Processing color Moon images

The Moon is very tempting and graceful imaging target. It is enough to have some longer focal length instrument without any tracking abilities to capture Moon picture – any dobsonian telescope, SCT or Mak on manual alt-az mount or even larger telephoto lens will do the trick. However single image is usually not enough to reveal color differences across Moon surface. When you stack many of single image frames, then signal to noise ratio and image dynamic range will increase. Then you will be able to raise saturation to see Moon colors.

To achieve this result you will need pictures of Moon (of course) made with DSRL camera or OSC astrocamera. You may start with 10 of them, but more is better. 30-50 frames is good. You will also need two pieces of software:

Stage 1 – PIPP – preparing frames

Images presented in this tutorial were made with Canon 550D camera and 102/714 ED refractor mounted on AZ4 mount without any tracking. These subframes could not be stacked at this point, they needed to be aligned, centred, converted and little bit downsized. In the first step we start PIPP, select our frames in RAW format and we also select option Solar/Lunar Full Disc:

Then in the Input Options tab we select Debayer Raw Image Files, and select VNG algorithm. Additionally I changed color space to Adobe RGB:

Next tab is Processing Options. Here we need to deselect Convert Color to Monochrome and we set Stretch Histogram Whitepoint to 85%. In the Frame Stabilization Mode we select Object/Planetary. We also select Enable Object Detection, and as Minimum Object Size we set for example half of the Moon size in our subframes (in pixels). Next we select Centre Object in Each Frame and depending on Moon phase and orientation we choose one of the options from the drop down (when close to Full Moon we select None). Last thing to do is to set Cropping to the Moon size in pixels plus 100-200px. Then we may click at Test Options button and after a moment we will have a preview window with image generated according to selected options:

If all looks good, then we may progress to Quality Options tab, and then we select Enable Quality Estimations as below:

In Output Options tab we choose format and place to save output files and then in Do Processing tab we start subframes conversion.

Stage 2 – resize

AutoStakkert!2 cannot process images larger than 2000px, so if output images from PIPP are larger, you need to downsize them using any software with this capabilities. My favourite one is Fastone Image Viewer.

Stage 3 – AutoStakkert

We align and stack subframes in AutoStakkert software. We need to select preprocessed image files in explorer window and then drag and drop them to AS! window. We select option Image Stabilization – Surface and Quality Estimator – Gradient and we click Analyze button. After analysis in the window where align points are shown we select AP size and Min Bright. Then we click Place APs in Grid. After a moment Moon image should be covered with align points. Its size and minimum brightness should be adjusted to have no more than 300-400 APs in total. And also they should be placed only on Moon image, not on dark background.

Then in Number of frames to stack we select how many subframes we want to stack. There could be up to four separate values entered, so at the end you will get four stacks and then may compare. In my case I entered here 8, so the software will select best 8 out of total 18 frames. We may also select Sharpened and in Blend RAW field enter 50-80%. Then at the end we will get raw stack, but also second one little bit sharpened already.

Stage 4 – postprocessing

This raw stacked image we may process then in our favourite software (Photoshop, GIMP, etc) to increase local contrast, saturate, color balance, etc.

Clear skies!

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