you have to look at the images at their full resolution in order to appreciate the difference.

As discussed during May 13th hangout, considering you focus on VTK6 integration. We are re-targeting this issue for 4.5 release.

In case you plan on addressing some of these for 4.4, consider re-targeting.

Re-evaluate this after Slicer switches to VTK8.

@kikinis Using the nightly build, is this still an issue ?

This particular issue is gone. However, when I switch from GPU to CPU Volume rendering, the rendering gets darker

I still see a very significant difference in image quality when I switch between adaptive/max quality. See attached files.

The screenshots above were created on Windows 10, latest nightly build downloaded from download.slicer.org.
CTACardio sample data set, CT-Cardiac3 preset.

Somewhat related: on my laptop (Windows 10, Surface book), if I switch to 3D-only layout and enable maximum quality volume rendering, then the application windows stops updating. Popups are still displayed, mouse cursor changes shape, etc. but no content update. The same problem is not reproducible on my desktop (Windows 10, NVidia GTX 1060).

We've switched to VTK9 and improved rendering techniques (adaptive, normal, maximum quality). Adaptive and normal should provide very good quality rendering for general use, while maximum quality can be used for generating screenshots.