Ah yeah, I recently changed the url scheme for my blog posts, from

    https://daniel.lawrence.lu/blog/y2025m09d21

to

    https://daniel.lawrence.lu/blog/2025-09-21-line-scan-camera-image-processing/

so maybe that's why OP didn't realize that it had already been posted recently. With the older scheme, not only is SEO bad, but it was really hard to remember which date corresponds to which blog post, and people can brute force search for my hidden (unpublished) blog posts easily.

The gain is fixed. I think the column variation arises from unstable oscillator frequency and maybe some electrical bug/crosstalk between pixels. Not sure exactly.