[Gambas-user] Color Range

Gianluigi gradobag at gradobag.it
Tue Jul 25 22:19:58 CEST 2023

Il 25/07/23 21:33, Benoit Minisini ha scritto:
> Le 25/07/2023 à 20:22, Claus Dietrich a écrit :
>> 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
>> Claus
> If you know the algorithm associated with the the image filter you 
> need, you can try to implement it by accessing the image RGBA data 
> directly, and use the FAST keyword to let the gcc compiler transform 
> your Gambas code into a faster version.
> As I understand the dialog box, you need to be able to define a 
> function that takes a color intensity between 0 and 255 and that 
> returns the new value, and apply that functino to a color channel.
> Please confirm my interpretation!
> Regards,

ubi maior minor cessat :-)


¡ɥɓᴉs ¿ʇǝʎ ɹǝʌo sʎɐpᴉꞁoɥ ǝɥʇ ǝɹɐ

With best regards to all


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