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Badpixel Mapping for Different Exposures

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Offline NewbieToobie

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Re: Badpixel Mapping for Different Exposures
« Reply #40 on: 22 / July / 2008, 19:51:49 »
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It seems, on my camera, that the same pixels get warmer than others even after being tested days apart. I was using the same files I created 3 days ago at 64 second shutter speed to test the function today. The same extra-warm pixels were in the same locations. Keep in mind that I only filtered out pixels with values higher than 129 as a threshold. The main random, and much darker, noise was left behind. So yes, you can use old files on long exposures. I understand how even stray cosmic rays can temporarily produce a warm or hot spot. There were a few warmer pixels that were in new places but the majority of them got filtered out when using that 3-day old file. Well the first 4096 bytes worth of them.

This could be very useful for high ISO long exposures ... IF that file-length limit was more. My 64 second ISO 400 badpixel file is 136,138 bytes. The main reason being that the processing time is so much shorter, when compared to having to shoot a whole new frame at 64 seconds. You wouldn't have a 64 second delay between exposures and merging many frames wouldn't have those 64 second gaps between them.
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Offline LjL

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Re: Badpixel Mapping for Different Exposures
« Reply #41 on: 23 / July / 2008, 07:11:01 »
Wait, wait... you really can't use a badpixels list as a substitute for a dark frame.

Take a long dark frame and then push the histogram up so that the hot pixels get clipped, and you'll notice that there are patterns in that frame aside from the hot pixels themselves: you'll likely see, as I said, a blue glow in the top left corner, and also other less obvious artifacts that are at brightness levels close to random noise, but clearly aren't random noise.

Why can't you use a badpixels list to fix those? Well, two main reasons I can think of:
- both the original badpixels code and mine work, to an extent, by interpolating the bad pixel using the nearest neighbors. But if the neighbors are bad, too, then hmm...
- we could increase the 4096-characters limit to something higher, or even allocate memory dynamically to remove the limit altogether. But still, the bad pixels are stored in a linked list, each item being 96 bytes wide, so your 9634 pixels would take up 900 kilobytes, and that's more memory than my camera has.

All in all, if you want to obtain the effects of dark frame subtraction without taking a dark frame after each exposure, then just take one dark frame for each shutter speed, and then use those all the time.

It's also theoretically possible to take just one dark frame and simulate ones for other exposures using a bias frame.

The badpixels list just isn't a viable approach in comparison with the above methods.
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Offline vpamir

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Re: Badpixel Mapping for Different Exposures
« Reply #42 on: 06 / August / 2008, 15:35:20 »
Hi all,

I'm using allbest-s5is-101a-51-462 for my S5 and trying to figure out the hot-pixel removal feature. I tried the command line utility to make a couple of different "badpixel" files using a couple of treshold values but when i compare the two dng files (converted from chdk raw to dng) one of which i didn't use the removal feature and the other i used it, i don't see any difference. I especially hoped the most bright ones to dissapear but they didn't. Am i doing something wrong here or isn't this feature included in the version of CHDK firmware i'm using?

Thanks.
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Offline LjL

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Re: Badpixel Mapping for Different Exposures
« Reply #43 on: 12 / August / 2008, 09:55:25 »
Are you using the standard badpixels file, or the several files for different exposures as described in this thread? If you're using the latter, it won't work unless you download and apply the patch that I posted here.
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Offline mad_a720

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"BADPIXELS" directory
« Reply #44 on: 21 / August / 2008, 05:21:22 »
Hi, may be you can help me (I posted it elsewhere, but maybe in the wrong thread):

I wonder how I can create a "BADPIXELS" directory on my SD card (4 GB, FAT). Thanx to the plural there are now 9 letters instead of 8 (FAT !) and my cam seems to have problems to find this directory (listed as "BADPIX~1"). However, I didnt get it running.

mad.
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Offline dzsemx

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Re: Badpixel Mapping for Different Exposures
« Reply #45 on: 21 / August / 2008, 05:26:15 »
i think an automatic badpixel mapping should be the best, olympus (and probably others too) cameras have this feature
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Offline fe50

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Re: Badpixel Mapping for Different Exposures
« Reply #46 on: 21 / August / 2008, 06:19:52 »
Quote from: mad_a720 on 21 / August / 2008, 05:21:22
Hi, may be you can help me (I posted it elsewhere, but maybe in the wrong thread):

I wonder how I can create a "BADPIXELS" directory on my SD card (4 GB, FAT). Thanx to the plural there are now 9 letters instead of 8 (FAT !) and my cam seems to have problems to find this directory (listed as "BADPIX~1"). However, I didnt get it running.

This patch for A650 from LjL is NOT implemented in the trunk or in the Juciphox build, also it's NOT in any Autobuild - you'll get it only by compiling your own version by yourself, so then you can easily change the directory name in your source code...

*EDIT: edited the wikia article for Juciphox (MoreBest#Bad_Pixel_Removal).
« Last Edit: 21 / August / 2008, 06:32:07 by fe50 »
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Offline Sess

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Re: Badpixel Mapping for Different Exposures
« Reply #47 on: 04 / April / 2009, 20:57:03 »
Okay, time to revisit this. So the latest version of AllBest is 0.9.7-727. The patch file posted is the kind where you read it and find the lines listed and alter, add, and subtract as described, right? First, I've only once before used a patch file. Second, the patch file appears to be specific to AllBest 430. How do I get it working on 727?

Side question: If I have badpixel files for all the way up to 15, 30, or even 65 seconds, could I just turn off Dark Frame Subtraction? Don't they pretty much do the same thing?

Unrelated question (in case you happen to know off hand): I'm using a 16 GB card with the small 2 MB partition for booting. The latest builds of AllBest have DISKBOOT.BIN, PS.FI2, and vers.req. Obviously DISKBOOT.BIN needs to be in the 2 MB partition, but what about the other two?
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Offline tony22

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Re: Badpixel Mapping for Different Exposures
« Reply #48 on: 13 / August / 2010, 21:58:41 »
Sess, I read through this thread with some interest. I'm using the badpixel file for my JPEGs, but since there is only one I built it against a 1/10 sec shutter speed. That seemed to be a good break point. When I got much below that I started getting more and more warm pixels, but since I rarely shoot down that low I figured 1/10 sec was a good capture point.

I think the speed compensated badpixel routine is a great concept. I would go further to suggest also having variations for ISO compensated correction files. Since my G9 does its own dark frame correction at speeds of 1.3 sec and larger I figure I'd need up to maybe 10 files per ISO (or less) to cover the range of shutter speeds where it would be necessary.
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