2026-10-09 APP 2.0.0-beta48 has been released !
This is mainly a bug fix release for the reported bugs in beta47. In addition it has a significant User Interface performance improvement noticable when you need to process 1000s of images in APP.
2026-10-03 APP 2.0.0-beta47 has been released !
This is a very big release... many code optimizations/rewrites, many parts of APP are much faster and more precise, especially star analysis and registration are much faster ! Big mosaics will go much faster 🙂
And we introduce a new preview filter, which includes the new Adaptive Deep Sky Stretch and a General Levels Stretch, this has been long over due. The old preview filter (the panel on the right side to stretch and preview your data) has not been updated for a couple of years and it is a critical part of any APP session.
Adaptive Deep Sky Stretch or ADSS is a much more intuitive stretch algorithm. It is also color preserving (which is a great new addition in itself ! ) which means that the highlights are no longer bleached, color is maintained from the linear data while stretching. You can simply stretch your data using the sky background level and signal width sliders which work much easier and more intuitive. You no longer need to fiddle with the old complicated sliders with zoom buttons. All the zoom buttons for the sliders are made redundant. And you can enter slider values in the slider value fields yourself. I will make a youtube video in the coming days to explain and fully introduce ADSS. Once the video is ready, it will be highlighted on the forum.
RGB Combine upgrade !. The RGB Combine Tool has been rewritten mostly. The tool is faster and easier to use and most importantly, the Luminance slider to inject a luminance channel or channels into the RGB composite is now working correctly. It no longer bleaches the RGB colors. Combined with the new ADSS preview, you will get much better and easier great composites with great color! I will also explain this in a new youtube video.
Hello
When you do a star analyse you get FWHM min, max and shape.
What is the shape related to?
I am sure it is not related to the roundness of the stars, in fact, the frame that APP use as the reference (FWHM min and max very similar) has the greatest value of FWHM shape, so what is this?
Regards
Jose
Hi Jose @skysurvey,
Thank you for your question.
The FHWM shape is the combination of both star size and roundness.
I use the following formula:
star shape = roundness * size
where roundness and size are formulated in a way that better is higher:
roundness = minFHWM/maxFWHMÂ Â ( so perfect circulair stars have roundness = 1, otherwise the roundness score is lower)
size = 3 / (( minFWHM + maxFWHM)/2) ( so smaller stars have higher size score)
The minFWHM and maxFWHM are calculated per star since they are all fited with 3D intensity profiles.
The value of minFWHM and maxFWHM for the whole image is the median value of all stars that were analysed in the image, giving you a star shape score for the whole image.
And the higher the star shape score, the smaller and rounder your stars are.
I use a general 2D gaussian model to fit all stars to in which I find sigmaX, sigmaY, and rotation angle theta and the model has the shape as shown in this image from one of my presentations:
The A,B,C contain the sigmaX, sigmaY and theta.
Let me know if this is clear.
Mabula
Yes!!! It is clear now.
Let me tell you that your brain must be like the Rosetta Stone, I could have been thinking for years trying to know the exact formula without succeeding, but I completely understand the idea, and it works, look at my numbers of a Ceres photograph taken from the middle of Madrid:
Â
So, talking about the best frame (the one used for reference), Min FWHM=1,55, Max FWHM=1,62, and when I apply the formula:
FWHM shape = (6*(Min/MAX))/(Min+Max)= (6*(1,55/1,62))/(1,55+1,62)=1,81 that is the number that appears in the correspondent column of APP, and it is clear, the higher the number the better the star is (better roundness and lower size).
Thank you very much Mabula, I love APP 😉
Regards
Jose
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Excellent and thank you Jose 🙂 !
You are most welcome !
Mabula
Hi Susan @safinsd,
As you can see from your uploaded image, eccentricity is not a very intuitive measure of star roundness due to it's non-linear behaviour.
