Stuck Pixels in Low Light at DVinfo.net

John Wheaton · May 5th, 2007, 08:38 AM

Hey guys I'm kind've going crazy over something that I'm not sure is a huge issue or not. I'm on my 3rd XH-A1 camera and all have exhibited stuck pixels in the recorded image (on the CCD?). This is really only visible occasionally when shooting in really low light, say +12 gain. It becomes more obvious if used in conjunction w/ slow shutter speed, i.e. 1/30. All the cameras i've tested had at least 1 or 2 light gray-green, stuck pixels. A good test is to turn the camera on w/ the lens cap attached, and as the camera warms up over a few hours see if you notice anything while viewing on a high def monitor.

The weird thing is it's kind of intermittent. They seem to fade in over time as the camera warms up, but will then disappear if the camera is turned off briefly, then turned on again.

In everyday use in bright lighting, they are never visible (w/ say 0 gain) so I'm thinking of just living with the issue. What do you think?

Don Palomaki · May 5th, 2007, 09:51 AM

That is a typical behavior of CCDs. All pixels have a "dark current," a type of electrical charge leakage. Some pixels will have more than others as a result of minute manufacturing differences as the CCD are formed in the chip foundry, and the level can vary with temperature as well. As far as the rest of the electronics are concerned, there is no difference between this dark current and the current caused by light hitting the pixel. As you increase the gain (or exposure time), the dark current is amplified and can become apparent in the image if image conditions are right (e.g., a very dark image).

Consider NTSC black is 7.5 IRE.
A pixel evaluating to 5 IRE output would black.
Add 12 dB gain and that pixel becomes 20 IRE well into the visible range.
Similarly, if you double exposure time, you accumulate dark current twice as long (the same as adding 6 dB gain) and now you have 40 IRE.

Its a problem if it effects your normal shooting.

John Wheaton · May 5th, 2007, 11:07 AM

Thanks for the response Dan. Actually it really doesn't affect shooting in most circumstances (i.e. 0 gain, normal light conditions). Only once did I notice it in recorded footage, and the camera was at +12 gain, 1/30 shutter in a really dark room. I was just shooting test footage and normally would have more available light..

Otherwise a great camera and I will probably keep this one - it's really my extreme ocd that caused me to obsess over this issue! :)

May 5th, 2007, 08:38 AM	#1
John Wheaton Tourist Join Date: Mar 2007 Location: Burbank, CA Posts: 2	Stuck Pixels in Low Light Hey guys I'm kind've going crazy over something that I'm not sure is a huge issue or not. I'm on my 3rd XH-A1 camera and all have exhibited stuck pixels in the recorded image (on the CCD?). This is really only visible occasionally when shooting in really low light, say +12 gain. It becomes more obvious if used in conjunction w/ slow shutter speed, i.e. 1/30. All the cameras i've tested had at least 1 or 2 light gray-green, stuck pixels. A good test is to turn the camera on w/ the lens cap attached, and as the camera warms up over a few hours see if you notice anything while viewing on a high def monitor. The weird thing is it's kind of intermittent. They seem to fade in over time as the camera warms up, but will then disappear if the camera is turned off briefly, then turned on again. In everyday use in bright lighting, they are never visible (w/ say 0 gain) so I'm thinking of just living with the issue. What do you think?

May 5th, 2007, 09:51 AM	#2
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	That is a typical behavior of CCDs. All pixels have a "dark current," a type of electrical charge leakage. Some pixels will have more than others as a result of minute manufacturing differences as the CCD are formed in the chip foundry, and the level can vary with temperature as well. As far as the rest of the electronics are concerned, there is no difference between this dark current and the current caused by light hitting the pixel. As you increase the gain (or exposure time), the dark current is amplified and can become apparent in the image if image conditions are right (e.g., a very dark image). Consider NTSC black is 7.5 IRE. A pixel evaluating to 5 IRE output would black. Add 12 dB gain and that pixel becomes 20 IRE well into the visible range. Similarly, if you double exposure time, you accumulate dark current twice as long (the same as adding 6 dB gain) and now you have 40 IRE. Its a problem if it effects your normal shooting. __________________ dpalomaki@dspalomaki.com

May 5th, 2007, 11:07 AM	#3
John Wheaton Tourist Join Date: Mar 2007 Location: Burbank, CA Posts: 2	Thanks for the response Dan. Actually it really doesn't affect shooting in most circumstances (i.e. 0 gain, normal light conditions). Only once did I notice it in recorded footage, and the camera was at +12 gain, 1/30 shutter in a really dark room. I was just shooting test footage and normally would have more available light.. Otherwise a great camera and I will probably keep this one - it's really my extreme ocd that caused me to obsess over this issue! :)