[Gambas-user] Color Range

Claus Dietrich claus.dietrich at freenet.de
Tue Jul 25 20:22:35 CEST 2023

Am 25.07.23 um 14:28 schrieb Gianluigi:
>> Hi Gianluigi
>> Thanks, I am aware of it and use it a lot.
>> I had a closer look to gb.image.effect, which offers the methods 
>> "Normalize" and "Equalize". The spectrogramm showed me, that 
>> "Equalize" is getting close to what I am looking for, but it does it 
>> automatically and for all colors. The context-description of the 
>> method "Normalize" also fits to my requirements, but its visual 
>> effect is very small and it also works fully automatic and for all 
>> colors.
>> Is there any known documentation about gb.image.imlib?
>> Best regards
>> Claus
> It's not clear to me if you want to do something like this (*)? Maybe 
> you should explain the problem better.
> Best regards
> Gianluigi
> (*) see link : https://paste.c-net.org/GymnastCylinder
Hi Gianluigi

Its all about my Gambas scanner program, which after years became pretty 
mature and it's doing a fantastic job for documents and photographs. But 
now I am planning to digitize tons of aged paper photographs (I guess 
more than thousand). Normally I use two dialogues within Gimp (see 
attached screenshots) to correct the ageing effects. The one shows the 
spreading of the color range (showing a typical spectrogram for red of 
an old photograph as reference) while the other provides an adjustment 
of the color curve, with a spectrogram in the background for 
orientation. Normally I do adjustments for red, green and blue 
separately. To do this for more than thousand photos in a separate 
application would be crazy. Like in good scanner apps I like to be able 
to do exactly this within my app. Post corrections for Lightness, 
Contrast and Gamma are already implemented but they cannot compensate 
ageing effects.

I already tested a post correction for aged photographs with the fully 
automatic "Equalize" method, but the results are unpredictable and are 
ranging from good to very poor. I compared this method with Gimp and 
found, that the results are identical to those of the Gimp's 
Auto-Contrast feature, which is not what I need.

Hope that someone has an idea, how this can be done within Gambas.

Best regards


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