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  1. #1
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    Default Can the same photo be stacked?



    I haven't tried any stacking yet, but i' ve been reading a bit about it and i know you add many pictures of the same object together, but why not just stack the same photo? Surely that would do the same thing and cut the need for alignment. I'm obviously missing something.

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    Quote Originally Posted by lifeofbrian View Post
    I haven't tried any stacking yet, but i' ve been reading a bit about it and i know you add many pictures of the same object together, but why not just stack the same photo? Surely that would do the same thing and cut the need for alignment. I'm obviously missing something.
    Here's what you're missing:

    A photo contains is the sum of an object (say a nebula) and noise. By stacking the same photo over and over, the result becomes exactly the same as the original image (no improvement).

    However, by taking different, consecutive photos of the same object, the noise will differ between each picture. Assuming the noise is random and zero on average, stacking these photos will reduce the noise but enhance the nebula, which does not differ between shots (assuming proper alignment).

    Cheers /Patrik
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  4. #3
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    Default

    Quote Originally Posted by lifeofbrian View Post
    I haven't tried any stacking yet, but i' ve been reading a bit about it and i know you add many pictures of the same object together, but why not just stack the same photo? Surely that would do the same thing and cut the need for alignment. I'm obviously missing something.
    What I think you're missing is:

    1) the point of stacking is to reduce noise but retain the original (non-noise) signal so that whatever signal is there can be stretched in tools like photoshop to recover the (very under-exposed normally) image

    2) one photo only has one "lot of noise" in it, so if you stack it with itself the software can't tell it is noise! Noise is something that is different from one stacked image to the next one. Different photos will have different noisy pixels in different places and the software can subtract them

    So, stacking maxmises the "signal to noise ratio" by eliminating things that change between frames (like noise).

    That's a very simple explanation - does that help?

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  6. #4
    lifeofbrian's Avatar
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    Ah nice one, that explains it all, i knew there had to be a good reason why, thanks.


    Quote Originally Posted by Phil Leigh View Post
    What I think you're missing is:

    1) the point of stacking is to reduce noise but retain the original (non-noise) signal so that whatever signal is there can be stretched in tools like photoshop to recover the (very under-exposed normally) image

    2) one photo only has one "lot of noise" in it, so if you stack it with itself the software can't tell it is noise! Noise is something that is different from one stacked image to the next one. Different photos will have different noisy pixels in different places and the software can subtract them

    So, stacking maxmises the "signal to noise ratio" by eliminating things that change between frames (like noise).

    That's a very simple explanation - does that help?

  7. #5
    lifeofbrian's Avatar
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    Now i get it thanks.

    Quote Originally Posted by patpaa View Post
    Here's what you're missing:

    A photo contains is the sum of an object (say a nebula) and noise. By stacking the same photo over and over, the result becomes exactly the same as the original image (no improvement).

    However, by taking different, consecutive photos of the same object, the noise will differ between each picture. Assuming the noise is random and zero on average, stacking these photos will reduce the noise but enhance the nebula, which does not differ between shots (assuming proper alignment).

    Cheers /Patrik

 

 

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