Ugly blackshade (at 4fps), beta 6.2.3

[Michael Tiemann]

I did a blackshade with beta 6.2.3 at a variety of shutter speeds, including 1/4 of a second (to test blending the motion of different shutter speeds using HDRx). When I completed the blackshade, I was surprised and disappointed by the histogram shown on the GIOscope, which told me that I had essentially no pixels at the lowest level, but a prominent bump starting at 2, peaking at 3-4, and then going back down at 5 before disappearing. I wondered what it meant. Here's a test frame showing the X-frame at 3200 ISO. I'm just posting a single frame, but across several frames, the block dots appear as if fixed pattern noise. It is as if the blackshade said "calm down little pixel" and fixed it at a level of black that was not zero, but was not just-above-zero either. The fixed pattern noise is not nearly as obvious in the A-frame, but if you toggle between the two, you can see occasions where the dark pixels obvious in the X-frame are also darkened more than expected in the A-frame.

I haven't yet analyzed black shading at higher shutter speeds, but those GIO scope readings showed a prominence of pixels at level 1, fewer at level 2, fewer still at level 3, and mostly nothing starting at level 4. While I might be disappointed that there are any pixels lighting up the GIO scope when the lens cap is on, I am not surprised to see noise at the lowest 2-3 levels.

The R3D snapshot (A001_C004_1108FS.0000000F.R3D) is in the directory here: https://www.dropbox.com/sh/d949ttzrbj9oh1q/AADZtHiQHh-qxsUMTfdQKYASa?dl=0

Thoughts?