Saturday, October 29, 2022

Putting It to the Test

One of the many sections of ALPO[1] is the Online section, of which I’m an assistant coordinator. While currently this means I’m focused on helping to maintain the organization’s website and post observations to the galleries, I think there can be more to the section.

Born as the “computer” section in response to the PC revolution and its impact on our hobby, the original aim was more towards what sort of software was available to assist the amateur planetary observer. To me, this has more relevance than ever given how integral software has become in processing most observations today.


There are many competing products out there that one can choose to align, stack, sharpen, and tweak their video capture into a valuable image that documents the state of an astronomical body for a given point in time. Less available to the amateur observer is a sense of how the software works or what approach is preferred (or should be avoided). Often the individual approaches it as a bit of a black art, playing with settings in the interface and seeing if the outcome is better or worse. While the learning curve is perhaps not as steep as with something like PixInsight for our deep sky imaging brethren, there are still many nagging questions when doing a planetary imaging workflow – “Am I doing this right?”

This is where I believe that the ALPO Online section has a role to play harking back to our roots as the “technology” arm of the organization by conducting studies to shed light on common questions. As an example, when setting alignment points on an image in preparation for alignment & stacking, what size works best? How important is that? What is the current theory on it, and does that theory hold when tested? Questions such as this are not just academic, their answers can impact the quality of our output.

With all this as background I’m announcing an effort to tackle some of these software setting questions. Lifting a page from the Zooniverse folks, my idea is to generate a set of images where, to the best of my ability, all parameters are the same except for one and then invite the amateur community to score them. With a sufficient number of evaluations, it should be possible to make a statement (and perhaps a recommendation) on the optimal setting to use when processing your video into a final image.


I have defined my first inquiry and worked up a set of images to use in the test. The posit is that when processing a video taken under only fair seeing it is better to use larger alignment points, whereas a capture under very good seeing benefits from smaller sized alignment points. The theory is well explained by Christophe Pellier in Chapter 7 of his excellent book Planetary Astronomy:

“An AP is defined by small boxes and the alignment will be done based on the details that are present inside of it. If the image is noisy and with low contrast, a size that is too small will prevent the software from performing a comparison because of a lack of detail found in some of these boxes. On the other hand, if there is considerable detail present a smaller size AP will increase the accuracy of the alignment.”

Perhaps I am tilting at windmills here in thinking that I’ll get enough participation, who knows? I’m hoping to be able to not just confirm the theory but to also offer some qualitative assessment of its impact on one’s resulting image. If you would like to participate in reviewing the six sets of images, please visit my new ALPO Research & Investigation web page that I am hosting on my personal website until such time that it proves viable and suitable for deployment on the official ALPO website. And thank you in advance for your time if you do decide to participate!


[1] Association of Lunar and Planetary Observers