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Old Jan 1, 2008, 3:40 PM   #1
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I've run about 500 pictures through my D40x and till last night I was very happy with it. Last night I noticed something strange in 3 of the pictures (out of probably 75).



Check out the attached picture, it is 3 crops taken out of the 3 pictures and zoomed to 2x the original size showing something. I don't really know what it is. The middle one could I suppose be some light getting though the hair in the foreground causing the shadow on the wall, but if it is it's weird that it's that sharp and greenish/blue when the wall is grey. The others are clearly little blocks of pixels which don't appear to be something actually in the picture.



All the shots do have quite a bit in common, the same room/lighting, shot in the child mode (I was chasing my 3y/o niece around last night, though 2 of them were on something besides her or next to her), they were all in max resolution, fine mode shot with the camera turned (portrait orientation). They are not even close to the same spot, but they can be described in the same general area (the upper right of the picture, near the center before they were rotated, upper left once they were rotated so the subject matter was upright). I don't know about the first one for sure, but I did notice the second 2 before I rotated the originals. At roughly 500 shots my first battery charge is showing that it's starting to discharge some.



Anyone see something like this before and/or know what's going on?
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Old Jan 1, 2008, 10:14 PM   #2
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Hi, I have seen something that looked a lot like this before.

It worked out to be a dead pixel (terminology???) on the sensor.

I'm sure that one of the top guys who run the forums will answer with a better diagnosis than mine.

I'm not that hip to a lot of the failures of digicams, but thought I'd maybe just throw that out. Just looks a lot like my pics were coming out.

Good luck with the detective work.


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Old Jan 1, 2008, 10:26 PM   #3
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I was wondering about that, but I sort of ruled that out since it's pretty clearly more then a pixle across in the pictures and they are not in the same location, though I guess I could be wrong.

I've gone through the rest of the pictures that I've taken and I don't see any signs of anything similar in the rest of the pictures.

If it is something wrong with the camera I'd like to figure it out while the camera is still new so I can replace it.

-mmp

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Old Jan 5, 2008, 6:10 PM   #4
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Ok, I have tons of views but no comments/help... common guys and girls, someone has to know what is going on here or how to figure it out.
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Old Jan 5, 2008, 9:32 PM   #5
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Yes, it appears to be a dead pixel. Perhaps you should reach for the clonning tool.

Sarah Joyce
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Old Jan 6, 2008, 2:08 AM   #6
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Sarah, the reason that I'm wondering about it is that it is in 3 different locations in the pictures, it's not the same point 3x.

Based on a little research that I've done it looks like it's not that uncommon, but that the software is supposed to eliminate it from showing up in pictures, so seeing it is uncommon unless you've got a lot of them or something is wrong.

I'm not worried about those pictures, like you said, the clone tool is easy enough to use to fix them.

What I am worried about is confirming that I have a problem and then I might as well get the camera replaced if I do have a problem since it's new.

I've shot dozens of random pics tonight trying to reproduce the problem, but haven't seen it again yet. Is there some good (preferably easy) way to confirm what the problem is? Maybe I'll play with some raw pictures trying to keep solid colors in those areas to see if I can see anything (if I can figure out what software will let me play with the raw images)


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Old Jan 6, 2008, 4:07 AM   #7
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Ok, I tried the procedure for finding dead and hot pixels here:

http://www.gdargaud.net/Hack/DeadPixels.html

I tried a number of shutter speeds between 1/4000 and 20s and there is only one spot, in the bottom right corner (nowhere near any of the green spots) that I think I can identify a messed up pixel. I did get some noise (4 spots) in the really long exposure picture but I think it might actually be light leaking in since they didn't show up anywhere else.

After seeing how hard it is to find these things even with a perfect nothing picture with edge enhancement I'm sure that whatever my green spot is its not a messed up pixel. After seeing what it looks like, I don't think that I could find the one that I'm pretty sure is messed up in a real, raw picture, and normally I'm pretty sure that between noise reduction and jpg compression that it wouldn't exist in an actual picture anyway

That makes me a little less nervous about having a camera problem, but now I'm even more stumped what my green spot actually is.


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Old Jan 6, 2008, 6:43 AM   #8
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mpikas-

I am glad to hear that you are more at peace with the dead pixel issue, and that you have now determined that it is indeed in a single spot. Thanks for sharing the problem and the possible solutions with us.

Sarah Joyce
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Old Jan 6, 2008, 8:32 AM   #9
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I'd try cleaning the sensor, normally dirt on the sensor shows up as a dark spot but it could be that you've got something in there that is semi transparent.

Ken
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Old Jan 6, 2008, 12:52 PM   #10
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I figured that at this point I can actually contribute something that will help someone else, so here it is... This is what you're looking for when you're looking for a dead or hot/stuck pixel. These are both cropped out of a screen shot of one of my raw images, converted to TIFF an open in an old copy of PSP. I included the overview bit so you can see that I'm at 100% zoom and where it is in the picture.

The first one is the stuck pixel as it actually appears in the picture. (yes, it's there, zoom in on it and it's easier to find. If you can't find it, take a look at the second one, it's EXACTLY the same picture with the "trace edges" edge enhancement applied to it to draw a box around the lonely pixel. Like I said, I don't see how you'd find this in a real picture or how it would get past both noise reduction and jpg conversion.
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