Since we’ve been going back and forth to the LRE house and I haven’t had a chance to get things fully set-up in LA for CCD imaging, my main target has been the Moon. As in the previous post, I have tried additional mosaics. I have also kept experimenting with processing Lunar images.
My basic process in PixInsight is:
- Convert the image to 32 bit
- Upsample by 200%. Deconvolution simply won’t work on the original pixel depth.
- Use regularized Van Cittert algorithm deconvolution to sharpen the image
- Flatten the image with HDR Wavelet transform at the default settings
- Adjust the contrast of the image with curves
- In some cases, do some minor noise reduction with GreyCStoration.
Most of my time is taken tweaking the deconvolution parameters. (If you are starting on this, the PixInsight team has a great processing example on their site.) This time, I learned that other parameters matter too.
In iterating on the deconvolution, I noticed that this image had more noise that other recent ones. The deconvolution was bringing it out clearly. After several hours, I figured out what I had done differently. On my prior Lunar images, I had selected bicubic b-spline interpolation rather than default when I upsampled the image. No particular reason, but I picked that instead of the default. This time, I had used the default (“automatic”) which I believe chose bilinear interpolation.
No, I don’t understand the difference in the algorithms, but I know they are different. Time do do some reading on the subject.
So I experimented and learned that for my Lunar images, bicubic b-spline is sharp, cubic b-spline produces less noise, and the other offered choices aren’t worth using. And I learned that you can go past critical details in processing your image without even knowing it. Layers. (Onion layers, not parfait layers, if you follow the reference.)