Why we derotate images & videos when doing planetary image processing (Niall MacNeill)

Why we derotate images & videos when doing planetary image processing

Acquisition type: Lucky imaging

This is a blink animation I made to show why we use software to derotate planetary images before integration.

I captured Jupiter with the IR 850nm BP filter. This filter is further into the infrared and the light getting to the sensor is less due to the fact Jupiter produced less light at this wavelength but more particularly the sensitivity of the sensor drops off at longer wavelengths. Therefore to get enough data it is convenient to video the planet for say 10 minutes at relatively low frame rates. You may recall that for visible light I normally limit the video duration to 1 minute to ensure no loss of detail due to the planet’s rotation, which causes details to be smeared. This is because the longer the video the greater the difference between the first and last frames which are being stacked together.

When I process the 10 minute video, I use WinJUPOS to derotate it first. As I understand it the software goes to each frame of the video and converts the spherical projection of the planet to a cylindrical projection and rotates that frame to the midpoint Universal time stamp, since it knows the UT timestamp for that frame. It then converts the derotated image back to a spherical projection. It does this to each frame to create a derotated video, which I then process in the normal way….using Autostakkert to quality check and then based on my input, reject the unwanted frames before stacking the remainder. The image is then wavelet sharpened in RegiStax.

Image B is the final result, north up versus the video which was south up.

Final
Original
B

B

Description: Final processed image, north up

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