2.10 Levels tool: Add a way to perform Auto Input Levels while preserving color
Description of the feature
The Auto Input Levels button in the Levels tool sometimes (but not always) works much better than Stretch Contrast. However, it currently has no way to operate on the Value "channel" as a whole, rather than the individual RGB channels.
Operating on individual channels provides a useful white-balancing effect, but sometimes color shifts are undesirable. Right now, the only solution is to manually adjust the input levels to fit the histogram. A checkbox or separate button to keep color, as with the Stretch Contrast tool, would help immensely.
It would be nice to make this hypothetical change affect the Value "channel", rather than each individual channel, to make it easier to edit the adjustment afterwards.
Example
Take this image.
With the Auto Input Levels button, it looks like this:
Leveled manually with the histogram to match:
The desired level isn't always obvious on the histogram. (This is on a different image.)