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    Default Stacking Software



    Following the suggestions at the Forum I have begun to play with imaging software. I think I have my camera dialed in with the exception of a few little tweeks. My question is this: Is there a tutorial that will take me, in simple terms, step by step, through the process of stacking. I have both Registax and DeepSkyStacker. I'm not sure I understand the instructions enough to get the images in the order required or maybe I'm missing tasks. Is there a plain language (layman's terms) playbook that will help?
    Hope this is posted in the correct thread.
    Mitch

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    Default

    Out of the two Deep Sky stacker is the easiest to use

    Probably about six steps in all for stacking and processing before saving the file in DSS and if you print of the manual its fairly easy to follow

    If you have any problem with DSS just ask

    Cheers

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    Default

    Deep Sky Stacker for deep sky stuff and Registax for Moon and Planets. Each is not very good for doing the other.

    Trevorw - Do you do anything markedly different from the default setings for DSS ?
    "Oh no! Not another !@#$% hobby" - The wife.

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    Quote Originally Posted by SteveB View Post
    Deep Sky Stacker for deep sky stuff and Registax for Moon and Planets. Each is not very good for doing the other.

    Trevorw - Do you do anything markedly different from the default setings for DSS ?
    No nothing markedly different on DSO just use Kappa Sigma Stacking instead of Median, and use per channel background calibration, set black point to 0 in preferences and sometimes try different options to see what affect they have.

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    Default

    Thanks Trevor, great information there. I am confused a bit about Stacking software. Does it only reduce noise?

    What about increasing dust / gas clouds, and adding more fainter objects with more photos processed? Sorry for the newb question...
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    Quote Originally Posted by admin View Post
    Thanks Trevor, great information there. I am confused a bit about Stacking software. Does it only reduce noise?

    What about increasing dust / gas clouds, and adding more fainter objects with more photos processed? Sorry for the newb question...
    My understanding is that the idea about stacking software is to layer multiple images so that you increase the signal to noise ratio data thereby giving you something to work with in Photoshop or the like.

    Stacking doesn't reduce noise in the base images, noise is a product of multiple factors, temperature, light pollution, how hot the sensor gets etc. Darks and flats are stacked inclusive of the image frames to reduce the noise level (me thinks noise created in a dark frame is offset agsint the same noise in the image frame thereby cancelling it out) in the final stacked item. Likewise such things as a cooled camera, dark site less LP help reduce noise levels in images.


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    Default

    Trevorw, you have the right idea. The theory behind stacking frames does increase the signal to noise (S/N) ratio. Since most of the noise is actually random, you can increase the S/N by Calculating the average of each pixel.

    For example, say that we have 5 frames that we want to stack. To keep it simple, we are using a gray scale with 0=black and 10=white. For the first pixel we want to average, each frame has a value of 5,7,4,6,1. The average is now 4.6, but is rounded to 5 by the computer. For the second pixel, we have a black background, so the values are 0,1,1,0,2, thus averaging to 0.8, which is rounded to 1 by the computer. If the real data (what we see) is actually 5 and then 1 for the each pixel, then we have successfully approximated the real picture.

    I personally still don't understand how darks and flats are included mathematically, but they help out by removing the static noise that is generated by the CCD chip characteristics and the optics of the telescope, respectively.

    flyingcadet

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    Flyingcadet,

    You're right on the money with your description of how stacking removes the random noise. The important part for stacking to work is that the noise is random while the signal (image) isn't.

    Darks - The CCD is not just sensitive to light. It is sensitive to heat as well. If we take an exposure with no light (dark frame), we won't get a zero value because of the heat. The good thing is that the heat generated image is fairly constant so if, using your example, we always got a count of 2 in every pixel due to heat, we can just do a straight subtraction to remove the offset.

    Flats - The light reaching the sensor isn't always uniform. The most obvious example is vignetting, but there's also crud on the optics, sensor, etc. So if you had something that reduced the number of photons by half, the influence of the noise (which isn't reduced by the optics) is effectively doubled. A flat field (a picture of a uniform surface) gives the software the ability to adjust the image to even it back up. It does that by setting the mid value to 1 and then multiplying your image data by the reciprocal of the flat-field.
    So if you had an area that reduced the light to 80%, then you correct for that by multiplying that area by 1.25 (1/0.8) which will bring it up to be 1 right across the image.

    Steve.
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