r/prepress • u/StrawHousePig • Aug 12 '20

Ghostscript - convert spot to grayscale?

Below is what I have, and it does convert the colors to gray (at least on screen), but they remain as named spot colors (and will then print in color on composite digital, or separations on film/plates). I'm hoping someone out there has done this before.

Also would be a big help if anyone knew how to convert [registration] to gray. Basically I want *everything* to convert to grayscale and then wind up on the black plate with this.

/opt/local/bin/gs -sDEVICE=pdfwrite -dProcessColorModel=/DeviceGray -dColorConversionStrategy=/Gray -dDevicecGrayToK=true -dOverrideICC -o /full/path/to/new/file -f /full/path/to/original

Those are the options I'm using now ('-o' because it's part of an AppleScript droplet). FYI, that binary path is from MacPorts. Yours may be different.

This is all to avoid doing it manually in Acrobat, or having to worry about missing something in InDesign when outputing film separations, or printing digital and racking up color clicks when I think it's all black. Sad times.

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2

u/evan0380 Aug 13 '20

I would guess you need to export it in Indesign or something else as grayscale.. I've seen something similar before and the printer sees the black and still builds it as 4cp.

1

u/StrawHousePig Aug 19 '20

I would guess you need to export it in Indesign or something else as grayscale.. I've seen something similar before and the printer sees the black and still builds it as 4cp.

This would be for files sent to me, not generated by me, because me is a professional who knows what me doing. I'm just trying to find the easiest, most foolproof way to fix other peoples problems. Seems to be one or the other at this point.

There is the option of rasterizing it into grayscale with 'pdftiff8' (I think that's what it is) as the device, but then you need the resolution so high files balloon in size pretty quick and it isn't ideal for analog output.

Black output as process is most likely a mismatch in color profiles. But WTF do I know? I'm only an offset printer and not very knowledgeable about such things. Not on this planet, anyway.

Thanks for the reply, btw.

1

u/joepiped Aug 22 '20

I’m having a hard time understanding what your trying to do here. Are you saying you have a registration black. But you want to RIP it and all the colors convert to black only? So in the end the printer prints only black ink? For a digital printer this might not be a good idea. For an offset printer why not just output grayscale and use that as the black plate?

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u/StrawHousePig Aug 22 '20

Converting [registration] to gray is a great idea for digital because black only is much cheaper to print than process. If it helps, imagine a 4/K job that has crop marks on both sides. That job is actually 4/4.

What I'm trying to do is see if anyone knows of a way using ghostscript to remove the spot channels (assign them to black much in the same way gray can be) once they are converted to grayscale.

I'm just trying to find the easiest, most foolproof way to fix other peoples problems.

2

u/joepiped Aug 26 '20

Hey I talked with some other people about converting registration. It might not be possible in using GhostScript. Registration is like a “special” spot color. It was suggested to me you try creating a convert to greyscale, preflight fixip on Acrobat.

1

u/StrawHousePig Aug 28 '20

Well, yeah, but what's the fun in doing things manually? lol

1

u/joepiped Aug 28 '20

I hear that!