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Hi. Please let me know if I am right - I was wrong in my above assumptions, I believe.

The transformation takes a narrow range of grey-level pixels in the input image and maps them into a wider range in the output image.

So, in a Fourier spectrum, for example, the dominant white pixels will become more grey and the unseen black, or near black, will become visible. So, it lessens large variations in pixel values.

Why is this useful. Is it used for things like making image negatives? So, for example, if I were to perform the inverse log transform, would this make a negative image which would be useful in things like mammograms?