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JamesF

Registax v6 vs. Autostakkert!2

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I've reprocessed a few of last week's Jupiter images tonight because Space Cowboy enquired as to why I wasn't using AS!2 for stacking and I've been meaning to return to give drizzle another go as well.

So, here are the results for three images taken last week with three different processing treatments. I've processed them entirely within Registax v6, stacked in AS!2 and used wavelets in Registax v6, and stacked with 1.5x drizzle in AS!2, used wavelets in Registax v6 and downscaled to match the size of the originals.

In each of the three sets the last image is the drizzled one and I think it's rubbish compared to the other two. Where the non-drizzled images are concerned, I think it's a very close call. I'd go with the first image by a gnat's whisker in the first two sets after a fairly microscopic examination and I just can't split the last pair. What do you think?

sample-1.png

sample-2.png

sample-3.png

If anyone believes that the drizzled versions could be processed differently to improve the results or would like to see the full size versions, please do say.

James

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They really are super images James. I totally agree the drizzle shots lack the strength of detail and this proves to me that drizzle is less effective with a small scope.

As you say only the last set of images shows a clear advantage to the as!2 version where there is a crack on the reg6 image.

For me the biggest adantage of as!2 is its speed allowing for more experimentation of stack sizes etc and its superior consistancy in all seeing conditions. Another plus is when stacking moons. Unless tracking is spot on Reg 6 fails to produce good moons. I've had them moving all over the show during a 3 min avi and as!2 nails them perfectly.

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I agree, the first two are very similar, and the third is a softer with less contrast. You could argue it's more natural, but only because it de-emphasises the detail.

I've seen several posts where people have been 'converted' to AS!2, but I'm seeing very similar results. Perhaps if you have a really high detail image to start with there is more difference.

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I think on the grounds that I really do struggle to tell the difference between a Registax image without flaws and the same data stacked in AS!2, I might start using AS!2 for preference for planetary processing. This probably means I need to go back to some of my solar and lunar images and try those again. Last time I tested with a solar image Registax clearly did the better job, but it might be interesting to play with drizzle on a solar image to see how it works there.

James

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I use a routine in CS6 for upscaling images. Basically I resize in increments of 1% until I reach the size I want or the image becomes pants. How this compares to drizzling I'm unsure as I don't play with the drizzle functions in Registax or AS!2. I have noticed that depending on the image data that sometimes one programme is better than the other so I do try both programmes to see what they produce

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Just to add another iron to the fire...

I have recently found running the images thru PIPP first, then AS!2 works wonders. With the 18 AVis I took the other night, only 2 or 3 of the Barlowed images needed wavelet tweaking in R6.

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Got to admit that I throw just about everything through PIPP these days :) Short of putting it on a pier there doesn't seem to be any way to completely iron out the "bounciness" of my EQ3-2, so being able to align my solar, lunar and planetary images before letting a stacking program loose on them is really helpful.

James

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Just a quick question: have you change your processing when working with the drizzled image? To me it appears that you simply applied the exact same wavelet scheme with the 1.5x drizzled and normal sized images, which of course is not a good idea. The effect of the size of sharpening filters (wavelet scales, etc) is absolutely huge. That is one of the reasons it is so difficult to compare drizzled versus non-drizzled images.

Drizzling also inherently makes images a bit cripsier (noisier perhaps even). You have to take this into account when processing the stack.

You could downsize the drizzled image before wavelets ( 66.67% should do the trick in this case), but then you also have to think about which kind of resizing method you will use. All of them have different properties, and many of them make the image a bit smoother (bicubic) than it really is, or sharper (lanczos, etc).

By the way, the 1.5x drizzling in AS!2 is actually just 3x drizzling downsized to 50% using a bicubic resize filter.

Having said all that, I find that for normally sampled images there is no need to use drizzling, unless you just want a bigger image, than it is fine to use it (but be ware of potential drizzling artifacts, so you HAVE to adapt your processing for optimal results). Only if you really under-sample the images you might see a small improvement in resolution. I have seen this especially in deepsky images of globular clusters, where the stars in the drizzled image were slightly smaller, and stars touching in a normal stack were actually separated from each other in the drizzled image. Drizzlig also relies on VERY accurate sub-pixel alignment, this can also be the limiting factor. If the uncertainty in alignment is larger than sub-pixel level, there is no advantage to drizzling.

Now back to the original comparison images. What settings did you use for Registax or AutoStakkert!2? The size and location of the APs are essential, as are the quality estimator settings, and the amount of frames you chose to stack. I just want to point out that testing is actually rather difficult. Of course you can say this is a test that shows what YOU can do with both Registax 6 and AS!2, and those tests are indeed very helpful (!), but it does not have to reflect of what is possible in each of the programs. I'm not an expert on Registax 6, so I can't help you there, but I do know a bit about AS!2 and I'm always willing to give some pointers. I also just started a yahoo group on AS!2, for those interested: http://tech.groups.yahoo.com/group/autostakkert

About pre-aligning images: this shouldn't be necessary in AS!2. If you find AS!2 has trouble with stabilizing specific recordings, I would be more than happy to see what I can do about that.

Cheers,

Emil

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Thanks for your comments, Emil. That gives me plenty to think about.

James

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.. The size and location of the APs are essential, as are the quality estimator settings, ..

I've spent no time at all with these settings? Is there a guide somewhere with further info?

To be honest all I do is click NEXT, NEXT, NEXT and play with the wavelet sliders. I know there's so much more to these programs but I don't know where to start!

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Got to admit that I throw just about everything through PIPP these days...

James

I love using PIPP. It saves time in both Registax and AS!2 to align and process the images and the results come out much better.

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As for the images, I'd say that the first in each is great. The second has almost as much detail but has too deep red bands to look all that natural. The 3rd in each set shouldn'y even be a challenge for anyone. It's off the list already.

Josh

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