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And the self darkening of the image is annoying and makes useless the image to correct a single pixel in Photoshop.

That sounds like a tonemapping problem. If you are using MaxWhite or Contrast, try switching to Linear or Reinhard.

If the image is darkened it means that some pixel is very bright, the intensity of this pixel is set to the max white level amd the whole image becomes dark or black.
The Reinhard is a compression of the dynamic range of the image that still has the hyper bright pixel, so the intensity levels of the image are compressed with the consequent loss of quality.
Reinhard is useful for see the progress of rendering, but never for the final image and many times the Reinhard image is also too dark.
The linear mode never works, the images are always black.
The correct solution would be remove the hyper-bright pixels from all the buffers and let the image with normal illumination.

Now are 80 minutes of rendering and all is going pretty well, and I have a good skin material.

Stupidity also evolves!