Okay everybody, I've got a bit of a `thinker' for you. I suppose this is mostly directed at the PI authors and gurus, like Juan, Vicent, etc..., but I'd be curious to hear anyone's opinion.
Many of us have commented on the difficulty we commonly have when choosing parameters for PI's processes, such as Deconvolution, MMT denoising, StarMasking, etc... We are often somewhat overwhelmed by the number of things to adjust. I'm always very grateful to read, say, one of Juan's tutorials on noise reduction or deconvolution, in part because he gives us useful settings to try as a starting point.
It's finally starting to dawn on me that the VaryParams script could be pretty useful here. I've known about it, and I've had it saved on my computer for a while, but I've finally started trying to use it to help me figure out some Deconvolution settings for an image. Here's what hit me the other day: It's like starting an imaging run! Setting VaryParams to explore a parameter is kind of like setting my telescope/mount/camera on a run of light frames. I go off and do other things, such as observing with binoculars (in the case of an imaging run) or doing something else on the computer (in the case of VaryParams). Okay, so far so good.
Here's what I'm wondering... for a given process, such as Deconvolution, how much does the ORDER of our explorations matter? For example, in Deconv, the `Global Dark' setting matters a lot. It wasn't until I read Juan's tutorial on Deconvolution (
http://pixinsight.com/forum/index.php?topic=2727.msg18512#msg18512) that I found out it should be set to a very low value, such as 0.005. If I'm trying to use VaryParams to explore the parameter space within Deconvolution, I might start my exploration by doing several Deconv runs with different values of Global Dark. Once I find the best value, I might go on to some other parameter.
But here's what nags at me: What if the parameters affect each other so much that we can't take this `sequential exploration' approach? What if, having found a Parameter X that looks best, the optimal Parameter Y (or whatever) would actually necessitate going back to Parameter X and re-tweaking it? In such a case, it seems to me that our exploration of `Pixinsight parameter space' is fairly close to hopeless, without some massively automated AI system doing it for us.
So, my question boils down to this: In most of PIs major modules (Deconv, MMT denoising, etc...), will we get good results if we iterate parameter-by-parameter, sequentially? And more to the point, *what order of parameters should we use*?
I think that if the PI Team could give us a simple list of the `parameter order' for each processing module, these lists would be some very powerful information for PI users. We'd know what order to use VaryParams, and then processing in PI becomes like shooting a celestial object with a CCD camera and autoguider... just set it up and let it go. Forget that manual guiding with the illuminated cross-hairs, go take a nap or look through a visual scope or do something that you actually enjoy. In the case of PI, forget staring at PI all day, just check on it from time to time to see if you need to set VaryParams on some new task, and go live your life. True, processing wouldn't *really* become a brainless, automated task. A reasonably deep understanding of the methodology of imaging and the workings of PI will still be necessary, as well as an aesthetic sense. But this just seems to be a way to harness the power of a computer to do our iteration for us, instead of staring dumbly at the PI screen, as I do.
So, to make this work... what is the preferred order of `parameter exploration' for each of PIs modules? Hmm? If we have this, we can (sort of) all become PI wizards like the gurus we admire so much! (There's some tongue-in-cheek exaggeration there, of course.)
Wait a second! Now I know what image processing (particularly with PI) is like! This is a problem in cryptanalysis! I can finally put my finger on what processing feels like. The correct set of parameters to apply in PI, which would yield the best possible image (according to my aesthetic sense), is the plaintext. The image data are the ciphertext. PI is the Engima Machine. It has `rotors', `reflectors', plugboard settings, a day key, and the like. VaryParams is like one of Turing's `bombes', or his Colossus. It has the power to help me explore parameter space and make progress on the decryption, but it isn't strong enough to do the whole process by brute force. Ideally, different parts of the decryption process could be isolated from each other, so it could be done in a piecewise way. To the extent that the different parts of the decryption *can't* be isolated from each other, the task becomes more hopeless.
My dream of the `parameter exploration order lists' would be like telling Marian Rejewski or Alan Turing what parts of the decryption process could be isolated from which other parts, thus allowing their machines to do as much of the work as possible.
- Marek
- Marek Cichanski
