Meridian flips and sequence background extraction

Software Siril
1

In the past using Siril, I have never made any distinction between images shot before and after a meridian flip - they all just get processed together and Siril rotates the later images to match the orientation of the earlier ones. I would then apply a background extraction to the final stacked image.

However, with the new ability since v0.99.4 to apply background extractions on the entire sequence, it seems to me that separating pre- and post-flipped images into two separate sequences (or at least treating them separately) would now make sense, as one would expect the background extraction to be different for these two sets of images.

Would this be correct?

2

No because background is computed for each image.

3

Right, but wouldn’t the squares be in the wrong place for the flipped images?

So for something like the Horsehead Nebula, you would remove any squares on the nebula for the pre-flipped image, but those squares are not necessarily going to exclude the nebula on the post-flipped images.

4

Removing background extraction in a sequence we advice user to use first degree polynomial function. At first degree, there are generally no problem of excluding something we don’t want ;).