Multichannel from RGB?

AA
Posted By
Aaron_Andrade
Mar 5, 2004
Views
269
Replies
3
Status
Closed
I am working on a 2-color job (PMS 187C and black) in Photoshop 7 and InDesign CS (Panther). Client has provided RGB JPEGs of some posters that they want included in the layout. These posters use red strongly and symbolically. An example at:
< http://www.who.int/entity/violence_injury_prevention/violenc e/global_campaign/en/PostRedGeneral.pdf>

How do I repurpose these JPEGs using the 2 inks at my disposal, while retaining some of the contrast between (using the example of the link above) the red hand and the other hand?
Duotone is too uniform. I expect the solution involves Multichannel mode and some tweaking — but i’m not sure of the best approach.

Thanks in advance.
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david_marley
Mar 5, 2004
Try this:

1. Convert the RGB with Image>Mode>Multichannel. This will rename the channels as cyan, magenta, and yellow.

2. Delete the yellow channel in the Channels palette.

3. Double-click the cyan channel in the Channels palette (to the right of the color name). After the channel options dialog opens, click on the color swatch and change the color to 0c0m0y100k. Also, rename the swatch to Black.

4. Repeat step 3 with the magenta channel, but after clicking the color swatch, select the custom color dialog where you can assign PMS 187.

5. Make a selection of the lighter hand and reduce the red component of this part of the image. Also, tweak the black to taste.

6. Save as a Photoshop DCS 2.0 file. Be sure the spot color check box is selected. To improve compatibility with printers and output devices, you can add empty (all white) cyan, magenta and yellow channels before saving.

Hope this helps.
AA
Aaron_Andrade
Mar 5, 2004
David,

I do believe that will work! Brilliant. Thank you.

Just one thing: any risk in losing data from the yellow channel when you delete it? Is there a way to merge it with magenta to retain some info?

Thanks again.
JS
John_Slate
Mar 5, 2004
Don’t worry about the yellow, delete away.

It’s probably quite similar to the Mag, and merging it in will make the red too heavy.

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