Beginner's guide to stacking planetary images with AutoStakkert!2

[JamesF]

Last week someone asked about a guide to stacking planetary images using AutoStakkert!2 (hereinafter known as AS!2) and I said I'd write something up. A few days later than I imagined, I've got around to it. This isn't meant to be an exhaustive explanation of how to go about stacking planetary images. It's more of a place to start from. I've ignored many of the options that you can get by without at first and glossed over a few things that you can pick up once you get into the swing of processing.

The sample I'm using is one of my own, taken using a 127 Mak on an EQ3-2 with the dual-motor add-on. I used a 2x barlow with my ASI120MC camera to capture about 3000 frames over five minutes which is well within the limits imposed by Saturn's rotation. As long as you have an AVI file saved using a sensible (ie. non-lossy) codec however, you should be fine and the processing will be pretty much the same. It is possible to use sequences of single images, too. I've just never tried that for planetary imaging.

The first thing I do is preprocess the AVI using PIPP. This isn't strictly necessary, but because the tracking on my mount isn't that great I can't capture data from just a small area of the camera sensor and there's usually a fair bit of empty space around the image. PIPP allows me to crop this off and recentres the image to make the stacking faster and easier. I just load the AVI and check the "Planetary" option to set appropriate defaults:

Then I set the output frame size. As you can see above I had a 640x480 frame in the AVI. In the Processing Options tab I set the output size to be 250x250:

Unless you know why you want to change them, I'd leave all the other options along for now. Hit "Test Options" to get a window to show what the output should look like:

There's clearly going to be enough room around the image, so I'm happy with that. If you've chosen too small a size you can go back and change it. This also gives an idea of the quality of my input data. Once everything looks right, go to the "Do Processing" tab and click "Start Processing". This may take a while...

Once that's done you're finished with PIPP. It saves its output in a new folder beneath the one you loaded the AVI from. The location is given in the output in the window on the right.

Now start AS!2.

Click "1) Open" and open the AVI file written by PIPP. It will display the first frame in a new window:

Click "2) Analyze" and AS!2 will scan the images to decide how good they are, producing a graph in the first window:

The grey lines are the quality of each frame in order. The green one is the quality level with the frames re-ordered by quality. At this point you can decide how many frames to stack in the "Stack Options" box at the top right. With this sort of graph I'd probably leave it somewhere near 50%. If you have lots of poor frames or lots of very good frames you might adjust that to try to use as many good frames as possible whilst avoiding the bad ones. Leave the other options for the time being.

Now go back to the other window with the capture frame displayed. You need to set the number and size of the boxes used for stacking. There's a lot said about box sizes and placement, but to get started and for an image of this sort of size I'd choose a box size of 25 and let it place the boxes automatically by clicking "Place APs in Grid". It may be possible to do a better job than this, but you can always come back for a reprocess on those rare cloudy nights.

Then go back to the first window and click "3) Stack". AS!2 will spend a while processing and eventually tell you it has done 100%:

In the folder where PIPP placed the AVI file there should now be a new TIFF file with a name starting "AS...". That's your stacked image, and you're done with AS!2.

The final stage I do with Registax v6. I click "select" and load the TIFF file. You'll see Registax drops you straight into the wavelets section

The first thing I do is sort the wavelets out. This is a reasonable image for me, so I got really quite aggressive with the wavelets:

If you look at the image now you'll see that there's a slight red/yellow tinge to the front of the rings, and they're slightly blue at the back. It's hard to see, but it is there. Many planetary images will be like this if they've been captured in colour. In fact it's quite rare in my experience for it not to be present. It's due to the atmosphere diffracting the different colours of light by different amounts, shifting blue and red away from each other. Fortunately Registax has a tool to help with this. Click on "RGB Align" in the Functions section. A dialogue box will appear with a green box over the image. Stretch the green box until it surrounds the image with some to spare and then hit the "Estimate" button.

Registax may not get this perfectly right and it may be necessary to tweak the colour shifts manually. See what you think when it's done. You'll also find that some of the sharpness may have disappeared from your image. Don't worry about that for the moment.

Registax has lots of other things you might play with in the Functions section, but for this image I'm mostly happy as it is. It may be worth looking at the Histogram graph and stretching the histogram if the dynamic range of the image is fairly compressed. Hit "Do All" which should apply all the transforms to your image and return the sharpness from the wavelets and then save the finished image:

If you have GIMP, Photoshop or some other image manipulation package you can now do your final tweaks before posting it

James

[stargazerslivingroom]

Fantastic post, James.

This is so useful...Many thanks.

Steve

[knobby]

Nice post, cheers James

[mikehab]

Excellent post James - very useful. The effect of Wavelets in Registax never ceases to amaze me - going from a fuzzy image to an image with clearly defined detail - yet that's the bit of the process that seems to be (in my limited experience) rather "random" and very much a "trial and error" process. If only they could introduce a "Magic Wavelets" button that automatically adjusts and magically fixes the wavelets to produce the final crisp image ;-)

Thanks,

Mike

[Astrosurf]

Greart post James. I'll print it off and have a go!

Alexxx

[redneon]

Nice! Does AS!2 do a much better job at stacking than Registax?

[JamesF]

Nice! Does AS!2 do a much better job at stacking than Registax?

Oh dear. Look at all those worms all over the floor. You are going to put them back in the can, aren't you?

In my opinion... AS!2 produces stacking results at least as good as Registax v6 for planetary imaging and is more tolerant of variable quality data. Both produce better results than Registax v5, but only when v6 works. AS!2 therefore seems like the best choice all round.

