Thanks folks. Option 2 is the winner so it will be implemented
However, I'd only like the stretch option to occur on linear data, of course -- is there the option to turn it off when perusing non-linear images?
File Explorer does this automatically. It only applies AutoStretch to images that require it, and the decision is made based on statistical properties of the data. This works very reliably. AutoStretch is never applied to a number of formats such as JPEG, PNG, SVG, BMP, PBM, XPM, etc.