The main problem with stars and things you want to photograph is that they're so dim. Very little light reaches the earth from a dim star, so just pointing your camera at the sky and clicking the shutter will only capture a few of the brightest stars. Ideally, you want to leave your shutter open for as long as possible, but there are problems with this.
Firstly, the stars move around the sky, so on any exposure above about 15 seconds the stars will stretch out into curved streaks. This is a cool effect if it's what you're after, but if you want a picture of the sky as it appears to your eyes it's not helpful.
The second problem is that digital cameras pick up stray radio signals, cosmic rays, thermal vibrations and all sorts of other things which aren't starlight.
Thirdly, most cheap digital cameras will only take single exposures for a maximum of 15 or 30 seconds. An SLR with bulb mode will happily leave the shutter open for as long as you want, but this demo that will work with any camera. Fortunately, stacking images can get rid of all of these problems and increase the amount of detail visible in return for a little effort.
How Does It Work?
This step is more about the theory of how stacking works- if you don't care about random distributions and would rather get going, feel free to skip it.
Roll a dice once and you might get any result from 1 to 6. Roll it a thousand times, and you can be pretty sure the results will average out to about 3.5. If the results average to a different value, you can be fairly sure your dice is loaded. There's no way you could know that from a single roll, but by taking the average of lots of rolls you can see the pattern of behaviour. The camera works the same way. If you take a single photo in the dark, it will look speckly. This is because of the random signals, or noise, the sensor picks up. This noise obscures the actual subject of your photo and means you can't tell what is a speckle and what is a dim star.
Taking lots of photos is the equivalent of rolling a dice a lot of times- you are taking a lot of samples of each individual piece of sky and taking the average brightness to eliminate random variations. The average value of a pixel that was pointing at a star will tend to be slightly brighter than a pixel that was pointing at dark sky, but this difference might be smaller than the random variations on any single photo.
In general, the more photos you take, the more uniform the background noise becomes after averaging and the more detail you can pick out. A statistician would say that the averaged photo contains more information than a single exposure- there's more meaningful detail.
Once you've got a composite made of the average of many photos, you can tweak the levels with image editing software so the background is the black you expect from the night sky and the stars stand out.
With ToupView, you do not need to snap the image one by one. You can use the Record function on the control panel to record a video run 1000 or more frames for stacking.
You can download the Video to test the algorithm effectiveness.
ToupView is doing a few tasks that you can do by hand, but it's incredibly tedious. Firstly it reads the 2 video frames and aligns the two frames so that the stars are in the same place, then stacking it. The two stacked frame as a new frame will be took as the first frame and ToupView will read the 3rd frames, then ToupView will continus do the same alignment operation with this two new frames untill the end Video frame.