Grayscale conversion in Acrobat for printing (Black Plate)

[sd5e8a]

Hi,

If we have a PDF with color and grayscale images (for example: sRGB and sGray) and if it has to be converted for offset printing, some people suggest that the grayscales should use the CMYK black plate.

What's the correct way to do this in Acrobat?

a) Using Acrobat's Color Converter, that is: converting the grayscales to the required CMYK profile with "Preserve Black", "Promote Gray to CMYK Black" and "Preserve CMYK Primaries" checked?

b) Editing the images externaly in Photoshop one by one, that is: loading a custom gray in Color Settings (the Black ink of the required CMYK profile) and then converting to "Black Ink - the name of the required CMYK profile"?

c) Something else?

Thank you.

[ZBalling]

sRGB and Y only sRGB, somehow called sGray are not CMYK. They are RGB.

[sd5e8a]

Yes, I know, I'm asking what would be the recommended way of converting the sGray images in Acrobat to CMYK (Black Plate).

[JR Boulay]

A grayscale file is printed on the K plate in any case.

"that is: converting the grayscales to the required CMYK profile with "Preserve Black", "Promote Gray to CMYK Black" and "Preserve CMYK Primaries" checked?"

There is no "Black", no "Gray" and no "CMYK primaries" in a RGB file, so it does not matter.

You have to use Acrobat's Color Converter and select a grayscale profile, here we mostly use the "Dot Gain 15%" for printing but ideally you should use the profile requested by the printer.

[sd5e8a]

Thank you, @JR Boulay.

Just for clarification, the book that I'm working on should contain color and grayscale images.

From what I've read on this forum, I got the impression that all the images (RGB and sGray) should be converted to the same CMYK profile - the one required by the printer (let's call the profile "Uncoated FOGRA XY").

In this way:

- the RGB color images will be converted to CMYK color images ("Uncoated FOGRA XY")

- the sGray images will be converted to CMYK, but only the Black ink of "Uncoated FOGRA XY" will be used for them.

So, in Acrobat, I converted a test page with sGray images to "Uncoated FOGRA XY". But I got 4-color grays, which I don't want (I noticed that in Output Preview).

That's why I checked: "Preserve Black", "Promote Gray to CMYK Black" and "Preserve CMYK Primaries" and the problem was gone.

During the conversion, the appearance of the images changed (they brightened), but I thought that this is normal.

I thought that this is the correct way to do things.

Maybe I misunderstood something, I don't know.

[JR Boulay]

Yes, sorry. I made a mistake.

According to the doc:

Preserve Black: Preserves any black objects drawn in CMYK, RGB, or grayscale during conversion. This option prevents text in RGB black from being converted to rich black when converted to CMYK.

Promote Gray To CMYK Black: Converts device gray to CMYK.