Remove gradual "whiteness" of the picture

[pygmalion]

This problems bugs me so often, I decided to post a question here.

I usually correct the whiteness of the pictures by using Level / Pick white point tool.

However, so often the "whiteness" of the picture changes gradually over the picture.  Is it possible to correct "whiteness" gradually all over the picture?

Thanks for your suggestions!

https://i.imgur.com/e7Y6Q1D.jpg

[Ofnuts]

Possible solution:

* With the color picker, sample the lightest and darkest background color, and assign them to the FG and BG colors
* Add a layer filled with white, and set it to Divide mode (so the end result is your initial image)
* Set the gradient to FG to BG (RGB)
* Create the gradient between your two sample points. In Gimp 2.10, you can adjust the position of the gradient endpoints to get the best match. And if your light source was close, using a radial gradient (centered on the lightest point) could be an even better approximation (done below)
* If the effect is too strong, reduce the opacity of the the "Divide" later

   

This said, as an amateur photographer, I would say that you could avoid the problem with a light source farther away or with a big diffuser/lightbox.

[pygmalion]

Thanks for the instructions - pictures are now much better.

The lightsource was actually the Sun, indirectly, by reflection from different white walls. This is the best I can do to get uniform lighting.

[Ofnuts]

(04-06-2020, 03:04 PM)pygmalion Wrote: Thanks for the instructions - pictures are now much better.

The lightsource was actually the Sun, indirectly, by reflection from different white walls.  This is the best I can do to get uniform lighting.

You can put a cardboard covered with aluminum foil as a reflector to get some light from the back. A large saucepan lid can also do the job.