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badpixel file...."file is unknown" :(

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Offline gcgc

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Re: badpixel file...."file is unknown" :(
« Reply #10 on: 11 / June / 2014, 01:56:37 »
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Dark frame subtraction was not disabled, it was "auto" :(
I had to make the things again..... sorry if I wasted you're time :(
The result is the following

4 sec, iso 80

> dngload crw_0087.dng
loaded crw_0087.dng
> dnglistpixels -min=512 -fmt=chdk -out=badpixeliso80.txt
7 matching pixels
> dnghist -bin=256
0-255 15999010
256-511 23
512-767 0
768-1023 2
1024-1279 3
1280-1535 2
1536-1791 0
1792-2047 0
2048-2303 0
2304-2559 0
2560-2815 0
2816-3071 0
3072-3327 0
3328-3583 0
3584-3839 0
3840-4095 0

4 sec, iso 400

> dngload crw_0088.dng
loaded crw_0088.dng
> dnglistpixels -min=512 -fmt=chdk -out=badpixeliso400.txt
16 matching pixels
> dnghist -bin=256
0-255 15973637
256-511 25387
512-767 9
768-1023 0
1024-1279 0
1280-1535 0
1536-1791 0
1792-2047 0
2048-2303 0
2304-2559 0
2560-2815 0
2816-3071 0
3072-3327 0
3328-3583 0
3584-3839 0
3840-4095 7

4 sec, iso 800

> dngload crw_0089.dng
loaded crw_0089.dng
> dnglistpixels -min=512 -fmt=chdk -out=badpixeliso800.txt
923 matching pixels
> dnghist -bin=256
0-255 15139855
256-511 858262
512-767 878
768-1023 35
1024-1279 3
1280-1535 0
1536-1791 0
1792-2047 0
2048-2303 0
2304-2559 0
2560-2815 0
2816-3071 0
3072-3327 0
3328-3583 0
3584-3839 0
3840-4095 7

The result is a little different but luclky not so much (at least for the little knowledge I had  in these days) :)
At iso 400 the're the same 7 hot pixel (even if with higher values) plus 9 more but in the range 512-767, that could be, as you told me, the tail of the noise.
I know that for practical purpose it doesn't matter (only 9 pixel more!) but I'll ask you the same to know you opinion: I think the best choise will be to use the 80 iso badpixel, isn't it?

And just one more question so that I don't make wrong now at the end: have I enable again dark frame subtraction in camera "daily usage" ?

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Offline reyalp

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Re: badpixel file...."file is unknown" :(
« Reply #11 on: 11 / June / 2014, 16:42:45 »
Dark frame subtraction was not disabled, it was "auto" :(
The results are pretty similar, so I would guess your camera wasn't taking a dark frame with the 4 sec exposure anyway. If it was actually taking a dark frame before, there really shouldn't have been hot pixels. The results will vary some between shots and depending on sensor temperature.
Quote
And just one more question so that I don't make wrong now at the end: have I enable again dark frame subtraction in camera "daily usage" ?
If you want normal camera behavior, you should leave it in auto.

The Canon firmware will generally enable dark frame for exposures longer than a few seconds (the exact details vary some between models). When this happens you see "busy" for the same time as the exposure, so for a 5 second exposure, the actual shot would take 5 seconds, then the camera would be busy for 5 seconds. The "busy" time is the camera taking a second exposure with the mechanical shutter closed, and then subtracting it from the real image. This helps get rid of hot pixels and some other problems that happen with long exposures, see http://en.wikipedia.org/wiki/Dark-frame_subtraction

If you are shooting hand held, then your exposures will be shorter enough that the canon firmware doesn't use a dark frame.

If you are doing astrophotography or something like that, you might not want to wait for a dark frame between every shot. In that case, you can disable dark frame subtraction, and then make dark frames separately and subtract them when you process the images.
Don't forget what the H stands for.

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Offline gcgc

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Re: badpixel file...."file is unknown" :(
« Reply #12 on: 12 / June / 2014, 00:49:07 »
thanks, now everything is clear to me  :)

 

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