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9, Post processingSiril has developed a lot and now with version 1.4.0 I do some of the Post processing in Siril and only do the final touch in Gimp. Here are VeraLux HyperMetric Stretch, StarNet and GraXpert. Post processing or maybe you should say between Pre processing and Post processing. Siril version 1.4.0 VeraLux HyperMetric Stretch:VeraLux is a HyperMetric Stretch Phyton script for Siril. 
To use it it must be enabled in Siril. Go to the preference menu. 
Under the Script menu, scroll down to VeraLux ... and enable it. 
After it's enabled you can start it from the Siril's Python Scripts menu. First open the dark and flat calibrated, stacked and color calibrated image you want to process. It should be in linear mode. The green blob is Andromeda M31 galaxy in linear mode, barely visible. 
This menu pop up and from here you control VeraLux's function. Choose your camera profile, use the default settings and it will in most cases be good. Click on "Auto-Calc Log D" button and it will setup the parameters. This is the version 1.3.0. 
There is a Live Preview that you can activate. I missed the color calibration in the earlier step, but otherwise okay. Earlier this took me 15 to 45 minutes to do with Gimp. In VeraLux it took less than a minute and it looks much better. 
The result from VeraLux, it can be fine adjusted in Siril's Tools, Stretch, Curves. Easy to do in Siril, or it can be done in Gimp with a lot of more work but with better control. 
Another example of image processing on a nebula, this done in Gimp. It took me at least 30 minutes to achieve this. 
Same image but now the image processing is done with VeraLux, a two click work. Much better contrast and color, no extra processing done. 
VeraLux make a lot of details to stand out in the famous Horse Head nebula. The photo is taken with a Pentax 645 300 mm f/4 lens and a Nikon D800 full frame camera. 
Even the weak nebulosity around the hot stars in M45 Pleiades came out without increasing the noise. With these promising results I will use VeraLux a lot more in the future. Until then I have to learn how to get the best out of it. VeraLux HyperMetric Stretch tutorials:
StarNet:The main purpose with StarNet is to remove the stars, from a nebula or similar object. Without stars it's easier to process the weak signal from the nebula. Afterwards the stars can be inserted again. StarNet must be downloaded and store somewhere on your computer, scroll down the StarNet page and you find downloads at bottom. 
When downloading and placed in a library is done Siril must be setup, open the Preferences menu. 
Open Miscellaneous menu. Navigate to the library where you installed StarNet and click on StarNet++.exe. Then click Apply. 
StarNet can after the installation be found in Siril's Image Processing menu. 
Andromeda Galaxy processed with StarNet. The stars are gone but leave the satellite galaxies to Andromeda. From this much heavier image processing can be done on the galaxy. When doing this in Gimp it's very difficult to get this good result. This is also a tool I will use more in the future instead of the manual method I have used in Gimp. StarNet tutorials / informations:
GraXpert:Removing background from astroimages can be a challenge, especially if they are taken from a light polluted place. That's when you can use GraXpert. Graxpert can be run from inside of Siril or as standalone, it's the same installation. You can follow this tutorial which explain how to do the installation and setup: Using Graxpert in Siril. One thing to make clearer, the Windows library AppData that they talk about isn't so easy to find, it's hidden. You hade to change the Windows files setup to make it visible. 
A typical example how my images look like, heavy light pollution make them difficult to flat calibrate to some higher degree. This is a stacked image of M81 and M82, it's sub flats are calibrated, 1 degree dark subtraction, aligned and stacked. And a mild stretch to make the problem visible. And last the image is cropped to get rid of the uneven edges, this is important. 
With Graxpert most of the uneven background is removed. I prefer to run Graxpert direct, I have more control over it then. I used the RBF function. It's possible to denoise the image too, but take powerful computer, my I7 16GB ram machine take forever to do it. I have a new one going on, a Ryzen 9 with 32GB ram, I hope that one handle this better. The camera is a Nikon D800 with a 36 Mpix sensor. 
Central area of the image, better than what I have achieved earlier. You can find the uncropped version of the image here and more info about it: M82. 
Another object and how the sensor points are placed. Similar to Siril but they adjust by automatic to avoid stars, much easier. Around the galaxy I have manually taken away the sensor points. I placed groups of extra sensor points where the gradients are high. 
The background Graxpert calculated and this will be subtracted from the image. GraXpert tutorials / informations:
Coming more info soon, I haven't test it yet. A lot of tools to play around with as an alternative to do it manually in Gimp or some other software.
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