Masked stretch

[EG1]

Hi, I am a new star tools user…

The program is fantastic, and many elements such as noise control are incredible.

However, I do miss certain elements from pixinsight.

In particular, I find the pixinsight masked stretch function to be superior for certain situations, such as globular clusters.

Please implement an equivalent.

Thank you, Eric

[admin]

Hi Eric,

Thank you for this feature request.

Masked stretching is a very crude tool that really has no place in any modern image processing software.
It has the potential to introduces artifacts, but most most of all, it is sub-optimal.

Non-linear stretching in StarTools by means of AutoDev (please note FilmDev should not be used unless you wish to emulate film!) serves a very specific purpose. From the AutoDev docs;

Keeping in mind AutoDev's purpose
The purpose of AutoDev is to give you the most optimal global starting point, ready for enhancement and refinement with modules on a more local level. Always keep in the back of your mind that you can use local detail restoration modules such as the Contrast, HDR and Sharp modules to locally bring out detail. Astrophotography deals with enormous differences in brightness; many objects are their own light source and can range from incredibly bright to incredibly dim. Most astrophotographers strive to show as many interesting astronomical details as possible. StarTools offers you various tools that put you in absolute, objective control over managing these enormous differences in brightness, to the benefit of your viewers.

E.g. StarTools' "do-it-once-do-it-right" mantra sees you gradually refine your image (the suggested workflow is no accident - it progresses from coarse to fine detail enhancement), much like a sculptor progresses from coarse block of marble to an intricately detailed sculpture. First order of business is to establish a stretch that is as neutral as possible and does not pick "winners" in the shadows, midtones, nor highlights. This is you coarse block of marble. Masked stretch (or levels and curves, etc.) is not concerned with this notion at all, and would you start off with a Masked Stretch image, you would have a harder time wielding the tools that are supposed to build on your "base".

Or, taking an globular cluster as an example, you would find a stretch with AutoDev, that is the best compromise between showing the entirety of the cluster (including its fainter stars in periphery) and resolving (probably only just) the core. You then progress - to taste - resolving the core with the Contrast module (medium-to-large local dynamic range optimization) and - most useful for globs, the HDR module (medium-to-small local dynamic range optimization; vary Detail Size Range if needed), You finish off with deconvolution, which will gladly use the "helpful" dynamic range allocation to reolve the finest details.

All the steps that came after AutoDev will have achieved better results thanks to AutoDev's inital neutral dynamic range allocation. It means these tools don't have to work harder than absolutely needed to bring detail back from the brink. The latter is the crux of the matter and why tools like Masked Stretch or levels & curves etc. are considered sub-optimal and best avoided.

All that said, if you have a dataset where the use of MaskedStretch yielded a significantly better end result, please feel free to share the dataset and the result itself. I am always looking to improve StarTools or better cater to edge cases, in the case these are not covered.