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Using the Tone Curve: RGB Channels

If you tap on the Mode tile, in the pop-up menu that appears, you’ll see another set of curve choices: the Red, Green, and Blue Point curves. You’d normally use these to either do specific color correction tasks (but you really have to understand curves, in general, fairly well before you do this or you could trash your image’s color big time), or for doing special effects (which you don’t have to be an expert to pull off). Probably the most common special effect using curves would be to create cross-processing effects for fashion photography or to recreate Instagram filter looks. When you choose one of these RGB curves, like Point - Blue, your Point curve appears onscreen just like a regular curve, but the diagonal line itself appears in blue (as seen here), so you know you’re working on just the blue channel. Tapping in the center and dragging upward adds more blue to the image in the midtones; dragging downward removes the blue, giving you more green (here, I created a slight S-curve for this effect). The other two channels work the same: Dragging the green channel curve upward adds more green; dragging downward removes green, thereby adding magenta. And, dragging the red channel up adds more red; dragging down adds blue (I created an S-curve for each of these channels, as well).

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