Z7 PDAF banding technical discussion

Started Oct 18, 2018 | Discussions thread
Horshack Veteran Member • Posts: 9,795
First controlled banding reproduction setup

I have my first fully controllable and reproducible banding setup, where I can:

  • Induce banding 100% of the time at one shutter speed (1/50)
  • Induce variable shot-to-shot banding (30% of the time) at the next slower shutter speed (1/40)
  • Zero or near zero banding frequency at a slower shutter speed (1/25)

I've done lots of iterations between size of light source in frame, brightness of light source, and where the light is positioned. I still have more a bit more work to fully isolate each of these factors, but for this one setup I can fully control the banding occurrence from 100% to near 0% with just 1EV of shutter adjustments.

Here's my setup: A Dracast LED light (dimmable with digital dial) and barn doors, with the Z7 about 2.3' away:

Z7 Repro Setup

Here's what the banding looks like at 1/50, compared to a non-banding frame at 1/40. 100% crop. Press "original size" to animate:

Banding at 1/50 vs non-banding at 1/40. Click "original size" to animate

And here's what the full scene looks like for the above two crops:

Full scene of banding shots. Click "original size" to animate.

The banding manifestation is some combination of the relative brightness of elements within frame. Again, I have more work to do in isolating light source source, position, etc... as factors. But to my eye this is looking possibly algorithmic in nature, ie something in the Z7 firmware (or hardware) is keying off these factors to adjust how the image is captured/ADC configured and that has a side effect of the banding.

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