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In GIMP, is there a way to control a gradient brightness and/or contrast of a selection? The application is this: I'd like to control the brightness/contrast of one end of my selection to match a darker area of a particular image, while also controlling the brightness/contrast of the other end to match a lighter area of the same image while obtaining a smooth transition between the two ends. Thank you, in advance.

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You can paint on a transparent layer and then apply brightness contrast.

But there are possibly better ways:

Gimp 2.8

You can sample the colors on both points to set the foreground and background color, and the use the FG to BG (RGB) gradient.

Gimp 2.10

  • Start the Blend too and click and drag to create the gradient
  • You can then click on any extremities to make it editable in the small on-canvas dialog
  • In that canvas you can edit the color in a color selector (click the color button), and this changes the displayed gradient.

So you can very easily match the colors of the extremities

  • Cherry on the cake: if you click on the gradient line near the middle, you can grab the gradient mid-point and then move it to adjust the gradient curve.
  • 2nd cherry on the cake, if you click somewhere else on the gradient line, you create a gradient "stop" and change the colors on both sides.

So in practice you can fully edit the gradient that you are creating.

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  • Thank you so much Xenoid for your insight. I am currently using GIMP 2.10.12. I will pursue your advice. I do not fully understand it yet, however, with some Googling, I believe that it will become clear to me. My Gimp/Photoshop knowledge is blotchy.
    – Tim OHeron
    Dec 29 '19 at 1:24
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You can make to separate layers two copies A and B of the image that should have sliding brightness and contrast. Adjust A and B to match with the different edges of your reference image.

Let A be ok in the left and let B be ok in the right.

Drag A to the top and insert a layer mask to it. Let B be the next layer downwards.

Insert a left to right gradient from white to black to the layer mask of A. You may have to experiment a little with the stops of the gradient. Alternatively you can apply curves to the layer mask. Before clicking OK tweak the curve for best match.

I guess you have a good reason to avoid Photoshop, where one could simply use a curves adjustment layer with a gradient mask and "next layer only"-switch=ON. But that functionality can be found also in freeware. It's in web application Photopea and it can be found in Krita.

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  • Thank you User287001. I have a very old version of Photoshop (circa 2000 lol) but since I do not use this professionally, my budget is limited to the Open Source GIMP. Thank you for the insight that you have provided. I do understand this and will give it a try and your help is very much appreciated. Please have a happy New Year.
    – Tim OHeron
    Dec 29 '19 at 1:27
  • PS7 is still worth using
    – user287001
    Dec 29 '19 at 5:06

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