Okay, so thing with computers is that they can only store numbers up to a certain precision. For example the number 0.3 is probably stored as 0.30000000000000004. So when we do operations, this outcome will be different than what is expected. This also paves a way for rounding errors, division errors, error over errors as we stack up operations.
Ideally, we should use scientific computing libraries to solve this issue but that would slow down computations and will require a lot of change in the codebase. This is probably not feasible for the gain in accuracy and is probably the reason why both kstars and siril doesn't use those libraries.
Thanks and Regards
>> the results of statistic, particulary sigma, of the frame is very different from the three others software: Iris, Pix, Siril as you can see on the joined images. Why ?
I just took a glance in the statistics functions of siril and kstars. The algorithms used seem a bit different to me, however I think using functions like sqrt(), division etc.. are bound to cause inaccuracies with floating point numbers.
This link gives an insight about what those inaccuracies could be. So this inaccuracy in each stage of computation may or may not get exaggerated, and this exaggeration will be different for different algorithms. Sometimes choosing to do some mathematical operations before or after a stage in the same algorithm may work out on paper but not on computers.
I'd love Jasem's take on this too.
>> - the way the square must be set on the image is not very convenient. It's best to draw the frame on the image at the desired location and size. As all the other software do: Pix, Siril, Iris
Drawing the frame is possible with shift+click if thats what you are looking for. However if you want to specify x,y and size for the square thats a new thing
Ok, Im going with a tooltip which shows sigma and median.
Sorry I wasn't able to find time lately. Let me know whether I should output the details in
1. an overlay on top of the image itself ( although limited number of stats, like Width x Height, sigma as this looks messy )
2. a new floating window with the same stats table (similar experience as in Siril )
3. the existing stats panel itself (which alternates between full image stats to selection stats depending on a button )
Attached Image shows how it would look in option 3.