Can you think of a nifty trick to work in grayscale, while previewing in real-time a 2 color separation?

Question

I need to come up with a procedure that allows a customer to work on a black and white image while assessing the effect of a translation into a 2-color separation.
To visualize what I’m looking for, place a grayscale image in the magenta channel of an empty (white) cmyk document, and the same grayscale image inverted into the yellow channel. The other 2 channels stay empty (white).
Now we have the white end of the grayscale expressed as yellow, the black end as magenta. Since one channel is a direct inversion of the other, the sum total of the 2 is always 100% at any point along a gradient.
I have written a action, that allows one to quickly look at the effect, but what I am being asked is to is to deliver the same thing in real-time.
Duotone? NO!
In a duotone document I can only move one curve at atime, thus creating overlap (too much red) or a gap (whashed-out hue) between the profiles of the 2 curves.
CMYK? NO!
In a cmyk document I have the option to move 2 curves simultaneously, but what I would need is an option to work one curve, while the other automatically moves equally in opposite.
Gradient mapping?
Here I have a rudimentary way to set the starting, mid, and endpoints, but it needs to be done in RGB and I don't know of any way to separate the resulting RGB channels into a grayscale that maintains all the information.
Anyone? Any ideas are much appreciated.

Answer 1

Mars_Red wrote:
I need to come up with a procedure that allows a customer to work on a black and white image while assessing the effect of a translation into a 2-color separation.
To visualize what I’m looking for, place a grayscale image in the magenta channel of an empty (white) cmyk document, and the same grayscale image inverted into the yellow channel. The other 2 channels stay empty (white).
Now we have the white end of the grayscale expressed as yellow, the black end as magenta. Since one channel is a direct inversion of the other, the sum total of the 2 is always 100% at any point along a gradient.
I have written a action, that allows one to quickly look at the effect, but what I am being asked is to is to deliver the same thing in real-time.
Duotone? NO!
In a duotone document I can only move one curve at atime, thus creating overlap (too much red) or a gap (whashed-out hue) between the profiles of the 2 curves.
CMYK? NO!
In a cmyk document I have the option to move 2 curves simultaneously, but what I would need is an option to work one curve, while the other automatically moves equally in opposite.
Gradient mapping?
Here I have a rudimentary way to set the starting, mid, and endpoints, but it needs to be done in RGB and I don't know of any way to separate the resulting RGB channels into a grayscale that maintains all the information.
Anyone? Any ideas are much appreciated.
Mars Red,
This might work. Assuming you now have a CMYK document, with no cyan, no black, and magenta and yellow are inversions of one another
1. Create a solid yellow fill color layer on top, blend mode normal 100% opacity
2. Create an empty layer on top of that, blend normal, 100% opacity.
3. Select all, fill this layer with solid magenta
3. Hide this and the yellow layer
4. Load the magenta channel as a selection
5. Click on the solid magenta layer, Layer - Layer Mask - Hide Selection
6. Show all the layers
7. Click on the mask on the magenta layer. You can apply curves to this mask. No matter what you do to the mask, the yellow separation will always remain an exact inversion of the magenta. You will always have 100% ink coverage in every area, no more, no less. The only catch is the mask is opposite the ink, so curve adjustment is opposite of ink behavior.
That is CMYK solution. Here is duotone solution, much simpler:
Assuming you have a grayscale image:
1. Mode duotone
2. Type duotone.
3. Ink 1 : color picker, CMYK, 100M (yields name Magenta)
4. Ink 2: color picker, CMYK, 100Y (yields name Yellow)
5. Ink 2 curve: 0 = 100, 100 = 0 (inversion)
6. Hit enter. Now you can make curve adjustments to the duotone channel (not the duotone curves) using Image: Adjustments: Curves. No matter what you do to the duotone channel, you will maintain inversions of magenta and yellow, and you will always have 100% ink coverage in any given area.