Strange rolling shutter artifact

I was recently flying in a small aircraft, and took a picture while on approach, with the propeller going relatively slowly. Regretfully, I had forgotten that my camera was still in electronic shutter mode, so the propeller got all bendy and wobbly in the picture.

Update: _DSF7473.raf (21.7 MB)

(License: Creative Commons BY-NC-SA)

In addition, however, there is a small sawtooth effect on the propeller that I can’t make sense of. It seems as if there was some interlacing going on, with different image rows skipping back and forth in time.

Is this how modern image sensors are supposed to behave? I hope that there are a few technical people around here who can shed light on what is going on there!

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Really interesting.
I t would be even more useful if you could share the raw.

Anyhow, modern sensors can have some various implementations of the electronic shutter, especially those realized through a stacked CMOS process.
One possible explanation for the above, I think, is that some sensors have a way to read the rows and/or the columns not sequentially, but in a sort of alternated way (e.g. 1-8-2-9-3-10-…). The reasons for these are essentially technical workarounds to improve the speed or size limitations, like the fact that a conversion unit (e.g. an ADC) may not be fit in the width of a pixel, hence the columns are not read sequentially.

Mine above is just a possible explanation, based on direct knowledge of some actual sensor implementation I have, but it’s not the only possible one. I haven’t looked deeply in the exif nor in any metadata, just looked at a 1:1 view of the picture.

It’s really cool to see some of these technical-low-level details showing up in some actual shots. Thanks for sharing.

No problem, I updated the original post with the raw file.

That’s definitely what it looks like. Perhaps some kind of speed optimization?

It’s possible. Sometimes it’s needed to pipeline the conversion operations, bundling rows/columns into groups, and often these groups are not contiguous, for area constrains.

I’ve seen the picture has been taken with the X-T2, which I don’t know directly (or very little), but I’m quite sure it was still a time when the rolling-shutter was not as advanced as today (namely, it was not a stacked CMS sensor, I think).
It’s also a non-bayer sensor, so the demosaicing can play a role (I’m referring, for instance, to the “halo” of noise surrounding all the fast moving parts of the picture).

…Anyhow… I’m just a bit more than guesstimating here… :smiley: I admit I don’t know the details of that sensor.
Anyhow… you also just reminded me that I’d like to do some of this bending experiments with my X100V… It would be cool to explore that as well…

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