). I've also seen it mentioned somewhere that one has to account for the light source in a computer screen which makes the images much brighter than the actual print. 

[rob day]

How is the book being printed? If it’s offset printing does the printer tell you what CMYK profile to use?

[rob day]

If your document has a mix of color and grayscale you cannot export it to a grayscale PDF—the color will get converted.

When you place a grayscale in InDesign it gets displayed on the CMYK black plate. Its preview is generated by your document’s CMYK profile assignment, which needs be the profile for the press the book will be printed on.

By default Photshop uses the 20% Dot Gain Gray profile for a grayscale’s preview—InDesign does not have a Grayscale space so you can’t use grayscale Dot gain profiles. Photoshop has the option to use Black Ink profiles, which can be generated from any CMYK profile. Ideally you should be using a Black Ink profile that matches the CMYK profile you are using in InDesign. This thread has instructions on creating a Black Ink profile in Photoshop:

https://community.adobe.com/t5/indesign/dot-gain-or-gray-gamma/td-p/8365606?page=1

[Amado5FAB]

Hi,  I forgot to mention that the photo book will be on offset print. But, I'm a little confused. Was I wrong in converting my images to grayscale in photoshop? 

I also just got in touch with the printer re: settings for dot gain. I will find out soon. Thanks everyone for responding. I am learning new things as we go through this process. I'll be back as soon as I hear back from the printer. 

Amado

[rob day]

Was I wrong in converting my images to grayscale in photoshop? 

Not if you want the images to print with only black ink.

Leaving the black and white images as RGB would convert the gray values to 4-color CMYK. That can result in images with more dynamic range, but it can be hard to prevent color casts if the press gray balance is a bit off (the green tint you mentioned in the original post).

Rather than dot gain you really want to know what the press CMYK profile is and assign it to your document—modern CMYK profiles handle all of the press properties like dot gain, paper stock, ink colors, black generation etc. If you use one of the legacy dot gain curve profiles in Photoshop the image preview will likely change when you place the grayscale in InDesign because InDesign uses the CMYK profile’s black ink for the preview and not the placed grayscale’s profile. Here’s the difference you would see placing a 10% Dot Gain grayscale in InDesign with the default US Web Coated SWOP profile assigned:

[Amado5FAB]

Hi Rob,

The images are not sepia or duotone. So, yes I do think using photoshop to convert to grayscale is fine. However,  why do we have to export PDF Indesign in grayscale when images were already converted to grayscale in photoshop? Shouldn't Indesign recognize the grayscale images?

With re: leaving the black and white images in RGB. I initially had the images in RGB but was told to convert them to grayscale since they would be using black ink and not the color press. I am a bit apprehensive since I do want the dynamic range.

 I am still waiting on the reply from printer which may not be until next week since I was told that the print would be done in China. 

[rob day]

However,  why do we have to export PDF Indesign in grayscale when images were already converted to grayscale in photoshop?

You don’t, just export to a regular press PDF preset PDF/X is the best and the grayscales will export unchanged—the gray values will be on the black plate in the PDF when you export with Document CMYK as the Destination or No Color Conversion.

[rob day]

Shouldn't Indesign recognize the grayscale images?

You can check what inDesign does with a placed grayscale via the Separation Preview panel. Here my document has the default US Web Coated SWOP CMYK profile assigned, and I’ve placed a grayscale with the Black Ink version of SWOP assigned:

If I hide the Black channel you can see the grayscale will output to black only:

Exported via the default PDF/X-4 preset, AcrobatPro‘s Output Preview shows the grayscale is unchanged in the PDF:

CMY hidden