StarTools

22 x iso200 x 30 secs under Bortle 5 skies preprocessing in Siril. This is a slightly pixelated png screenshot from Siril imported to ST. And while very likely the best focus my gear can do having picked out the stars in the trapezium.

Is there a way to do a logarithm stretch in ST. For this kind of work it would be very useful. A full stretch just obliterates the core. The halos around the bigger stars seem a lost cause. Can't improve on those at all.

Hi,

I'm not entirely sure what you mean by "logarithmic stretch", but indeed all stretches in StarTools' OptiDev and FilmDev are non-linear.

Stretches based on this or that specific mathematical function will never yield optimal or predictable results (in terms of interface). And while global stretching will always be a (necessary) compromise, StarTools' Optidev generates custom linear stretch functions that is based on a region of interest (RoI). This is by far the most useful way of using a global stretch. In this case, for example, you may wish to specify a RoI over the trapezium.

However, in general it is better to choose a stretch that works to show the entire object, and then further tame a bright cores (like that of M42) using local dynamic range manipulation algorithms as found in the Contrast and HDR modules.

Hope that helps!

Thanks Ivo. I have just switched to v1.9 and OptiDev makes all the difference even with the default settings.