Masked stretch in Dev?

Questions and answers about processing in StarTools and how to accomplish certain tasks.

Masked stretch in Dev?

Postby jimmy101 » Wed Apr 17, 2019 1:23 am

Hi All.. first post!
I've being using ST for some time now but one thing that would be very handy to do is a masked stretch, in particular to reduce star bloat (particularly on my RASA that sucks in starlight!). All my images look good and I use shrink/tighten on stars but is there a way to reduce star bloat when using dev (apart from obviously stretching less)? Currently I just create two stretches and overlay them later in GIMP and it works OK but it would be nice to do once in Dev. Maybe this could be a feature request...
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Re: Masked stretch in Dev?

Postby admin » Mon Apr 22, 2019 1:37 am

Hi,

Thanks for posting!
If Develop or AutoDev doen't yield the results you're looking for (they should mitigate star bloat quite well though!), you can easily do a masked stretch by using the Layer module;

  • Do a regular stretch to taste, focusing on the shadows and mid tones.
  • Go into the Layer module
  • Click Undo -> background
  • Select "Where fg is light use bg" for "Brightness Mask Mode".
  • Tweak Brightness Mask Power to taste

Hope this helps!
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Re: Masked stretch in Dev?

Postby Rkonrad » Mon Apr 22, 2019 5:21 am

Ok..so this works but we get waning messages about using that module while tracking is engaged. That is ok? Wouldl this have any impact in the noise reduction in the end? Ivo, you had also advised something similar about bringing the stars down in the Heart Nebula I was working on. Should this all be done after tracking is complete. It just seems logical to ask this considering what I understand so far about the tracking process. Thanks.

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Re: Masked stretch in Dev?

Postby admin » Tue Apr 23, 2019 9:53 am

Rkonrad wrote:Ok..so this works but we get waning messages about using that module while tracking is engaged. That is ok?

Good question/point! It is indeed important to be careful when using the Layer module mid-Tracking. Some operations will interfere with Tracking's ability to evaluate how noise propagation changes between operations/modules. The masked stretching, applied in this matter does not however.
Would this have any impact in the noise reduction in the end? Ivo, you had also advised something similar about bringing the stars down in the Heart Nebula I was working on. Should this all be done after tracking is complete. It just seems logical to ask this considering what I understand so far about the tracking process. Thanks.

That procedure is best applied after Tracking, yes.

Rule of thumb for can I / can't I do this within the Layer module while tracking is on, is; you can if the pixel change can be expressed as a simple transformation of the source pixel at that same location (for example a multiplication, addition, exponentiation). An operation should ideally not be dependent on neighboring pixels and should not be applied selectively, or as a function of a threshold.
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Re: Masked stretch in Dev?

Postby jimmy101 » Sat May 11, 2019 4:20 am

Thanks Ivo!
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