I would like to to change the saturation of all the color of an image to a fixed amount retaining the original hue and brightness.
One could think that this is easily achieved by the sautration blending mode. In fact you can read on the web tutorials things like this:
The Saturation blending mode applies the saturation of the blend color to the base image while retaining the hue and luminance of the base image.
But this is actually false as far as I can see. If I use a 100% saturation blend color the resulting color will not have 100% saturation and the resulting saturation will also depend on the brightness of the blending color.
So what is the "saturation" mode doing? Is there a way to change the saturation of the color of an image to a given desired amount (retaining original hue and brightness)?