I have been trying to replicate the effect of Gimp Levels tool in blender but could not quite get the same result as in GIMP. My attempt is summarized on the picture below, I tried to remap the values to a new range but that did not really work. Any idea how to achieve the same effect?
The upper part of the Levels tool, "Input Levels",
should be equivalent to mapping the "Value" channel of the input image to the output image through a ColorRamp:
Separate HSVA, then recombine them with Combine HSVA, but add a Color Ramp between the V sockets. In the Color Ramp add a slider ("+") and moving the three sliders should behave the same as in Levels.