Wednesday, 24 November 2010
I find Photoshop Actions extremely useful while processing astro-images. Noel Carboni's Astronomy Tools are a wonderful set. Rather than rewriting actions that do the same thing, my idea is to supplement them.
Shamelessly titled "Troy's Astro Actions", here is a list of each action and what it does. Each is non-destructive, ie will not alter the starting image. Just highlight the layer you want to apply the action on. It can't be an adjustment layer. Oh yeah, they're free as in beer.
Threshold Crop: After stacking there is inevitably some mess around the edges from where each frame didn't quite line up with the others. I found using threshold a convenient way to highlight where these misalignments are for cropping. When running the action it will pause to allow you to adjust the threshold. Use the slider to find a point where the misalignments are clear, then click OK.
Next a crop window will appear for you to adjust, then click Enter.
BIG S T R E T C H: I use this curves adjustment when the histogram needs a lot of stretching from the dark end. The action merges as a layer on top. If it's too much of a stretch, just manually adjust the curves or delete the adjustment layer.
Small Stretch: Similar to the big stretch, but smaller. More subtle.
Separate Stars and Sky: Removes the stars in one layer called "starless", and puts the stars into another layer called "stars". I'm very proud of the clever layer naming system adopted. The stars layer will be mostly black and the stars, and the layer blending mode will be linear dodge (add). I've found that to give the best results. I have written a more detailed post on this action and will be posting it soon.
Just Remove the Stars: Similar to the above, but doesn't add the stars layer.
Median Noise Filter: This is a very quick and simple, not perfect, noise reduction action. It doesn't treat chromatic noise, just lightens dark pixels.
Grain Reduction: This is a modified version of the technique explained in R. Scott Ireland's excellent book "Photoshop Astronomy". After using this action, might be best to adjust the opacity down a little.
Download Troy's Astro Actions v0.9.2 last updated 4/12/10