So, there is no obvious checkerboard...however, there is DEFINITELY structure in there...I see some kind of horizontal correlation or something going on, often between more than 2 pixels, which is interesting (if it was just 2 pixels, I could possibly understand that if the pixel architecture was a 2-shared (2x1) or 4-shared (2x2 pixels sharing one set of readout circuitry) design). I suspect that is what your FFT is picking up on. This is not the first time I've seen horizontal correlation between pixels, but usually it is just a couple of pixels.
Yes there is some structure - well spotted!
If I perform a PixInsight SplitCFA on sn2006gy's master dark and measure the standard deviations in each channel I see the following:
This clearly shows channel scaling. But there are no histogram gaps or histogram spikes of the type we see on Nikon cameras with white balance pre-conditioning, so it could indicate that this channel scaling is applied before digitization.
CFA1 is the channel with the weird diagonal stripes in the FFT, so given CFA0 and CFA1 have very similar stdDevs we can safely deduce that the "weird" channel is one of the 2 green channels.
Edited by sharkmelley, 29 December 2020 - 03:59 AM.