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.
When I use the RGB Combine tool, for LRGB its treats L as a white layer of 4 layers, forcing the result to white. This is not correct. L is the intensity to which you take the RGB intensity, ... you compute the amount R contributes (say 23%) to a particular pixel, then multiply that times the L amount to get the new intensity for R, etc. Each color is painted onto L proportionately.  The results should not be White but boosted colors, based on their proportion to each other multiplied by the Luminance level, give it an even strong intensity than it would have had without the L. Its completely not working as is, since its treating a 4 (LRGB) as equal layers.  For example let's say your Luminance is 200 for a pixel, and you compute the RGB (based on RGB not LRGB) percentages for that pixel based on your data, let say that comes 37%/44%/19% (you throw away the old RGB intensity from the individual files and replace it with the intensity you compute here), so then you would end up with 200x.37 = 74 RED, 200x .44 = 88 GREEN, and 200 x .19 = 38 BLUE.  Instead you're just giving us white.  Its not about moving the slider down so white is not there revealing the color its about recomputing the intensity of each pixel based on L values as percentage of RGB, its a new intensity. Â
For example, here is APP on the LEFT;  and ASIStudio on RIGHT (same FITS files as input). Yes I pushed recalc after selecting files on APP using LRGB formula.Â
Skye (@skysong)
I believe you are right about this. I tend not to notice the issue as I typically process luminance separately and combine it in Gimp as the last step. Now that I think about it I am a bit surprised it hasn't been raised more often.
JC
@connor231 Oh I'm a GIMP user too, how do you do your technique? They fact that we get white/ gray with LRGB, then reduce L to low levels (basically to remove it back to RGB) proves the current algorithm is not working. The color should be "boosted" by the L proportionately, but instead L is added in as white layer, which is wrong.
Skye (@skysong)
If you are asking about the final combination step - its fairly straightforward.
You load the mono luminance and the rgb image into Gimp as separate images. Copy the luminance, switch to the rgb image and select 'Paste as' 'New Layer in Place'. The layer panel will now show two layers. Select the top one (your mono luminance) and change the layer blend mode from 'Normal' to 'Luminance'.
At this stage you can play with the Opacity of the top layer. You can leave it at 100%, but I sometimes find that reducing it to about 70% can look a bit better. Once you have chosen the opacity, then select the luminance layer and do 'Merge Down' (either in the Layer menu or by right clicking the layer entry) to create a normal flat image.
Lastly, I still find that the saturation sometimes takes a minor hit and I give it a saturation boost.
This is just how I like to do it. There are other methods - some people prefer to switch to LAB colour, swap the luminance, and switch back to rgb.
JC
Skye (@skysong)
If you are asking about the final combination step - its fairly straightforward.
You load the mono luminance and the rgb image into Gimp as separate images. Copy the luminance, switch to the rgb image and select 'Paste as' 'New Layer in Place'. The layer panel will now show two layers. Select the top one (your mono luminance) and change the layer blend mode from 'Normal' to 'Luminance'.
At this stage you can play with the Opacity of the top layer. You can leave it at 100%, but I sometimes find that reducing it to about 70% can look a bit better. Once you have chosen the opacity, then select the luminance layer and do 'Merge Down' (either in the Layer menu or by right clicking the layer entry) to create a normal flat image.
Lastly, I still find that the saturation sometimes takes a minor hit and I give it a saturation boost.
This is just how I like to do it. There are other methods - some people prefer to switch to LAB colour, swap the luminance, and switch back to rgb.
JC
Yeah i saw there is a way to load all 3 colors separately to GIMP, and then the L, as the last layer and flip it to Luminance, but its I'll have to spend some time to learn it. This is probably the best way to to do it in GIMP, but I takes some time to learn it.  Would be even better if APP can update their algorithm.Â
Skye (@skysong)
I didn't suggest loading r, g and b separately to gimp. Just load the rgb combined file (not lrgb) and the mono luminance. Then it can literally be about four clicks and you are done.
JC
Hi Skye @skysong,
When you apply a luminance layer 100% it can seam that the image is whitened. But if you simply enable saturation and/or increase saturation in the preview filter, the colors will be there. Our RGB combine tool works currently with the HSL color model and L is a real L, not a white layer.
I have opened a new issue on my todo list to have a good look at the Luminance calculations to make the RGB composites in the RGB Combine Tool.
I know that this whitening effect is there, so I will definitely try to have this work better going forward 
It is on our todo list, to improve this with a more advanced color model going forward.
Please let me know if this helps,
Mabula