The formula for eccentricity can be found here: https://www.cuemath.com/geometry/eccentricity-of-ellipse/
Â
(1 - b^2/a^2)^0.5
using minFWHM and maxFWHM then the eccentricity formula becomes:
(1 - minFWHM ^2/maxFWHM ^2)^0.5
Â
The Astro Pixel Processor star shape value of 0,8 is more than only star roundness, so you can not compare it directly.
As indicated above, star shape contains both star roundness and star size:
star shape = roundness * size
where roundness and size are formulated in a way that better is higher:
roundness = minFHWM/maxFWHMÂ Â ( so perfect circulair stars have roundness = 1, otherwise the roundness score is lower)
size = 3 / (( minFWHM + maxFWHM)/2) ( so smaller stars have higher size score)
Â
Now in aswer to your question:
Let us assume that size = 1 (meaning the stars have roughly a FWHM of 3 pixels)
Then star shape = 0.8Â means star roundness = 0.8 which then means that minFWHM/maxFWHM = 0.8
entering this in eccentricity formula gives:
Â
minFWHM^2/maxFWHM^2 becomes 0,64
1-0,64 = 0,36
the square root of 0,36 = 0.6
So for stars with FWHM = 3, the star shape = 0.8 gives eccentricity of 0.6.
Please let me know if this is clear.
The Astro Pixel Processor star shape formula containing both roundness and size enables you to directly compare all images to be processed for star size +Â roundness combined.
Thank you, Mabula. You are far more advanced than me (of course.) I want to prioritize star shape in my subs and had been removing subs with star shape and quality below 0.8 (was assuming star shape of .8 referred to eccenticity), but don't really understand the implications.
Im confused at were does the 6 come from ? Â I saw the formula in an earlier post that mention's using 3, so I'm kinda confused and must be missing somethingYes!!! It is clear now.
Let me tell you that your brain must be like the Rosetta Stone, I could have been thinking for years trying to know the exact formula without succeeding, but I completely understand the idea, and it works, look at my numbers of a Ceres photograph taken from the middle of Madrid:
Â
So, talking about the best frame (the one used for reference), Min FWHM=1,55, Max FWHM=1,62, and when I apply the formula:
FWHM shape = (6*(Min/MAX))/(Min+Max)= (6*(1,55/1,62))/(1,55+1,62)=1,81 that is the number that appears in the correspondent column of APP, and it is clear, the higher the number the better the star is (better roundness and lower size).
Thank you very much Mabula, I love APP 😉
Regards
Jose
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Thanks
Zach
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If I may be so bold, take a look at Mabula's earlier definition for size, i.e:
size = 3 / (( minFWHM + maxFWHM)/2)
: which is equivalent to:
size = 6 / ( minFWHM + maxFWHM)
Â
Im confused at were does the 6 come from ? Â I saw the formula in an earlier post that mention's using 3, so I'm kinda confused and must be missing somethingYes!!! It is clear now.
Let me tell you that your brain must be like the Rosetta Stone, I could have been thinking for years trying to know the exact formula without succeeding, but I completely understand the idea, and it works, look at my numbers of a Ceres photograph taken from the middle of Madrid:
Â
So, talking about the best frame (the one used for reference), Min FWHM=1,55, Max FWHM=1,62, and when I apply the formula:
FWHM shape = (6*(Min/MAX))/(Min+Max)= (6*(1,55/1,62))/(1,55+1,62)=1,81 that is the number that appears in the correspondent column of APP, and it is clear, the higher the number the better the star is (better roundness and lower size).
Thank you very much Mabula, I love APP 😉
Regards
Jose
Â
Â
Â
Thanks
Zach
Â
Like @mestutters indicates 😉
If I may be so bold, take a look at Mabula's earlier definition for size, i.e:
size = 3 / (( minFWHM + maxFWHM)/2)
: which is equivalent to:
size = 6 / ( minFWHM + maxFWHM)
Â
