Master flat is over...
 
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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.

Master flat is over correcting

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(@skestergmail-com)
Main Sequence Star
Joined: 8 years ago
Posts: 23
Topic starter  

I'm having trouble with calibration on the data I captured last night.  I created a master flat, that was calibrated with a master dark, master bias, and bad pixel map.  I then calibrated the lights with all of the above masters.

However, when I view one of the lights  in linear-calibrated mode, the master flat is over correcting the image.  The same is true for the final integration of the lights.  Instead of correcting the vignetting and dust motes, the corners and dust motes go from being darker than the rest of the image, to much lighter than the rest of the image.  It's as if the master flat is being applied more than once.

One thing to note.  The lights were captured via Sequence Generator Pro, and were stored as fits files on the laptop.  The darks, flats and bias frames were capture on camera in Nikon RAW (NEF) format.

Any idea what I am doing wrong here?  Thanks



   
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(@skestergmail-com)
Main Sequence Star
Joined: 8 years ago
Posts: 23
Topic starter  

Replying to my own original post.  I had a suspicion that the issue was related to the lights having been taken with SGP and stored on the laptop in .FITS format, while the flats were stored as Nikon .NEF files on the SD card.  To test this theory I converted the flats from NEF format to FITS format before loading them into APP.  I then calibrated the new .FITS flats with the same MB, MD and BMP as before, and generated a new master flat. 

I then calibrated the lights with the MB, MD, BPM and new MF.  The calibration now looks correct, with the flats removing the vignetting and dust mots.  It is now clear to me that the original issue was somehow caused by the flat files being loaded as .NEF while the lights were loaded as .fits.

This would seem to me to be a bug in APP.  I am using version 1.0.68.

Thanks,

Scott

 



   
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(@Anonymous 174)
Joined: 9 years ago
Posts: 5702
 

Hi Scott,

Thanks for your own research into this! That is indeed very interesting. I'll let Mabula know (@mabula-admin), he should be here tomorrow.



   
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(@astrogee)
Black Hole
Joined: 8 years ago
Posts: 244
 

Yes, I'm getting this problem in general with version 1.0.70 - but not solved. I've used data from a Canon 6D (CR2 files - flats and lights) and SBIG camera (fits files - flats and lights). Attached is an example of the SBIG mono camera. I used only 5 luminance lights and 5 luminance flats:

Screen Shot 2018 12 31 at 1.19.22 PM
Screen Shot 2018 12 31 at 1.19.37 PM

I put the files in this dropbox folder: 

Dropbox Logo Dropbox File (Private or Invalid)

Thanks

Greg



   
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(@astrogee)
Black Hole
Joined: 8 years ago
Posts: 244
 

Well this is a bit of a surprise but I added bias frames and now the calibrated frames are flat. Looks good.

Screen Shot 2018 12 31 at 6.28.28 PM


   
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(@Anonymous 174)
Joined: 9 years ago
Posts: 5702
 

Could it be you didn't use bias frames while making the masterflat?



   
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(@astrogee)
Black Hole
Joined: 8 years ago
Posts: 244
 
Posted by: Vincent Groenewold - Moderator

Could it be you didn't use bias frames while making the masterflat?

Hi Vincent, thanks for your reply.

Yes, that seems to be the issue. I made the mistake of trying to use a master bias that was generated by another program but that didnt work at all. So I tried without bias and didnt realize it would affect the master flat as much as it did. Finally I regenerated the master bias and master flat with the original bias frames and I'm getting very nice results now.



   
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(@Anonymous 174)
Joined: 9 years ago
Posts: 5702
 

Indeed the best workflow in APP is to always use raw data, not touched by any other processor, to go forward. APP uses the entire sensor data which many other programs don't do as they use dcraw to convert the data. This causes the dimensions not to be the same and it fails on that. There's a lot of statistics at play when using calibration data and for that to work correctly, a masterflat needs to be bias and dark-signal free as much as possible (I always use bias, darks and a BPM to correct them). If those signals are still there it'll cause APP to make a wrong estimation of the gradient-signal in the lights.



   
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