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Add adjustment, say Curves, to photo. Edit Blend Ranges/Options (cogwheel) within the adjustment. Don't adjust the curves.

Editing both the left (source layer ranges) and right (underlying composition ranges) -- both have an effect.

So I'm wondering, what's going on here? What is the difference in effect between the left/right graphs in this situation?



Dave Straker

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Dave... This has always confused me, as well. I think I understand the difference (but, honestly, this is only a guess). I think of the Adjustment and Live Filter layers as having a value going in (that is, the RGB values presented to the adjustment layer) and then a value coming out (the RGB values after the adjustment has been applied). The graph on the right (underlying layers) tells the adjustment only to work on specific values coming IN, while the graph on the left (current layer) effctively limits the adjustment to work only on pixels that give a specific RESULT coming out.

As an example, imagine I have a grid of numbers, and they are all between 1 and 10. I have an “adjustment” layer that adds 2 to every value. I can use the right graph to assure that I only allow numbers 6 or greater into the adjustment. That would result in a grid with numbers between 1 and 5 (the ones that the blend range did not allow into the adjustment), and other numbers between 8 and 12 (the ones that were allowed into the adjustment layer, and had 2 added to the original number.


If I have that same grid of numbers 1 to 10, and the same “add 2” adjustment, I can use the left graph to limit the action of the adjustment based on the numbers that come OUT of the adjustment. Without the blend range setting, numbers between 1 and 10 went IN to the adjustment, and all were increased by 2, what comes OUT of the adjustment is a bunch of numbers between 3 and 12. If I use the left graph to limit the adjustment to results that are 6 or greater, then I am telling the adjustment ONLY to apply to any number that would result in a value greater than 6 as OUTPUT. In effect, this means that only the grid values between 4 and 10 are allowed into the adjustment. So, what I see with that adjustment in place, and the left graph active, is a grid of numbers between 1and 3, and also values 6 to 12. The original grid values of 4-10 were allowed to have the adjustment applied, and gave values between 6 and 12. The original grid values of 1-3 were not allowed to have the adjustment applied, and they remain unchanged.


The results of the left graph and the right graph are subtly different.

All that having been said, it is an awful lot of mental math to try to keep straight, and I have yet to find ANY practical use for using the left graph (current layer) on an adjustment or live filter layer. And I have also not come up with any situation where I wanted to use BOTH graphs on the same layer.

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