Author Topic: optimized image subtraction  (Read 802 times)

Offline frasax

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optimized image subtraction
« on: 2017 May 09 10:41:45 »
Hi,

i´d like to subtract two images but don´t want to simply use pixelmath. Both images should first of all be adjust to get the same stars FWHM, the same Signal Levels and Background Levels. So in the End there should be no Artifacts from not matching stars, or negativ values, because of mismatch of signals.
Does anyone have an idea, how can i reach that goal without just try and error (which works, but i´d like to optimize this)?

CS Frank


Offline Carlos Milovic

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Re: optimized image subtraction
« Reply #1 on: 2017 May 09 11:56:32 »
Linear fit?
Regards,

Carlos Milovic F.
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Offline frasax

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Re: optimized image subtraction
« Reply #2 on: 2017 May 09 12:12:30 »
Hi Carlos,

what could Linear Fit do? Leveling the Background or the Signal? It can´t level out the Starsize i guess.

CS Frank

Offline Carlos Milovic

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Re: optimized image subtraction
« Reply #3 on: 2017 May 10 08:07:25 »
It will multiply the signal and add a pedestal so the RMSE between them is minimum.
If you have different PSFs due to changes in the atmospheric conditions, then there is no way to match them (other than degrading one image).
Also, due to Poisson statistics, I would say that an error map (difference) will still show greater variance inside/around the stars.
Regards,

Carlos Milovic F.
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Offline georg.viehoever

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Re: optimized image subtraction
« Reply #4 on: 2017 May 10 11:30:18 »
Georg (6 inch Newton, unmodified Canon EOS40D+80D, unguided EQ5 mount)