@Manuel_Angel - thanks for supplying these images from your setup! The circle of people having a little bit of noise in their captures widens! Here’s the red channel of your capture with the shadows pushed up into medium gray:
As you can see, there is a tiny bit of noise on the right side of the frame. Very similar to my captures!
Your empty film gate image shows no banding at all - that was what I was suggesting: the noise is only present in the dark areas of the image, not present in medium or high intensity ranges.
@jankaiser - thanks as well for joining the group!
All of what you listed here gets rid of this noise:
- “lowered the exposure”, i.e. keeping the dark shadows dark, not pushing them too much into medium brightness levels.
- allowing me to rephrase “processed video frames” into “encoding into H264/H265”: video compression usually hides this noise quite effective. It simply gets kicked out by the compression algorithm.
- “colour noise reduction step” is my favorite angle of attack. Spatio-temporal denoising gets rid of the noisestripes for sure.
Many thanks to both @Manuel_Angel and @jankaiser for your fast reaction! Taking into account the diversity of the scanners, their difference of the surroundings with respect to EMI and the various illumination sources employed, by noting the similarity of the noise patterns, I think the verdict is clear: this noise is mostly a peculiar property of the IMX477 sensor chip used in the HQ camera.
Different strategies to counter this effect have been already proposed and discussed in the Strange encounter in the red channel/RPi HQ Camera-thread, so I will not repeat this discussion here.