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.
How do you use these settings: background, noise, range under the individual colors?
Best way to neutralize green in a OSC image? Thanks
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Mabula goes into the HSL here more, maybe that already helps? https://www.astropixelprocessor.com/community/main-forum/processing-with-narrowband-only-to-get-a-color-image/#post-21291
That link is not really helping me. It seem this is a preset for a range of the color? I don't understand what this means "background + 2*noise - 25% range" or how it works, or how to use it. Carol
Hi,
I hope this is the type of explanation you are looking for.
The HSL selective colour tool provides a means of adjusting the colour values in an image file by:
a) selecting a colour (or the All or a Grey scale options) via the Color selector
b) selecting pixel brightness range using the Range selector tool.
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Mabula has provided several preset options which I assume he feels will be most useful for the average user, but a user has the option to refine the selected values using the sliders below the preset selection.
The presets are arranged by brightness levels, low to high. Thus if you are wanting to modify the very darkest elements of your image then select one of the options:   '0 - background' thru to  '0 - background + 3 * noise'. Read this latter preset expression as 'pixels with a brightness value in the range 0 (ie black) to the background brightness value plus 3 times the noise level value'.
The value of the background level of your subject image is given below the range selector tool. In the image I am currently looking at the (sky) background is 0.00257 on a scale 0 - 1. so very dark areas. I image in monochrome and the noise values for each channel (shown in the FITs headers) are typically less than 0.00005, so very small values but as most images are rather dark, so potentially selecting a large number of image pixels.
Next up are the presets for selecting mid-range pixel values, ranging from   'background - 25% of range'  to 'background + 3 * noise - 75% of range'.  These ranges would typically select the pixels values of, for example, emission or reflection nebulae, or outer regions regions but probably not the very bright cores.
Next, if you are wanting to modify the values of stars and possibly bright galaxy cores, you would select from one of the high value ranges, e.g: '25% of range - 100% of range'  to  '75% of range - 100% of range'.
Lastly, if you say you are wanting to remove an overall colour cast in an image there is the preset: '0% of range - 100% of range', which would select every pixel level having an element of the selected colour. In one of his videos focused on the HSL tool, Mabula gives an example of the use of the 0% - 100% preset for removing Green colour from an image on the basis that Green is only rarely found in astro images.
I suggest the best way to become more familiar with the applicability of the presets is to load an image into the HSL tool then experiment by selecting from the various preset options. By pressing the button 'show colour selection' the image viewer will change to displaying a mask image reflecting the relevant selections. The areas of the image covered by the white areas of the mask will be modified by subsquent use of the calculate button while the black pixels will not.
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Mestutters, thanks you for this explanation. This is what I was looking for.
