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B1ue Jan 22, 2006 1:15 PM

1 Attachment(s)
One of the main reasons I got the 5D was for low light and night photography. I've been taking night shots, experimenting with 800 and 1600 ISO. In general, I don't like the way in-camera NR softens pictures. I turned off noise reduction and the photos had predictable random noise, but I also found clusters of hot pixels in four places. They appear in the same places in all night photos.

I tried some test shots with the lens cap on, all at lower ISO. Various combinations such as 200 ISO, 1 second, f3.5. 80 ISO, 10 seconds, f5.6. Tried longer exposures which resulted in lots of noise and a wash of magenta in the upper left corner in addition to the hot pixels. All the test shots were with JPEGs, fine or extra fine.

There are 9-12 hot pixels in each cluster. Is this reasonable for a one second exposure? My feeling is that these hot pixels are excessive. Attached is a screenshot crop from PS @ 600%.

BTW, when I do the lens cap tests with NR on, everything is black.

B1ue Jan 22, 2006 1:18 PM

1 Attachment(s)
Lens cap test, screenshot crop from PS @ 600%.

kassandro Jan 22, 2006 1:55 PM

With long exposure times nearly all cameras exhibit dead pixels. If you don't like the in camera noise reduction, you should use the raw mode. You can then remove the dead pixels rather easily. If you use jpeg, then a dead pixels propagates to neighbouring pixels and the complete removal of the dead pixel is fairly difficult.

B1ue Jan 22, 2006 2:47 PM

kassandro, I know what you mean about JPEG anti-aliasing. I'll shoot some RAW tests. I don't think these are dead pixels because I don't see them in daylight or flash pictures.

kassandro Jan 22, 2006 3:52 PM

Yes, if I would see a truely dead pixel, which is also visible in day light pixtures, then I would send the camera to the manufacturer for repair if it is still under warranty.
Actually I wrote an Avisynth filter for a Canon Camcorder with an absolutely dead pixel. Because of the low resolution of camcorders such a dead pixel really looks ugly. Also, for camcorders you can't avoid compression. In this case the dead pixel did spread even to neighbours with distance 3. Thus in this case satisfactory dead pixel removal was very delicate. On the other hand, for raw pictures dead pixel removal is child's play. However, it has to be done BEFORE demosaicing. If you do it after demosaicing, the dead pixel again spreads to its neighbours, though usually only to neighbours with distance 1. With DCraw you must make a dead pixel file and then these dead pixels are removed before demosaicing by DCraw.
Looking at your two pictures, I am quite sure that you have only a single dead pixel, which spreads to its neighbours through compression and demosaicing.

B1ue Jan 22, 2006 4:08 PM

Appreciate your feedback, kassandro. Three of the problem areas are in the upper third of my photos, putting them in the sky area of night shots where they're very noticeable. Easy to find and fix, but still a nuisance. So, for a new camera, what do you think is an acceptable number of hot pixels to have? For example, in a 1 second exposure, ISO 100? Thanks.

kassandro Jan 22, 2006 4:27 PM

I made night shots with two cameras a Canon A70 and a Ricoh Caplio GX. Both showed several dead pixels with long exposure times. I haven't yet made night shots with my current two cameras, a Canon S1 IS and a Nikon 8400. Now, a DSLR has much larger pixels than P&S cameras, whence the signal quality of such DSLR sensors is much better and hot or dead pixels should occur less. Personally, I would wait for some months. If the hot pixels increase all time or show up even under normal light, then I would return it, otherwise I would consider it as acceptable. I am looking forward to buy a KM 5D or 7D this year, mainly for low light and sports. It would be nice to know how often hot pixels of the above type are for the KM 5D.

bernabeu Jan 23, 2006 9:04 PM

change the date in the camera to 60 days ahead, take a few shots, put the date back

the camera (i think with 95% certainty) will 'remap away' the hot pixels

JimC ???????????????????????????

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