Posted 20 February 2013 - 09:57 AM
The breakthrough was to resize the drizzled stack BEFORE applying wavelets. I made this intellectual leap while reading another thread. It occurs to me that resizing before wavelets makes all kinds of sense, given what wavelets do.
So, is this common knowledge and I've simply been doing a silly thing? (I also post in case anyone else is missing this step).
For what it's worth, I got very nice 1.5x and 3x drizzle stacks from one of my nicer Jupiters. I can't say it's obviously better than without the drizzle, but at least it's not a fuzzy mess.
Posted 20 February 2013 - 10:27 AM
Posted 20 February 2013 - 10:54 AM
Posted 20 February 2013 - 12:19 PM
Then you are basically not using drizzling for what the technique actually does: increasing resolution for undersampled images.
If resized to the original size there is no real image improvement, except for perhaps an unmeasurably small improvement of alignment accuracy. You might as well just go for the 9x faster normal processing.
Furthermore, the effects of the image resizing algorithm you used (yes, resizing messes with data!) is probably much bigger than what drizzling did to the image. Resizing usually either blurs or sharpens the image a bit, so there is no way to directly compare an original stack and a 'resized back to original size' drizzled stack, making it pretty much impossible to make any valid claims regarding 'drizzling'.
Posted 20 February 2013 - 12:30 PM
In that case, drizzling has never yielded a usable image of any sort - it is fuzzy to the point of almost no detail and when any of the various sharpening techniques are applied, the image only gets worse (this includes wavelets in R6 and LR deconvolution in AstraImage).
In that case, can you think of what I'm doing "wrong"? Is it simply a case of the data isn't undersampled, so there should be no improvement with drizzling?
Posted 20 February 2013 - 01:10 PM
Likely, but that doesn't mean the image should look bad.
You MUST however adapt your further processing to the drizzling output (e.g. use coarser sharpening, deal with potential artifacts, etc etc..)
Perhaps it is a good idea to just show your images, otherwise it will be difficult to give pointers.
Either way, drizzling IS NOT just a magic make-my-image-look-better option. With careful processing it CAN make your image look better under certain conditions. With careful processing there is no reason it should make your images look worse.
Posted 20 February 2013 - 07:10 PM
My "conversion" came by way of the ASI120MM where although I haven't done the maths I am almost sure I am under-sampling with all the images I have captured to date.....sure I am waiting for the opportunity to use a greater image scale but imo seeing has to co-operate as well for optimal outcomes regardless of the maths, and I just haven't experienced what I'd term "very good' seeing so far.....
So, if my assumption about under-sampling is correct then my findings would be a neat demonstration of what Emil stated above - that is, I find my ASI120MM images respond extremely well to 3X drizzling in AS!2.....with the (also) stated harder/coarser wavelets applications part of the pre-requisites!
...just my 2 cents worth!
Posted 20 February 2013 - 08:36 PM
And, Emil, I apologize if it came off like I expected a magic bullet. I don't. Although, I must say, I find AS!2, in general, to be a magic bullet, so I can't really ask for two bullets!
My only concern is I hear tell of drizzling being a useful tool from some folks whereas it does either nothing or worse than nothing to my images. In such situations, I usually assume I am the problem. I'll dig up some attempts tomorrow and post.
Posted 21 February 2013 - 12:40 AM
Posted 21 February 2013 - 06:12 AM
So, at this point, I'm willing to conclude that my problem in other images is that they're oversampled to begin with.
Posted 21 February 2013 - 07:17 AM
Drizzling was designed for undersampled images and doesn't really work if they are over sampled (as stated above). Have you tried doing LR decon on your Nyquist/oversampled images and then reducing to native capture size? I've found that can work. Naturally, all of this is seeing dependent.
Posted 21 February 2013 - 08:57 AM
So, Paul's point is, drizzle before wavelet sharpening. Emil's point is, don't take image back down to native resolution because there is little benefit from drizzle used in this manner. About right?
Posted 21 February 2013 - 05:40 PM
I put this up in the solar forum but I'll link it here, too. This is a mosaic of 9 panels shot undersampled through a PST. The images were stacked in AS!2 with 1.5x drizzle and the resulting images sharpened and behaved like an image should. So, I think I'm now down with drizzling.
Posted 21 February 2013 - 10:33 PM
Posted 22 February 2013 - 11:48 AM
In terms of processing I've always done a 1.5x upscale or even 3x for Mars either using ninox or AS2. I never really thought much of drizzle/resize and it's relation to image scale / focal-ratio.
For certain in poor seeing the same optical train and processing gives me all sorts of fits for artifacts etc, especially on Saturn at full gain!
I'm favorit'ing this thread to come back to later for sure, nice job Paul's, Emil, Tim and Darryl!