r/GIMP • u/BKNRED • 2d ago

Colour to Grayscale conversion while maintaining contrast/perceptual brightness

I am looking for a method to maintain the contrast and perceptual luminosity of an original colored picture/image. Sorry I had to use an external host to maintain pixel accuracy.

I did a little test with a sprite from Brackey's Godot tutorial. Can you give me your advice on the closest to the result I described ?

To me none of them has got exactly the same contrast/luminosity as the original picture.

1 - IrfanView - Convert To Grayscale option (included just cause)

2 - Gimp 3.0.2 - Desaturate -> luminance

3 - Gimp 3.0.2 - Desaturate -> HSL lightness

4 - Gimp 3.0.2 - Hue-Saturation - Saturation slider down to -100 Blending Mode set to HSV Saturation

Original

Ensemble

For the closest I think it's luminance

Is there a better way to achieve the result I am seeking please ?

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u/ofnuts 1d ago

"Luminance", "lightness" and such are just combinations of the RGB channels with accepted coefficients. You can make up your own combination using Colors > Components > Mono mixer.

But on such small images, the perception is very dependent on the surroundings.

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u/BKNRED 11h ago

Ok thank you very much for your input. That puts the process into perspective.

I guess that I can give up on a "one size fits all" setting to convert hundreds of color images to grayscale ?

Maybe I can sort the images according to some criteria and find best settings for each groups ?

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u/ofnuts 11h ago

IMHO You are overthinking it for such small images and one size actually fits all 😇