Use the ScaledBrightnessARGBConverter to display ARGB image in the BDV

[tinevez]

With this converter, the control slider of ARGB sources controls the brightness of the display. This is better suited for segmentation overlays in the shape of label images. For instance:

[tinevez]

This requires the PR argb converter in the imglib2 repo

[tpietzsch]

I see that this is convenient, but it breaks the semantics of the min/max slider:
The slider "min" is not used to offset brightness as for the other converters.
The intensities are scaled by "255/(max-min)" which is exactly the opposite as for the other converters.
This is in particular problematic because these sliders will manipulate multiple sources at the same time (if multiple sources are selected) and would have opposite effects on ARGB sources and other sources.

So I don't think this is how it should be done.

I would rather have a separate way from min/max sliders. Maybe have contrast and brightness (or rather scale and offset) sliders, where contrast would directly control the scaling factor. This can be converted to min/max values (except contrast=0 would mean max=∞, but close enough). So wouldn't need to change much under the hood. Basically just a UI toggle of whether you want the min/max or scale/offset sliders.