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02-14-2008, 06:22 AM   #1
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Long exposure dead pixels..?

hi,

I've just picked my K100d back up form Jessops after being sent for a replacement ccd after noticing loads of dead/stuck pixels , bright blue/green mostly

Now it has come back its, its even worse , loads of hot pixels, and just as many stuck pixels as before

http://i173.photobucket.com/albums/w60/szbrozek/Pentax%20K100d/14thFeb08repaired_iso200_30s.jpg

This was at the lowest iso200@30s, but got the same image at 1/4000th at iso1600 both with the body cap on, no lens.

This is driving me mad..


any comments..

02-14-2008, 08:10 AM   #2
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is noise reduction on or off?

I have heard this can eliminate the problem.

also, shouldn't the service department map these, and exclude them. Somewhere I had read that it was possible.
02-14-2008, 01:19 PM   #3
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I would have thought so.. I was told by the Customer Service Dept at Pentax, that the CCD had been replaced, I suspect they didn't check it and change the excluded pixel mapping..

I did try searching for pixel mapping 'out' software to update camera firmware, but only found 1 piece of software for 1 particular camera..

Anyone know if the software to map out bad pixels on the K'series Dslrs is 'get' able.. I mean out the back door at Pentax
02-15-2008, 03:24 AM   #4
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Very strange,

I come to do some googling regarding pixel mapping, hot and stuck pixels ect..

I switched it back to Jpg mode, and took some at 250th/iso200 cold, and the same after leaving it on for a few minutes to warm all the circuits, nothing clean as a whistle..

Came across Michael Salzlechner's DeadPixelTest software, tried it out on a black/lens cap on photo, and behold, all those little hot pixels and even the stuck ones were not visible..?:S perplexed am I.. The software detected a possible 28 or so hot pixels (none visable), no stuck/dead pixels..



What concerns me is that at sometime those hot/stuck pixels will creep back into photos..

Anyone experienced this hot/stuck pixel dissapearing act.?


sz

02-15-2008, 04:53 AM   #5
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QuoteOriginally posted by szbrozek Quote
Very strange,

I come to do some googling regarding pixel mapping, hot and stuck pixels ect..

I switched it back to Jpg mode, and took some at 250th/iso200 cold, and the same after leaving it on for a few minutes to warm all the circuits, nothing clean as a whistle..

What concerns me is that at sometime those hot/stuck pixels will creep back into photos..
The temperature of the circuit/sensor has some minor effect on noise however exposure time is a far greater factor. Assuming that you have NR turned off the hot pixels should reappear in the same positions/colours if you make another 30 second exposure, probably even with the camera at 0 deg C. Stuck pixels remain visible regardless of the exposure time but hot pixels become brighter with exposure time. As the ISO is raised hot/stuck pixels become more noticeable.

For longer exposures (>=1 sec)when saving as jpg in camera it's best to leave NR turned on. The NR is a subtractive type, after the exposure is made the camera automatically makes a second exposure (with the shutter closed) for the same period of time and uses this second file as a subtractive mask.
02-15-2008, 09:08 AM   #6
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Ive just been comparing before and after repair pics, and the same hot/stuck pixels are there, in the same places.!! :angry: especially after being told the ccd was replaced.. I feel totally cheated, not sure I trust Pentax, maybe Canon or Nikon have better Customer Service..?

I've had a moan at them on the phone already, and told the usual, just send it back with a letter explaining the issues and the fact that this is a 2nd return for the same repair..

Maybe this time they will get the idea of a 'repair'..
02-15-2008, 01:38 PM   #7
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You can remove hot pixels in long exposures by turning NR on but be aware,the cam will make a dark frame exposure equivalent to the original exposure before subtracting it. Not so bad at 1 sec but at 30 secs or longer,it becomes a bit of an ordeal. An alternative is to shoot dark frames seperately and subtract them in software; just make sure NR is off if you do this. This guy nicely made a web page to explain the technique,he has also included info on making and utilising bias frames ash's "Diamonds from the Rough" Page
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