Replace a channel

janbak

Hi everybody,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
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this is my first post on this beautiful forum I've recently discovered ... I hope it's the first of a very long series <o:p></o:p>
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My question is: how can I replace a channel using all 10 channels available in different color methods? For example, what I have to do if I want to replace the Red channel with the Cyan one?

And ... how can I use blending mode to be sure to apply the change only in certain area of the channel I want to replace?
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Thx <o:p></o:p>

BinaryFx

Hi Janback, this sounds like a question for the Dan Margulis Applied Color Theory email list!

It would not be so common to replace the red with the cyan, replacing the cyan with the red would probably be more "common"...which is to say not very common for many people! Red and Cyan channels are related, as are GM and BY - however due to the nature of CMYK ink limits and dot gain, the CMY channels are generally less useful for blending than their RGB relatives (there are of course exceptions). The black and the Lab mode colour channels are sufficiently different that they do make much better blending sources.

Anyway, to broadly answer your question, there are many ways to replace a channel, however the best method is probably with the Apply Image command, which does not use the clipboard and one can use blending modes. Simply target the destination channel and apply the source document channel (both docs must be the same size). Usually normal, lighten and darken modes would be used for such channel blending (while overlay and the other "light" contrast modes for AB channels from Lab). This is often done in a duped layer, with the duped layer set to a blending mode such as luminosity mode, although it depends on the goal of the blend.


A related topic can be found at my website:

http://members.ozemail.com.au/~binaryfx/howto_mask10.html


Sincerely,

Stephen Marsh

http://members.ozemail.com.au/~binaryfx
http://prepression.blogspot.com