Unexpected result when working on separated background layer

Bugs, glitches and unexpected behaviour.

Unexpected result when working on separated background layer

Postby almcl » Tue Aug 29, 2017 7:01 pm

Not sure if this is a bug, or something I am doing wrong, but when separating stars from the background by use of the heal and layer modules http://forum.startools.org/viewtopic.php?f=7&t=244 I've started getting a rather unexpected result.

The original saved background image looks like this in my latest example:
original separated background.jpg
original separated background.jpg (77.21 KiB) Viewed 89 times


But if I try to reload it, or open it in the develop module it appears as though a further stretch is being applied:
what happens when it is reloaded.jpg
what happens when it is reloaded.jpg (102.64 KiB) Viewed 89 times


This is rather the reverse of what I want to do as I am seeking to 'tone down' the rather noisy background and tune out some of the star bloat.

Don't think this has always been so, but not sure when it started happening.

System is StarTools 1.4.327 on Win 7 64 bit pro
Skywatcher 200P with an astro modded Canon 700d, cls ccd filter, field flattener, guided by QHY 5Lm, PHD2
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Re: Unexpected result when working on separated background l

Postby admin » Fri Sep 01, 2017 12:15 am

Hi,

What appears to happen is that the image is being normalised; the dynamic range is re-distributed so that the brightest pixel in the original is now pure white. This is normal behaviour in the Develop module, because... well... global dynamic range optimisation is its job! :)

Just reloading should not trigger this behaviour though, unless you reload in the Layer Module while having "Cap Mode" set to "Normalize"?

If you really need to crunch down the dynamic range again, then you can use the Layer module's "Multiply Foreground" Layer Mode. What this does is use the "Blend Amount" as a simple multiplier for all pixels. E.g. if you want all pixels to be just 50% as bright, set the Blend Amount to 50%.

Does this help?
Ivo Jager
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Re: Unexpected result when working on separated background l

Postby almcl » Sat Sep 02, 2017 8:58 pm

Thanks for that, Ivo. The tip about correcting it in the layer module is particularly welcome - I always felt using the gamma wasn't the best way to proceed.

But to the point in your second paragraph, a simple reload definitely does trigger a further normalisation without any other intervention. Could this be something in my set-up?
Skywatcher 200P with an astro modded Canon 700d, cls ccd filter, field flattener, guided by QHY 5Lm, PHD2
almcl
 
Posts: 72
Joined: Wed Jan 21, 2015 7:15 pm
Location: Shropshire. UK

Re: Unexpected result when working on separated background l

Postby admin » Sun Sep 03, 2017 1:51 am

almcl wrote:But to the point in your second paragraph, a simple reload definitely does trigger a further normalisation without any other intervention. Could this be something in my set-up?


Hmmm... You're right! It does it with loading TIFFs (i loaded a PNG when testing).
Will fix for 1.4.329. Thanks!
Ivo Jager
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