Fading film image color restoration effect of equalize command in GIMP 2.10

Software GIMP
1

Hi,
GIMP has equalize command (histogram equalization algorithm) which purpose is thought as increasing the global contrast of images. However it has fading film image color restoration effect, which is little known, I think, because it is only side effect of this command algorithm. Adobe Photoshop also has same name command, however it does not have the color restoration effect. I suppose the reason is that Photoshop’s algorithm is “improved” for original purpose of this command. Therefor, GIMP’s algorithm has hue shifting defect in comparison with Photoshop, but this defect has unintended desirable effect for film color restoration.

I would like to show this effect here.
Following image is original. This is old faded positive film scanned image.

GIMP_equalize_Fig1
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Fig 1

Using “equalize” command.

GIMP_equalize_Fig2
Fig 2

The result.

GIMP_equalize_Fig3
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Fig 3

This effect is not always successful, as not intended, however in much cases it is OK for color restoration of faded film or photo print scanned images.

I hope GIMP developing team to keep this feature of equalize command and not to “improve” this algorithm.

2

Thank you for pointing out this feature. I am a long time user of GIMP for photo restoration and this feature’s usefulness had slipped by me. I just tried an image where other methods were not very effective and it worked well. One method I have used a lot is the auto input levels option in the levels tool. This often does a great job. It may be that when equalize fails then auto levels might help and vice a versa.

image

3

Thank you for your additional information.
I think color restoration effect of equalize command is very very powerful. It is a great pity that this feature is not well known!