I am trying to figure out how one can select an area and get a grayscale as a result. But I don't even know what to do with the grayscale.

I have created a simple gradient, to create an example for this question.

Gradient 1

And I want to turn it into this gradient.

Gradient 2

This would be straight forward, you'd just swap the red channel with the blue channel.

Yes, this would be that. But what I want to obtain from this question, is to figure out an alternative way.

Modifying the Channels directly, seems destructive if you have something entirely different.

What if there wasn't only green, but also yellow and you want to turn the red accurately into blue?

This is why I want to figure out a different method, that solves that question.


I have tried taking the red mask, and tried to do Layer Blending with a RGB (0, 0, 255) color (full blue).

But it's not giving the output at all, and still keeps red.

What is the way, that focuses on the question regarding what if there would be yellow or any other color? (If you have an answer that isn't destructive for the one without the yellow then it answers the question as well)

Like, turning this:

enter image description here

to this:

enter image description here

but not destructive, or just a section of it by using a mask

This question should aim for solving situations where you want to colorize something and manually selecting the area. And a color could be overlapping with another. If you'd fully put a white pixel in the mask, the colorize strenght would be more than what it is on the original image.

  • 1
    Switching channels is nondestructive. The result might be weird, but it is totally reversible.
    – Rafael
    Commented Oct 9, 2023 at 16:07

1 Answer 1


It sounds to me like you are looking for Adjustment Layers. These are a non-destructive way of applying edits, and they come with a layer mask which you can edit to exclude certain areas.

Here's an example using the Channel Mixer as an Adjustment Layer, with a mask applied to limit the adjustment to the red area only. The button highlighted in red is where you can find and add Adjustment Layers.

enter image description here

Another method would be to use a hue-saturation adjustment layer.


To edit the layer mask, select the layer mask thumbnail in the layer adjustment to highlight it. Make a selection and fill it with black. Areas which are black will not have the adjustment applied. Alternatively, you can also make a selection before adding a layer adjustment, and it will be added to the mask automatically.

As for the Channel Mixer, here are the settings I used for the red green and blue channels. Obviously you can tweak these as you like.

enter image description here

EDIT You could also use a Hue-Saturation adjustment layer similarly.

enter image description here

  • Isn't there still red left? Commented Oct 9, 2023 at 12:01
  • @karl-police - what do you mean? Can you see any red in the image? The original layer hasn't been changed. The change is applied using a layer adjustment. If you hide the adjustment layer, you will see the original is unaffected. The adjustment layer is basically swapping most of the red channel for blue.
    – Billy Kerr
    Commented Oct 9, 2023 at 12:16
  • @karl-police You could also use a Hue-Saturation adjustment layer for a similar effect. see example.
    – Billy Kerr
    Commented Oct 9, 2023 at 12:24
  • I see red. I don't want to simply turn it into blue. I want to precisely turn it into blue. One way would be swapping the channels, but that's destructive because it's a change that you can't undo if you proceed unless you swap the channels back assuming no other colors are added or something. I wanna turn it to blue but keep all the levels. Commented Oct 9, 2023 at 12:30
  • @karl-police Where do you see red? None of the edits shown in my examples are destructive. You can simply hide the adjustment layer to remove any effect.
    – Billy Kerr
    Commented Oct 9, 2023 at 12:33

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