: Levels/curves/gamma gradient in photoshop I have a raster image with an obvious gradient of exposure and contrast from top to down. I can easily find perfect adjustments using Photosho/Image/Adjustments/Levels

@Hamm6457569

I completely agree with Neo (thanks) that imaging postprocessing can often be done best in the source application or in ImageJ. But sometimes it is not possible.
After searching and trying for several hours, I actually just now found an (at least at the first glance) easy solution within photoshop:


layer / new adjustment layer / Curves (or whatever is desired) --> adjust sliders --> affects range/gamma/etc. of the WHOLE image. But then,
in the gradient map layer "flyout" (see screenshot), click "Masks"
in the gradient tool box, select e.g. a linear white-to-black gradient, and draw it at the desired direction and part of the image, e.g. from bottom left to top right according to the exposure inhomogeneity... voila!


Finally, needless to say, that imaging postprocessing should not be abused but communicated to the readership if applicable.

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@Lee3735518

Unfortunately what you want to do is not possible in Photoshop, this is called local contrast normalization and it is used for example in biomedical imaging to bring the image, or other type of signal, into a range that is more familiar or normal to the senses, hence the term normalization. Often, the motivation is to achieve consistency in dynamic range for a set of data, signals, or images to avoid mental distraction or fatigue. For example, a newspaper will strive to make all of the images in an issue share a similar range of grayscale.

This problem is easily solved in the field of Computer Graphics, where you can find computer algorithms and specialized software that makes the process of grayscale conversion more friendly.

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