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Posted on 03/08/09 11:49:08 PM |
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Jessie711
* Posts: 24 Reply  |
Using the Channel Mixer Adjustment Layer
When using the Chanel Mixer adjustment layer are there any guidelines on how much to adjust each Chanel? One example given in Katrin Eismann’s book restoration and retouching she gives an example of, Red +110 %, Green +140 %, Blue -170 %. I think I understand how you can increase more than 100% but how do you remove more than 100%. Or am I missing something. Thanks Jessie |
Posted on 04/08/09 07:32:08 AM |
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Nick Curtain
Model Master Posts: 1768 Reply  |
Re: Using the Channel Mixer Adjustment Layer
Hi Jessie The composition of colour is a complicated subject and use of the CM is equally mind boggling. If you are using the tool in colour mode, then there are nine sliders, i.e. R, G & B within each of the three channels and these will give a variety of results. You may find it useful to open an image, a street scene for example and on one side fill three circles with pure red, green and blue. For example, pure red will be Red 255, green 0 and blue 0. Then open a CM adjustment layer and the default will be the red channel. Move the red slider and you will see than in the red circle nothing will happen beyond 100% because red is already 100%, but decreasing red will force the red circle to black. The same applies to green and blue when you move those sliders within the respective channels. While doing this see what happens to the street scene at the same time. Now experiment by using say the blue slider within the red channel, or the green slider within the blue channel and see what happens. Mono: Each image is made up of red , green and blue and these will always total 100%. When you click monochromatic, Photoshop will tell you how the RGB is made up. By altering the sliders, the make up of the image will change, so for example, if you wanted to darken a sky you would reduce the blue slider however, because all subjects within the image are likely to be made up of a percentage of R, G & B, then moving the blue slider will affect them too, so you have to compensate by increasing the red and green channels. I think the key here is to follow the rule (not cast in stone though) that the channels should add up to 100% and just experiment. In later versions of PS there is a B&W conversion Adj Layer, which I find much more intuitive and I rarely use the CM now. Hope this helps. Nick |
Posted on 04/08/09 5:07:32 PM |
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Jessie711
* Posts: 24 Reply |
Re: Using the Channel Mixer Adjustment Layer
Thanks Nick that certainly gives me a better understanding of how the CM works. I think it’s time to experiment a little. Jessie |
Posted on 22/08/09 03:47:51 AM |
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tank172
ThreeDee Thriller Posts: 692 Reply  |
Re: Using the Channel Mixer Adjustment Layer
Hi Jessie, As far as deciding how much to move the sliders, it might help if you have the Histogram opened while you're making the CM adjustment. I really haven't played with Channel Mixer in RGB, but in CMYK for newsprint, it's been a very useful tool. I mainly use it to slightly pull back Black from CMY and boost Black on K using the same numbers in each. This helps create better color separations on press and at the same time reduce total ink densities. You can use the same method above to boost color in each channel as well as reduce the black. Another tip, if you are creating a "color pop" image and require the black to be 100%K instead of 4 color black, you can make a selection of an area you want only to print Black (100%K) --> create a new Channel Mixer Adjustment layer --> and check the Monochrome button --> ramp up Cyan to taste (if you have shades of gray in the black area). That will remove black from CMY and put it only on K. By using an adjustment layer, you can now create a "color pop" image that will print properly on Newspaper stock. That's about all I know about the Channel Mixer. While you may never need to use what I described, it could help another browsing the forum.  You can also use it for advanced colour corrections on an image.
Hope this makes some kind of sense... Regards, -Chris |