Not sure what you’re trying to achieve here. Are you putting together files to demonstrate how Lab works?
To have each channel on it’s own layer. WIth your document in Lab mode do the following:
Duplicate the image on three layers.
Set your background colour to RGB = 127,127,127
Delete the a and b channels from the bottom most layer (this becomes your "L" layer
The two topmost layers will become the "a" and "b" layers, delete the b and a channels, then set the background colour to white and delete the L channel.
Set the two topmost layers to Multiply
Since you’re in Lab mode, I’m not sure what this accomplishes…
Yes, I’m trying to demonstrate how Lab works. Though I’m not sure if it’s possible.
Nomad, with "Set your background colour to Neutral Gray", do you mean the background color swatch in the Tools pallete or do you mean fill the background layer? What does it do?
The bottom layer will be the L layer?
I’m doing this all in Lab mode?
Again, I’m trying to make the separate layers resemble the actual colors. In a CMYK image this would mean you have a Cyan layer, a Magenta layer and so on.
In Lab this means you have a "Dark=Green to Bright=Red" layer and a "Dark=Blue to Bright=Yellow" layer.
I’m trying to achive this by using Gradient Map adjustment layers. So the layers by themselves look correct. I just need the blending modes.
Also I’d like to know for sure if it’s Green to Red or Green to Magenta as I’ve read both. Right now I’d use:
R=255 for red;
M=100% for magenta;
G=255 for green;
B=255 for blue;
Y=100% for yellow.
Maybe there is a mistake. Of course it’s either red OR magenta, not both.
Thanks!
It’s Green to Magenta, as Dan Margulis so aptly demonstrates in his wonderful book on Lab color – The Canyon Conundrum. You may gain a lot of insight simply by reading his book and looking at the illustrations there. You may be trying to reinvent the wheel here.
The red/green or magenta/green designation is simply a visual description and has nothing to do with how red or magenta are defined in RGB or CMYK. You can decide for yourself if "that color" looks red or magenta. As to how those colors match each other going between Lab and RGB/CMYK, try this: In a Lab document, fill with grey. In curves, select the a channel, and move the left end point up as you observe the changes in the info palettes. You will see that you are moving towards red and towards magenta, but neither is pure, the magenta being contaminated by yellow and the red being contaminated by blue. However, you are moving more in a magenta direction than in a red direction.
Jonathan Clymer
Yes, it’s green to magenta. They are complimetary colors – that is, they are exactly 180 degrees opposed from one another on the color wheel. The complimentary pairs are:
green – magenta
red – cyan
blue – yellow
Regarding the need to demonstrate how lab works, why not just use a Lab file? If you do your demo from within Photoshop, you can show in real time what happens with a lab file. I know what you’re doing with the CMYK/multiply file (as well as the RGB/screen file.) You can’t do a similar thing with Lab. Blending modes will not simulate how Lab works; the math is radically different.
I second Peter’s recommendation to read Dan Margulis’ book on Lab (The Canyon Conundrum.) It’s excellent and eye-opening. You don’t actually have to read the entire book to get the jist of what he has to say.
Thanks to all of you this already was eye opening, I’ll read it.
background color swatch in the Tools pallete or do you mean fill the background layer? What does it do?
I mean the backgrond colour swatch
Gotta run
Sorry about that, the shan hit the fit at work.
What I mean was the background colour swatch, that way, when you hit delete on the a and b channels, you end up with the colour that is neutral in those channels
