Greetings, all!

I've been a lurker around here for a long time, but haven't started posting until now. As winter approaches and college breaks become available, I plan to start shooting more, but I have a question about image stacking.

I've seen some wonderful compiled images on this forum, and I was wondering how to achieve that same result. What is the best way to align the images to stack them? I've tried before, and the image attached is the result, though it is only two images put together. Any advice on the subject would be very helpful!

- Josh

Attached Images

bestorion.jpg (14.2 KB, 25 views)

Great picture of Orion. A picture of a bright object like the Orion nebula is not likely to improve from stacking.

I use IRIS 5.1 (free ware). Excellent, but the learning curve is steep. It registers N pictures and then adds them together, but I have never tried more than 15. My standard exposure time is 60 seconds. This way the loss is not too bad if a picture has to be eliminated because an airplane goes through. The result is saved as high quality jpeg and final image processing in Photoshop.

hha

If you're willing to spend money, MLUnsold's ImagePlus works well for stacking.

Todd

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

Hello and welcome to the forum. As a relative beginner myself, there are others who will be able to provide a wealth of advice but I will will give you a few ideas to start with.

First, a couple of questions. What camera are you using and what are its capabilities?

For deep space photography, (galaxies, nebulae...), you are gathering light so, in general, the longer the exposure, the greater the depth and colour. So you are stacking fewer long exposures.

For lunar or planetary you are taking lots, ie. hundreds of shots, choosing the best and stacking these to overcome atmospheric interference and enhance features.

For stacking I use registax which is a free download. It handles avi files best so if you are already using a ccd camera it will work well. If you a using a digital camera, the jpeg files need to be stacked manually, ( there is a tick box for this ). To select the shots you want to stack, create a separate file containing only the shots you have chosen to stack.

Open registax and then use the select option to select the files. You will then need to align the shots by selecting one or more alignment points, (prominent features in the frame with reasonable contrast). Once chosen, assuming the alignment features are in a similar position on each frame, registax will proceed on its own. Registax may ask you to select the feature manually on each frame. I have found the selection of alignment points to be more art than science but others may be able to offer some tips here. When finished, select 'Limit', (which controls the quality of the stacked image by limiting pixel differences), and then 'Optimise and Stack'.

Registax will stack automatically. You will then be presented with a battery of powerful image processing tools for limiting noise, enhancing selected wavelengths... At this stage I save the stacked image as a bitmap and then reopen it in photoshop cs2 for processing as I find the tools in photoshop simpler to use. I will eventually bite the bullet and learn how to use some of the histogram and wavelet filtering devices.

Thats enough to start with so good luck and enjoy. I hope others wiil chime in with other ideas for you.

Kind regards
Matt

Useful replies so far, thanks.

winensky: I'm using a Canon dSLR through my telescope (Celestron NexStar 8" GPS) for the deep sky objects, mainly. The camera is capable of up to 30 seconds exposures, but, unfortunately, lacks a setting allowing me to keep the shutter open for an extended period of time without a remote.

As far as other (moon, planet) shots go, I've been using a CCD imager with registax, though I did not know that I could stack JPEG images in there as well, I suspect that I've been blind.

That's just the sort of information I needed, though, and I'll be sure to try using registax next chance I get for stacking regular images.

Thanks!

I suggest getting a remote--the cheapest is basically a hand-held button with a wire to the camera, and if the camera has a "bulb" mode, you can either hold the button in, or with most remotes, it has a lock to lock the button in, and you release when time's up.

Even if you don't want to use the bulb mode, pressing the camera's own button directly starts it shaking, and that really screws up images!

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

Does your camera support RAW files? If so, those are usually 12 bit images while JPG is only 8. You throw away most of your data using jpg! JPG supports 256 intensity levels while 12 bit RAW supports 4096, 16 times more! JPG leaves you little room to process the image. Avoid JPG if at all possible until saving a COPY of the image for the net. The image you archive should remain at the full bit depth your camera takes. Also save the original stacked images as you may wish to try again using a different stacking routine. There are three basic ways of combining images for deep sky work (not planetary), Averaging, Adding and some sort of noise rejection routine. If the image contains a lot of information that is already near maximum brightness avoid adding the data unless your addition routine supports more bits than the camera took. If it saves in 16 bit mode and you took the images at 12 then adding is fine. But otherwise use averaging. Both reduce noise equally.

There are several ways of combining that further reduce or eliminate satellites, cosmic ray hits etc. if you take more than about 6 frames. The simplest is median combine. It finds the median value of all images for that pixel in the stack. Thus if a satellite comes through it's track is ignored. The problem is it doesn't reduce random noise as well as the other two so you need more frames. Better is a form of Sigma Reject. There are several freeware programs that handle this though most only support FITS file format that astro CCD cameras use. These programs use a more complicated routine that often reduces noise more than adding and averaging. It's the only way I go any more when I have 6 or more frames to stack.

I've heard Registax supports it, I don't know personally however.

Rick

RickJ: That was excellent information, thanks for taking to time to write that up. Yeah, the camera supports RAW images, though I have not been shooting in that format, sounds like it will make a distinct difference. I suppose that most of the work will be trial and error at first, but that's as good a way to learn as any.

Thanks for the information, though, it provides a good place to start.