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View Full Version : Red spot (5x5 dots) on every photo (Canon 400D)


Zwiz
31st of August 2007 (Fri), 13:33
Hi everyone,

I've got a 5x5 pixels red spot always at the same place on every photo I take with my 400D. Is the sensor damaged? The camera is 2 months old only. It's not a lot of pixels but it is quite annoying to see it on every photo. Does Canon cover this kind of problem with the sensor?

Here a 400% crop of the red spot (1 pixel camera = 4 pixel on the screen). The white dot to the right is a single camera pixel added with Photoshop to serve as a reference.

Edited... I'm not sure anymore about the size of the spot. It could be a single pixel and the other pixels around could be affected by some kind of interpolation from the image algorithm. The faulty pixel is white when shooting something dark.

bildeb0rg
31st of August 2007 (Fri), 13:37
Must be worth a call to the techies...never seen it on mine, so I would say you have a problem

sheawyatt
31st of August 2007 (Fri), 13:43
It's just a cluster of hot pixels...I've got two of those spots (4 pixels each), but they only show at ISO's greater than 400 or with exposures longer than 15 sec. And when they do show, the auto noise-reduction in Aperture almost always takes them out. So they are a non-issue for me. Mine are in the corner of the frame though, if they were in the centre I might be more concerned.

DDan
31st of August 2007 (Fri), 13:45
Looks like a couple hot pixels. Put the lens cap on and activate manual sensor cleaning for 30 secs. Turn the camera off and back on to clear sensor clean mode. Take a test shot and report back. This has been reported to remap hot pixels on the 400D.

Zwiz
1st of September 2007 (Sat), 09:58
Looks like a couple hot pixels. Put the lens cap on and activate manual sensor cleaning for 30 secs. Turn the camera off and back on to clear sensor clean mode. Take a test shot and report back. This has been reported to remap hot pixels on the 400D.

Thanks everyone and specially to DDan! The method worked perfectly and the hot pixel is gone now. I would be curious to call a Canon service center and see if they would give me this "undocumented" operation. Sending back the camera just for a hot pixel would be very frustrating.

Just for the record: I presume that those hot pixels are mapped at the factory and that there is little chance that other will developped with time. From the first images I took with this camera, I could barely see this hot pixel. But after 2000 clicks, it has become fully white thus the concern.

DDan
1st of September 2007 (Sat), 10:44
Glad to help. Nice to hear another success story.

gjl711
1st of September 2007 (Sat), 13:56
Ya know, I wonder if it really remaps the pixel, or if it allows the pixel to return back to a base state. I have had these in the pas and last time I clearly marked where the pixel was by setting the brush to 1 and marking the location x-y in the info window. When I applied the remapping the hot pixel went away. More importantly, the pixel behaved normally in that it could change color. Removing both batteries should have cleared everything from the camera, but the hot pixel did not return. I am wondering if a transistor on the sensor is just stuck on and by applying the cap on procedure allows it to clear. Anyone have a pointer to some info on how Canon does it?

pwm2
1st of September 2007 (Sat), 14:08
The sensor has a Bayer pattern, where each pixel is either red. green or blue. Even a single damaged pixel in the sensor will result in the neighbour pixels being affected, since the camera forms the full RGB color by interpolating between neighbours.

If you send the camera in, they will just map the pixel as bad, to let the DSP know that it may not be used for the averaging. Instead of sending it in, you should be able to map it out yourself.