How To Take A Dark Frame - General Help and Assistance on using CHDK stable releases - CHDK Forum
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How To Take A Dark Frame

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Offline eheil

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How To Take A Dark Frame
« on: 13 / May / 2008, 17:47:40 »
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Is there any trick to taking a dark frame, beyond "do it in a dark room/with a piece of cardboard over the lens"?

Some button or setting or switch or whatever that tells the computer to take a picture and not open up the lens?

I don't have a lens cap to leave on...

Just curious if I was missing some special trick/option!

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Offline intrnst

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Re: How To Take A Dark Frame
« Reply #1 on: 14 / May / 2008, 03:01:52 »
Welcome to the line.  ;)

Darkframe noise reduction
long exposure- noise reduction = amp glow
"Hot" pixels - awful pictire...

In one of the Barney's deleted messages he commented about this constant absence.

Good luck.

__
Edit: And, at the exact time I was complaining about this...
Developer-friendly / experimental branch (dataghost)
Definitively you're a lucky guy!  :o
« Last Edit: 14 / May / 2008, 05:12:12 by intrnst »
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-- funny english, be aware -- CHDK for Dummies - The Very First Steps
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Offline eheil

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Re: How To Take A Dark Frame
« Reply #2 on: 14 / May / 2008, 09:15:59 »
Wow!  I don't think I'll dare touch that till it's had a chance to make its way into a less scary build, but it's awesome to know it's in the works. :)
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Offline veti

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Re: How To Take A Dark Frame
« Reply #3 on: 05 / July / 2008, 22:01:42 »
maybe time to resurect this ... any progress on one of the CDHK holy grails ... an automatic (script) generated dark frame ?

I want to take X (for astro) night shots at 10 - 30sec exposure plus 1 dark frame at the end to get rid of the hot pixels and the purple monster that lives in the top left corner.

at the moment I take X pics at Y exposure for stacking ... so then must physically be there to manually take the dark frame (by covering the lens) at X-1 (the last shot) to get a decent representative dark frame.

now if I am taking X=25 shots at Y=30 secs exposure (about the limit to aviod star trails) ... that means I have to be at the camera *exactly* (X*Y)-1 (in the example case 12)  minutes later to manually take that dark frame , otherwise the whole previous sequence is useless because the CCD has cooled off , etc. and that makes the generated darkframe useless.

At the moment I have to take X raw frames without NR , then one more at the end with NR , sum the X frames , subtract the X+1 (with NR) frame to create a "dark frame" ... apply that  dark frame to the other X frames to get rid of the noise  ...

and now I read that it seems the camera generates "dark frame" reduction shots by applying the dark frame to the raw *before* the raw is saved  , which makes all my raw generated dark frames useless !

So is there a way yet to simply just close the shutter and take a totally dark shot (of the CCD) to  use as the dark frame ?

or to summarise ... is there a way yet to get a real "dark frame" automtically in a script ?
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Offline fudgey

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Re: How To Take A Dark Frame
« Reply #4 on: 06 / July / 2008, 04:24:45 »
In short: Currently there is no way, but in future there very likely will since the way to do it has already been discovered. If you're up to it, feel free to continue that work.
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Offline cyril42e

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Re: How To Take A Dark Frame
« Reply #5 on: 06 / July / 2008, 12:12:40 »
I've ported this DataGhost's feature to sd1000 without any problem. I asked here: Developer-friendly / experimental branch (dataghost) if it was that simple and there wasn't a problem I could have missed, but got no answer...

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