Also in my opinion, this is not the case for full disc lunar and solar images when I favour dropping any poor quality data and stacking using Registax v6.

Other people absolutely will give you other opinions

James

[JamesF]

(Oh, and in case you missed it and are interested, I did a separate write-up of how I go about full-disc lunar imaging with a DSLR. I think Roger (Bizibilder) has cornered the market for full-disc Solar and I don't think I could better his posting for that.)

James

[redneon]

Cool. I'm planning to do Saturn shot with my SPC880 over the weekend so I'll give AS!2 a shot and see how I get on.

[yelsac]

Wooow that was quite a walk through, really interesting to see how the experts do it, lots of things to try there.

James I see from other posts you've moved over to firecapture, in your opinion is it better than sharpcap? mind you I'm only using the basic webcam (spc900)

would really like to get Saturn high up in the sky but alas we'll have to wait until 2032 or something!!!!!!

[JamesF]

I'm far from being an expert I think

I moved to FireCapture principally because I moved to the ASI120MC camera and the support was better. I'd say FireCapture has more features than SharpCap, but it's more demanding to learn (though it does have an online reference manual).

I've just upgraded to v2.2 of FireCapture from the beta with support for the ASI cameras and I have to say that I'm finding it a little ropey. I've had a number of lockups that require it being killed from the task manager this week. I think if I were still using my SPC900 for most of my planetary imaging I'd probably stick with SharpCap.

James

[redneon]

I went out last night and captured a few videos of Saturn. I've picked the best one and stacked it with both AS2 and Registax 6 and I think you're right, AS2 just has the edge. See what you think:

AS2:

Registax 6:

I'm a little disappointed with the images, to be honest. I think I had the wrong settings in SharpCap as the sky is really bright. I'm hoping to get out again tonight to try for a better capture. I did 3 minute videos at 15fps with the exposure as high as possible (-4) and managed the visibility of Saturn with the gain. I think where I went wrong, however, was to have the brightness setting too high. It's difficult to see on a laptop screen at 1am, though

[JamesF]

I would not go above 10fps with the SPC900 and keep the exposure set to maximum. Then adjust the gain to give a histogram about 60% to 70% across. I also set the gamma to minimum. I don't touch anything else initially.

James

[leelee970]

James, that was excellent. well done.

Just one question, I adjust the RGB align (and RGB balance) before adjusting wavelettes - do you think that I should do this afterwards?

Lee

[JamesF]

I don't think it will make any difference. I do it afterwards because it's easier to see if the estimated result is optimal after sharpening has taken place. Granted Registax often gets it right most of the time, but on occasion I've had to tweak the offsets to get it how I wanted.

James

[Helite]

I have used this guide half a dozen times now as a reference, thank you for the effort put into writing it James. Sure would make life easier to find if it was pinned too!

[pixelsaurus]

Great stuff James.

[Pete Presland]

nice tutorial! i must give as2 a go

[Steve Ward]

Hi James ,

Great tute  ... Very clear and concise ... 

I notice that you've used the "Wavelets" in Gaussian mode , might be worth highlighting this as Reg generally shows "Linear" mode as a default and there's a world of difference in effect between them , people may get a bit of a surprise if they ramp the first three layers up to 100% in Linear ... 

[JamesF]

Hi James ,

Great tute  ... Very clear and concise ... 

I notice that you've used the "Wavelets" in Gaussian mode , might be worth highlighting this as Reg generally shows "Linear" mode as a default and there's a world of difference in effect between them , people may get a bit of a surprise if they ramp the first three layers up to 100% in Linear ... 

Thanks for pointing that out, Steve.  I must have changed that so long ago that I'd completely forgotten about it.  I dread to think what the output looks like if you push those sliders up to 100 in linear mode.

James

[tich]

I've only just come across this tutorial after I was having some stacking issues with Registax so a great tutorial James, I've been doing a few full moon images using the 80ED & 1000D recently & after converting them with PIPP Registax was having none of it. I tries Autostakkert & it worked straight away. Does anyone know what the drizzle function does? I only ask as I tried it a couple of times but it said that I ran out of memory, most likely due to my ancient laptop that I'm using.

Anyway I was quite pleased with the results I got so hopefully I'll be doing some more full disc lunar images processing them was a bit hit & miss in Photoshop as every one looked different as regards colours.







 

[JamesF]

I've only just come across this tutorial after I was having some stacking issues with Registax so a great tutorial James, I've been doing a few full moon images using the 80ED & 1000D recently & after converting them with PIPP Registax was having none of it. I tries Autostakkert & it worked straight away. Does anyone know what the drizzle function does? I only ask as I tried it a couple of times but it said that I ran out of memory, most likely due to my ancient laptop that I'm using.

Oddly enough, I actually use Registax all the way for my full disc lunar images

Drizzle is a method of increasing the effective resolution of an undersampled image by taking advantage of the fact that it can shift by fractions of a pixel each frame.  That's quite useful for DSO imaging where the image tends to be undersampled, but in my experience planetary and lunar imaging tends to be oversampled.  At that point I think drizzle becomes mostly a glorified resize.

There's an excellent explanation of drizzle here: http://www.stark-labs.com/craig/resources/Articles-&-Reviews/Drizzle_API.pdf

James

[LeeWilky]

mate this is so helpfull thankyou for taking the time to do this!

[JamesF]

mate this is so helpfull thankyou for taking the time to do this!

You're very welcome

James

[LeeWilky]

I seem to be having a problem with the final part of this in Registax whereas my final image is pixelated but in the zoom view very smooth.  Any ideas whats going wrong?

When i save the image i get the pixelated version not the one in the zoom view.