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.
The bias pedestal is an ADU (Analog Digital Unit) offset in your data. This pedestal is always there, in your light, flat, dark and bias frames. So the ADU values up until this offset value is always there and it actually is not real data. All ADU values above the bias pedestal are real data, but should be interpreted as the ADU value minus the Bias pedestal.
Let's look at a master bias frame of a zwo optical asi1600mm-cool camera and it's histogram:
 The histogram shows you the value of the bias pedestal. It's almost exactly located at the peak of the histogram. Try to know this value for your camera's sensor with the ISO/gain and /or offset that you are shooting with.
- For DSLR camera's this value normally is the same for all ISO settings.
- For users of astronomical CCD/CMOS camera's, the bias pedestal corresponds to the offset and, usually, can be set manually depending on the camera's manufacturer.
In the FITS header of the master bias, created by APP, you'll find the ADU value of the bias pedestal, in this case we see:
HDU1 - CALFRAME= 'master bias'       / master bias frame                            Â
HDU1 - INSTRUME= 'ASI Camera (1)'    / instrument name                              Â
HDU1 - CFAIMAGE= 'no     '          / Color Filter Array pattern                   Â
HDU1 - MEAN   = ' 1,53E+02'         / mean of channel                              Â
HDU1 - MED    = ' 1,53E+02'         / median of channel                            Â
HDU1 - SIGMA  = ' 3,12E+00'         / standard deviation of channel                Â
HDU1 - NOISE  = ' 2,93E+00'         / MRS gaussian noise estimate of channel   Â
The median/mean values indicate it: 1,53E+02, which is a scientific notation for 153 ADUs.
To come back to:
 "So the ADU values up until this offset value is always there and it actually is not real data."
This is the fundamental reason, why this bias pedestal is so important to understand.
In light frame calibration this bias pedestal must be subtracted by either
- a Master Bias of the same ISO or gain + offset
- A Master Darks of the same ISO or gain + offset.
- Or a Master Dark of MasterBias subtracted darks + a Master Bias. both of the same ISO or gain + offset.
APP, currently, will not allow the use of a MasterBias shot with a different ISO or gain+offset than the ISO or gain+offset of your lights, since this will lead to suboptimal calibration for the read noise patterns of your sensor.
For flat frame calibration the same holds, flats need to be calibrated using:
- a Master Bias of the same ISO or gain + offset
- A Master Dark of the same ISO or gain + offset.
- Or a Master Dark of MasterBias subtracted darks + a Master Bias, both of the same ISO or gain + offset.
