Getting colours from the channel mixer

DW
Posted By
Dave_Woodward
Jul 10, 2004
Views
1532
Replies
5
Status
Closed
Hi folks,

I am trying to use the channel mixer to changes areas of an image from green to another specififc colour, in one case yellow, in another red.

Trouble is, there are nine variables to play with and I am geting confused as to how to manipulate them to get a desired result.

I am happy to do some reading if you can point me to an article on the subject, if not, any help at all would be most gratefully accepted.

Cheers

Dave
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channel color mixer

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DM
dave_milbut
Jul 10, 2004
you might be better off using a hue saturation adjustment layer.
GD
glen_deman
Jul 10, 2004
I find the channel mixer very confusing as well! I’ve pretty much been able to avoid using it, since PS has so many other tools that can do any given job.

Dave’s hue/sat adjustment layer is a good idea; here’s what I did for a sample pic –

Make a mask that isolates the green portion of the picture (using select->color range, saving the selection into an alpha channel, using levels to increase contrast and finally tweaking with the brush).

For turning green to red, I first added a hue/sat adjustment layer, with the colorize box checked, and the hue slider all the way to the left. I also took down the saturation a bit and upped the lightness. I set the opacity of this layer to 90%.

Then I added a color balance adjustment layer on top. In each of the areas (shadow, midtones, highlights) I added a lot of red, added some magenta (taking out the green really), and added a little yellow. I set the opacity of this layer to 35%.

Finally I added a curves adjustment layer on top of it all and tweaked it some more. I set the opacity of this layer to 30%.

I really just sort of poked around; I don’t know a lot about color theory and such; in fact, you might even be able to do all of this with one curves layer, but this approach works okay. I find that the combination of adjustment layers is able to tackle the different needs of the color change (one layer gets it in the right color ballpark, the next layer pops the appropriate highlights, the next layer reduces the saturation so it doesn’t look too fake).

Here’s what the color changes look like: Crazy Bushes <http://www.geocities.com/bmphan/colorize.htm>
DM
dave_milbut
Jul 10, 2004
the channel mixer is ok for what it does. one thing i use it for is cleaning up channels… say you have near garbage in one channel (say blue) you can use the channel mixer to remove/replace much of the damaged data with good data from the other 2 channels.

but it can also be used to change colors (i just prefer to use hue sat for that)… to solve the op’s prob with the channel mixer, i’d open the mixer, select the red channel and crank up the red green and blue to 200, select the green channel and crank up the green. of course "yellow" is subjective (as is "green" we have no idea what color he actually started with. I chose a pretty bright green to play with). play with it to get what you want.
JS
John_Slate
Jul 11, 2004
Channel mixer basically alters the channel in the "Output Channel" field using percentages of the 3 other channels in the "Source Channels" section, adding to the channel on the plus side and subtracting from the channel on the negative side.

Beside creating drawing in an unwanted color (in CMYK mode) to a channel that previously had no detail, you can use channel mixer to swap channels.

Green to Yellow:

Basically 0R/255G/0B to 255R/255G/0B
or replacing the red channel with the green.

So in channel mixer:

Output Channel: Red

Source Channel: Red: 0 (takes all of the red channel away) Source Channel: Green: +100 (adds in the green channel)

Green to Red:

Basically 0R/255G/0B to 255R/0G/0B
or replacing the red channel with the green, as above, and then doing the opposite by replacing the green channel with the red.

So in channel mixer:

Output Channel: Red

Source Channel: Red: 0 (takes all of the red channel away) Source Channel: Green: +100 (adds in the green channel)

Output Channel: Green

Source Channel: Red: +100 (adds in the red channel)
Source Channel: Green: 0 (takes all of the green channel away)
DM
dave_milbut
Jul 11, 2004
The key word above is Basically.

yea, kind of… 🙂

thanks john. dave

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