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--- blog:photography:night:2021_10_25 [2021/10/30 21:41] – [Images] john
+++ blog:photography:night:2021_10_25 [2021/10/30 22:13] – [Image Processing Notes] john
@@ Line 33: / Line 33: @@
+==== Image Processing Notes ====
+Since this was my first time stacking and processing multiple images, it took a while until I found a solution that **(a)** worked properly on Linux, **(b)** I was comfortable with and **(c)**, was happy with the output from.
+First I tried [[https://siril.org/|Siril]], but I just couldn't get to grips with the interface - I found it entirely unintuitive **and** the tutorial to stack your images just would not run - throwing an error about a line in the pre-processing script which made no sense.
+Then I tried [[http://deepskystacker.free.fr/english/index.html|DeepSkyStacker]] which, although Windows only, seemed to load and run via //Wine//, but ended up crashing repeatedly when processing images.
+Eventually I looked at [[https://www.hnsky.org/astap.htm|ASTAP]] which did everything I wanted and was clearly laid out.
+I tried loading images into the applications as the came from the camera, but all of my results were over-exposed, suffering varying levels of optical aberrations and just generally didn't look particularly great - even though stacking brought out far more detail than I had seen before.
+Eventually I settled on the following routine (which works well for me, in my fairly light-polluted garden):
+**1. Load RAW files into Rawtherapee and adjust as below**
+{{:blog:photography:night:2021_10_25:rawtherapee-initial-exposure-settings.png?300|}} {{:blog:photography:night:2021_10_25:rawtherapee-initial-chromatic.png?300|}}
+//The chromatic aberration settings are likely particular to my lens which is of course in this case is the ultra-wide 11mm Tokina. At 11mm and f/2.8 it has quite bad chroma in the corners of the image. It would likely not need such aggressive settings stopped down, or at the other end of it's focal length (16mm).//
+**2. Save as TIFF, 16bit. Load into GIMP and apply gradient as below in the direction of any light pollution**
+{{:blog:photography:night:gimp-gradient-settings.png?200|}} {{:blog:photography:night:gimp-applying-gradient.png?600|}}
+//Depending on the level of light pollution, increase/decrease the opacity of the gradient, as well as the length it is applied to.//
+**3. Load all of the processed TIFF files into ASTAP as your light files. There will be some warnings about missing metadata, but this doesn't appear to impact the final image.**
+**4. Let ASTAP do the stacking, along with any dark, flat and bias images.**
+{{:blog:photography:night:astap-stacking-settings.png?600|}}
+//For me, the best results were with the AstroSimple option and Sigma Clip stacking options as above.//
+**5. In the resulting stacked image, if the star colours look //off//, try another stacking/colour de-mosaic algorithm, or try the 'Autocorrect image colours' option from the tools menu.**
+**6. Export as TIFF from ASTAP and load back into your image editor of choice. I used Rawtherapee to do final image/colour enhancements; playing with the colour and black/white highlight balance.**
+{{:blog:photography:night:rawtherapee-final.png?600|}}