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Old Sep 1, 2010, 11:36 AM   #1
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Default Noise or something else...

I'm pretty happy with the results from my FZ38 and understand that due to the smaller sensor size compared to a DSLR I should expect more noise even in good light at ISO 80 and while the images are very nice for normal use, the noise does become enhanced when I use them for psuedo HDR work.

However, it occured to me that maybe what I'm seeing isn't entirely noise (which should be random) and might be down to engineering tolerances when trying to squeeze so many more pixels into a smaller space (which would be a more constant effect - like a 'hot' pixel). So I did a test and I'm interested in the results but not entirely sure what they mean.

My test was to take 16 black frames in RAW mode. Because you can't physically keep the lens cap on when you take a picture on the FZ38 I instead pressed the lens into the soft fabric inside the bottom of my camera bag. I think this is a reasonable approach and indeed most of the pixels come out completely black. But not all.

Next I multiplied each pixel by 64 so that the non-black pixels became visible. Then I averaged all 16 frames. If the non-black pixels are noise then they should be in different positions each time and would average out to close to zero. If they're something else they will remain. And lo and behold they're still there after averaging the 16 shots and some of the structures are quite striking. Here are a few 800% crops:

Note that these aren't what I'd consider 'hot' pixels and I had to multiple them by 64 to make them visible. I think they're a larger. more structured 'imperfection' in the sensor.

What I'm suggesting is that it is not the physical size of the pixels in a 1/2.33 sensor that are causing the 'noise' problems but the variance. It raises the possibility that a pp correction can be made to improve the results.
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Old Sep 1, 2010, 9:21 PM   #2
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'Hot' pixels will only normally show up in very dark areas anyway. A 'stuck' pixel, is one which is always on (or off) in every frame. You are demonstrating 'warm' pixels - those which don't get completely zeroed out when the sensor is reset prior to taking the picture. They do tend to be, as you demonstrate, relatively fixed, which is one of the reasons many cameras will do a dark frame subtraction for long exposures, where the light level is assumed to be very low, and the 'hot' or 'warm' pixels show up.

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