On Monday 06 November 2006 09:32 pm, Chris Mohler wrote:
> On 11/6/06, graffoo <[EMAIL PROTECTED]> wrote:
> > Look for the Decompose plugin - Colors>Components>Decompose...
> > CMYK - you'll get an image with 4 black and white layers. Then
> > you can save each layer as separate files you can use for silk
> > screen. To make shadings with dots, use Filter>Distorts>Newsprint
> > and play with the settings ;)
> Is it my imagaination, or are the CMYK layers inverted?
Yes, for printing purposes they are inverted after the "decompose" 

The amount of ink is marked in each pixel from 0 to 255 - so, if an 
image has some pixels with "zero yellow" (for example, white pixels) 
- the output of the decompose plug-in has this as "zero yellow ink"- 
meaning black. if it where full yellow, it would be full intensity - 
showing White.

In pratice, you  just have to invert that.

You can't however expect color accuracy with that plug-in. That is - 
you will have variations on the color you see on the screen and the 
color you get if you use the decompose plug-in, invert each resulting 
image, print that as a screen, and recompose the colors.

you may also want to increase the pixel quantity in your image, before 
using the newsprint plug-in.  Your target printing process have an 
ideal "lpi" number - arrange your work so that you have these lpi in 
the final image for each color.

Another way of doing this work you might find usefull is using the 
GIMP channels instead of layers for compositing your final image.

Just create a channel for each ink color you intend to use, and later 
apply the newspirint plug-in ont these channels.

As for separating, let's say, "dark blue" in a separate channel from a 
normal RGB image, I can think of the following procedure, which would 
have to be written as  a plug-in:

duplicate image, flatten-image, duplicate layer, color to alpha(remove 
desired channel color, on the underlying layer), set upper layer to 
'difference' combine mode, copy visible, paste as new layer, 
dessaturate, copy, create new channel, paste on new channel.

Perceive taht whatever you do, the "dessaturate" step will modify the 
finalc composition of your image you should spend some trial and 
error either in that step, or modifying the curve of the final 

Either way, I'd like to hear how you are doing when using GIMP this 


> I'm using GIMP version 2.2.13
> Chris
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