Doublebishop, you did look at earlier screenies , didn’t you? 
The same way the normalize node does it. EDIT: the only problem with the normalize node is that it also adds an offset in order to hit the full range 0…1.
However, it wouldn’t work proportionally, that is it would darken most of the other pixels (depending on their distribution of course).
What it does is this:
I think this is proportionally and not unusual. I just don’t want to manually adjust the slope of this curve. An automatic aperture.
I see what you mean but I don’t think that image data is the same as audio data.
Why? The volume of sound is the brightness of a picture. The difference and advantage is that Blender does not automatically crop values>1.
Both value mapping and clipping are typical operations on images.
Scaling also.
i think the main issue is going to be how to get to that number and apply it - i don’t think this is possible in compositor. if you could get somehow complicated in compositor to one number for one image - the issue remains how to tell this the RGB Curve Y? Drivers maybe? But drivers in compositor seems not really great - i don’t use them since they get lost in NodeGroups.
But a dedicated image normalise/mapping Node. +1
mapping / clipping as far as i understand work the same for audio / image, both just data that gets mapped / clipped