XnView Software

Curves is a mighty tool, but to unleash its full power for RGB correction, it needs the histogram as background like in Levels.
Compare it with Gimp:
https://docs.gimp.org/de/gimp-tool-curves.html

With a histogram, Curves can do what Levels does - and much more!

In a precise, visual guided manner (and not only as trial and error playground).

+1

another thought is that about mixing the Luminosity and RGB adjustment in one session. Now we can only choose either Luminosity or RGB, can not work with both.

+1

See issue for current status and some details.

This problem is supposed to be fixed in XnView MP 1.6.0. Please check and confirm the bug fix here.

It works