Defective pixel removal

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roelb
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Joined: Wed Mar 08, 2017 11:36 pm

Defective pixel removal

Post by roelb » Sat Aug 04, 2018 1:16 am

Would it be possible to accomplish a automatic hot pixel removal during stacking?
"Starlight Live" software from Paul Shears has a "defective pixel removal" incorporated.

Thanks in advance considering this request.
Regards,
Roel
Roel
Celestron Nexstar Evolution 8 - Celestron Nexstar 6 SE - OTA 5 SE - StarSense
Starlight Xpress Lodestar X2 Mono -- ATIK Infinity Colour -- ZWO ASI290MM -- ZWO ASI224MC

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admin
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Re: Defective pixel removal

Post by admin » Sat Aug 04, 2018 1:09 pm

Hi,

this is built into the dark frame subtraction feature (so you have to use a dark frame...) Any pixel in the dark frame that is more than six (I think six, maybe seven) standard deviations above the mean is treated as 'hot', meaning that a neighbouring pixel value is used in the final dark subtracted image.

I guess you are asking for this to be available without a proper dark frame, just a hot pixel map of some sort?

cheers,

Robin

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turfpit
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Re: Defective pixel removal

Post by turfpit » Sat Aug 04, 2018 6:10 pm

Roel

Doesn't the Pre Processing option https://docs.sharpcap.co.uk/2.9/#Other%20Controls already do what you require?

Dave

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Hibou
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Re: Defective pixel removal

Post by Hibou » Sat Aug 04, 2018 7:10 pm

I think Roel (and I) would like to see "real time" hot pixel removal, without the need for dark frame or hot pixel maps. This might be done by using the code you already have for hot pixel filtering in dark frames and having it as an option to apply to each image frame in real time. I guess even stars are not usually resolved to a single pixel; in any case, it could be turned off if it eliminated too many stars :-)
Cheers, Alan.

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admin
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Re: Defective pixel removal

Post by admin » Sat Aug 04, 2018 9:29 pm

That's an easy thing to get badly wrong - search for 'Nikon star eater' and you will discover that a hot pixel removal algorithm in early Nikon DSLR cameras had very undesirable side effects for astrophotography!

cheers,

Robin

roelb
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Re: Defective pixel removal

Post by roelb » Sat Aug 04, 2018 11:14 pm

Indeed I would like to see "real time" hot pixel removal, without the need for dark frame or hot pixel maps.
This is done successfully in StarlightLive.
Roel
Celestron Nexstar Evolution 8 - Celestron Nexstar 6 SE - OTA 5 SE - StarSense
Starlight Xpress Lodestar X2 Mono -- ATIK Infinity Colour -- ZWO ASI290MM -- ZWO ASI224MC

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Hibou
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Re: Defective pixel removal

Post by Hibou » Sun Aug 05, 2018 5:19 am

Yes, people who want to see faint, single pixel stars have to be very careful to distinguish them from hot pixels, so will use pixel maps, dark frames etc with post-processing. But sometimes we just want to see things in real time. The increasing popularity of live stacking software like Atik Infinity and Starlight Live demonstrates that.

Yes, Nikon should have had an off-switch for image filtering, to output true RAW images, but even Nikon can't foresee all the possible applications of their hardware... or software.

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