Processing night images

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This section is mainly to add notes and information that relates to processing of images.

A. Deep Sky

        Start with PixInsight

  • To start I use PixInsight to stack the frames. It is necessary to have bias, dark and flat frames at the ready. The flats wizard in SGP is good for getting the flats exposure right. I find a cloudy sky with several layers of quality tracing paper and two layers of white T shirt material stretched over a frame does well. Having used PixInsight once with many bias, dark and flat frames, masters are created which can be used until such time it is necessary to make new flats.
  • At the moment I make it simple and use the WeightedBatchProcessing script for each of the LRGB sets of frames. Then use the star alignment tool to align these four separate images using the L as the reference image. If the RGB have been binned 2×2 this then doubles the pixel size so it matches the L.
  • I tend to do some processing in PixInsight using the histogram tool but don’t worry about anything remotely final. I make sure the RGB channels are processed equally. Save all channels as tif.
  • I know PixInsight is probably capable of carrying on to get a better job, but have not yet mastered its intricacies, so from here on I switch to photoshop.

      Create LRGB in Photoshop

  • Using levels and curves I get reasonably bright RGB images, not worrying if there is a bit of noise when processing faint objects. Then CTRL A + CTRL C on one of them and with New make an RGB file the size of the clipboard. Make the channels tab visible and the CTRL A + CTRL C and past the R,G and B images into the appropriate channels.
  • Make a new layer positioned at the top and make this a luminosity layer. The luminosity image is processed with more care to be a clear and free from noise as possible. Use levels, curves and AstroFlats Pro. When satisfied CTRL A + CTRL C and paste this in the luminosity layer. Save as a psd file for something to go back to if bungles.
  • Now it is case of using the colour balance, vibrance, shadows/highlights and any other tools that may seem relevant in Photoshop to pull out the best image. In items such as the great nebula in Orion I found that using highlights to reduce the excessively bright white areas was better than using two exposures and layer masking.  Often this is a matter of personal preference!
  • More on PixInsight in this processing in due course!

Other Wrinkles 

 1. Printing

  • To print is is necessary to brighten the image by sometimes as much as 25% even if this looks excessive on screen.

2. To print to A4 from Trius 35 full frame.

  • Crop the picture slightly from 4008 to 3979 in width.
  • Print to the Canon and set it to be “borderless”.
  • Set the scale to give 277mm x 186mm – this will need a scale of about 19.8%
  • When printed this will leave a slight border so it fits in a frame with an A4 mount without losing any edge.

3. To use curves on part of a frame if some areas too near saturation.

  • Lasso the area you what to do further work on so leaving behind the bits already OK. Use about 15px feather, but maybe different in varying circumstances.
  • Create a new Curves adjustment layer by clicking on the split circle icon and selecting curves from the sub menu that appears.
  • The curve for amending the area selected will then appear in the properties window.
  • It may need a bit of the clone too to smudge the final image so the transition is smooth and not noticeable.
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B. Lunar Images

  • I have found AutoStakkert3 to be better than Registax for stacking – it works well and does not crash. I do not use the sharpening tool as AS3 says itself this is only to give an indication.
  • For sharpening, I found ImPPG.exe (which has an icon f*g) to be really good. It is possible to adjust the simple parameters to get good sharp images which don’t look overdone.
  • These two programs also work extremely well for the sun, which limits the learning curve.
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