I'm having trouble understanding the meaning of what's going on in the steps for setting up the blue midtones of an image for adjustment. I just had a bit of a revelation when I was examining the names of the layers in figure 3.33, and now I realize that the steps separate the blue channel into two layers: the midtones and the highlights/shadows.
So, now I guess the part I don't understand boils down to how "Group with" works. My understanding is that when you group one layer with another, only where there is content in the lower layer will content in the upper layer be visible. That seems to fit what is happening for the Blue Midtones group of layers on p.88, but when I apply that concept to the Blue Highlight/Shadows group, I can't make sense of it. It seems to me that since there is content everywhere in the lower layer-- the Blue Highlight/Shadows layer--all the black pixels in the Blue Mask layer should be visible.
But then, why is the Multiply mode necessary for the Blue Mask layer? I understand Multiply will turn every midtone color in the lower layer to black because (0,0,0) multiplied with any other pixel color is (0,0,0), but why doesn't "Group with" and the Normal blend mode accomplish the same thing? I know it doesn't from experimentation, but I don't know why, and that's why I guess I don't understand "Group with".
Oh, and one more thing. I find that when I use Curves to create the masks, I can't map, say, 74% input to 0% output while simultaneously mapping 75% input to 100% output: Curves will only let me use the input points 73% and 75% or 74% and 76% but not 74% and 75%. I've played around with curves a bit to make several masks based on tone, and once in about 5 tries I'm able to use consecutive input points, but usually it won't work.
Thanks
So, now I guess the part I don't understand boils down to how "Group with" works. My understanding is that when you group one layer with another, only where there is content in the lower layer will content in the upper layer be visible. That seems to fit what is happening for the Blue Midtones group of layers on p.88, but when I apply that concept to the Blue Highlight/Shadows group, I can't make sense of it. It seems to me that since there is content everywhere in the lower layer-- the Blue Highlight/Shadows layer--all the black pixels in the Blue Mask layer should be visible.
But then, why is the Multiply mode necessary for the Blue Mask layer? I understand Multiply will turn every midtone color in the lower layer to black because (0,0,0) multiplied with any other pixel color is (0,0,0), but why doesn't "Group with" and the Normal blend mode accomplish the same thing? I know it doesn't from experimentation, but I don't know why, and that's why I guess I don't understand "Group with".
Oh, and one more thing. I find that when I use Curves to create the masks, I can't map, say, 74% input to 0% output while simultaneously mapping 75% input to 100% output: Curves will only let me use the input points 73% and 75% or 74% and 76% but not 74% and 75%. I've played around with curves a bit to make several masks based on tone, and once in about 5 tries I'm able to use consecutive input points, but usually it won't work.
Thanks
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