Astrophotos?

Question

the astrophotographers take mutiple images of an object and then stack them to get the image. Why dont the take one image,duplicate it on the computer,say 50 times, and stack those?

Answer 1

Each image contains a little bit of "noise", in the form of random pixels. When you take 50 different images, the noise is in different places each time, but the stuff you want to see is in the same place. When you stack those 50 images, you're adding up 50 star images in one place. But a given pixel is probably affected by noise only once, so there you're adding 49 good pixels and one bad pixel. The result is that the noise is only 1/50th of what it is in a single image. If you stacked 50 copies of the same image, the noise would be in the same place each time and you wouldn't get any improvement over a single image.

Answer 2

I would just like to add something to Injanier's excellent answer.In addition to noise, there is another enemy of the Astrophotographer present in the image, the earth's atmosphere!
It is never perfectly steady and so constantly distorts the image slightly. This is especially bothersome when looking at planets. the effect is somewhat similar as if you were trying to look at the object on the bottom of a swimming pool. the fine details visible on Jupiter for example are constantly being blurred by the atmosphere with short periods of steady conditions in between. By stacking and comparing many images (sometimes hundreds of them) some programs can pick out the sharpest images and increase the sharpness of the overall result greatly.
You would be surprised to see how terrible some of these images look when they first come out of the digital camera. You would be tempted to throw them out.! The results after processing are really astounding.

Adolph

Answer 3

I don't understand.What's your point?