Dan Pavel
Member
I am trying to make a PS script that can be used for making the Adjustment Curves layer for the DNs intended for multi-layer gum prints. The problem with multi-layers prints comes from the fact that each gray value of each layer, even if the layers are identical, doesn't add lineary. In other words printing 2 overlaid layers each with the gray level "A" will not result in an image with the gray level "2xA".
Till now I think of taking one of the following paths in solving this problem:
Till now I think of taking one of the following paths in solving this problem:
- The simpler approach could be to print a 3 layers image, for instance, then to find the curve for it as it was an 1 layer print, to make a new DN with the curve applied, print it again in 3 layers, get another curve, and so on. Each curve should be closer to the to the proper curve and after repeating the procedure 4-5 times hopefully a good curve, close enough of the correct one, will result. It will be quite time-consuming and I'm not sure that the resuted adjustments will converge to the correct one or will be divergent
. However, it could work with identical layers.
- A better approach with identical layers could be to print the first layer, measure it, then the second overlaid layer and again measure the result. By comparing the 1 layer - 2 layers results a table could be made and one could read what level of gray should be used in each layer to have a desired level of gray in the final image. Based on it a curves adjustment layer applicable to each layer could be made.
- The adjustment curve could be split in 2 - highlights till mid tones and mid tones till black. The first printed layer should only cover highlights to midtone and everything darker than the mid tone should be printed as mid tone. The color/gum/bichromate ratio and the exposure time have to be adjusted accordingly. Being a single layer print an adjustment curve could be computed for it. The second layer should have more color and a much shorter exposure time to make it print everything whiter than the mid tone value as white. Hopefully an adjustment curve could be computed for it as well, using a table as in the "2" case. The final adjustment curve could be obtained by using the first half of the first curve (highlights) and add to it the second half of the second curve (shadows).