Colored Specks from high ISO


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Crappinni

New Member
Aug 31, 2007
179
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Singapore
#1
Hello guys,

I recently discovered a small problem. I took a couple of test shots without a lens and with the mount cap on (therefore complete darkness) with varying ISOs (RAW, manual mode, everything else constant). I found that at higher (3200) ISOs, obvious green/blue specks appear but at lower (50, 100) ISOs, they're non-existent/very small. Oddly, when I compress it to JPEG, the spots become extremely difficult to spot so no picture is included.

Any idea what the problem is?
 

CS TAN

Senior Member
Sep 3, 2007
3,663
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Hong Kong
#2
Hot pixels.

This is very common with digital sensors. Really depends on your luck as some camera will have less and some will have more. If the hot pixels bunched up together in one place, perhaps you can go to service center for them to take a look at. If it scatters around, it should not affect picture quality in most cases.
 

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Crappinni

New Member
Aug 31, 2007
179
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Singapore
#3
Thanks for the quick response. That's pretty sad. I never noticed them until recently so is it possible that the condition deteriorates? I've always discriminated my photos to the pixel and never saw anything.
 

Rashkae

Senior Member
Nov 28, 2005
19,105
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#5
Also, it's high ISO noise. It's normal. When you shoot as JPEG, the camera tries to clean up some of the noise.

Since you're a pixel-peeper, I suggest never shooting above 200 ISO.
 

Crappinni

New Member
Aug 31, 2007
179
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Singapore
#6
Thanks! I only started shooting long exposure quite recently (acquired a decent tripod). I realise I can enable long exposure noise reduction which solves the problem too (each shot takes longer to process though).
 

IsenGrim

New Member
Jan 28, 2008
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#7
usually negligible.

but if the weather is warm, or your camera is hot due to usage (20 x 4min exposure with 1min interval on a warm night), these hot pixels can appear more frequently.

unless you are super anal about it. there are softwares to "subtract" these hotpixels from your images. these methods are commonly used in astro photography.
 

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