[cairo] Spot colors (and CMYK)

[Chris Murphy]

On Feb 20, 2010, at 5:19 AM, ecir hana wrote:

> 
> Because of two things: making ICC profiles mandatory would make you
> unable to use spots you don't have profile for, such as Pantones. A
> spot is just a name which doesn't even need to have LAB alternative.

I do not follow the logic on this at all.

An XYZ or LAB alternative for a spot color is an obviously good idea if you want to see the spot color on any kind of device that does not print with the exact spot color (ink in a bucket). Depending on how the spot channel is used, determines how it would be defined.

If it's just for a logo or something like that, an ICC profile for the spot color isn't necessary, just an XYZ or LAB value so it can be displayed and proofed properly.

If it's used in a photographic image, for example, then yes an ICC profile would obviously be required. This same profile would have been used to convert the image from RGB to e.g. CMYKGO in the first place, then the six channel object is tagged with that profile so that, again, it can be displayed and proofed.

If you insist on untagged device values, you can only use spots except where ink in a bucket is present. Bad idea.


> Second, no matter where I print or what profile they use I want my
> text to be CMYK(0, 0, 0, 100).

Wrong. You want a particular result, and specifying it as 100K isn't going to get you there because some downline process *will* convert it the instance K100 isn't available. It's important to define the object type. Black text is unique and needs variable handling. Simply saying it's always 100% K can result in incorrect handling.


> That said, I understand that untagged CMYK is difficult to show on the
> screen. I'm not against tagged content - I'm against making tagging
> mandatory for spots. Perhaps always tagged CMYK is even a good thing
> but for DeviceN that means only its fallback. (And I could always
> create untagged DeviceN with cyan, magenta, yellow and black). I also
> believe DeviceN should have its fallback defined in CMYK only, and the
> fallback should compose over CMYK only, as well).

This makes zero sense to me.


Chris Murphy
Color Remedies (TM)
New York, NY
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Co-author "Real World Color Management, 2nd Ed"