Re: setting the color of cropmarks

[Henning Hraban Ramm <texml@fiee.net>]

> Am 2019-12-19 um 19:11 schrieb mf <massifr@fastwebnet.it>:
> 
>> There is no option to change the color for the rules and the only option you have is to use color conversion.
>> \setupcolors[cmyk=yes,rgb=no]
> I do have this setup, but it produces grayscale crop marks.
> 
> I was told by two different printshops that grayscale raises problems with recent versions of PDF software (verification? imposition? I've not asked), that complains about that, because it treats grayscale as RGB, splitting it on C, M and Y channels, instead of mapping it only to the K channel.

I’d regard that a misconfiguration on their side.

Maybe it helps to define the output intent:
https://wiki.contextgarden.net/Command/setupbackend
https://wiki.contextgarden.net/PDFX

>> If you need more control you can create your own marks and add them as background for the page.
> I've seen there's something about that in the mailing list history. I'll look into that.
> 
> BTW, the MP file producing the marks is
> 
> metapost/context/base/mpiv/mp-crop.mpiv

Sorry for mixing up marks and markings.

> Am 2019-12-19 um 19:08 schrieb Hans Hagen <j.hagen@xs4all.nl>:
> 
>>>> Can I change their color, in particular into a CMYK black (0,0,0,1.0)?
> 
> Just curious ... isn't gray (g G) equivalent enough? I assume that a cmyk prepress document can have gray scale images too.

Grayscale color space is device dependent, as well as CMYK and RGB color definitions without a profile; it should be the same as black CMYK channel, but needs not to.

>>> It would also make sense to use CMYK register color (1,1,1,1).
>> I do agree.
> I might agree if I know what is meant here.

Massi said the crop marks are defined in grayscale black, but wants CMYK black.
In layout programs crop and registration marks are usually set in a color named "Registration" (not register, my mistake) or the like, and it maps to all color plates, i.e. mostly CMYK 1,1,1,1, but also spot colors. You need that for manual film montage.

Greetlings, Hraban
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