why are there red, blue, green dots in my photos?

Started Aug 27, 2004 | Discussions thread
Christopher Mann
New MemberPosts: 13
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Re: why are there red, blue, green dots in my photos?
In reply to hurstdog, Aug 28, 2004

Hurstdog, of all the answers I have recieved, yours is the only one I believe makes sense. I didn't know about "hot pixels". it was pretty hot in the plane. the exposures were merely one second. but I think your answer fits. I really do. thank you very much.

hurstdog wrote:

Christopher Mann wrote:

...

...
does anyone know what could have possibly caused these dots to appear?

How long were the exposures? Were you shooting a lot in a short
period of time when these appeared?

I think that most likely they are hot pixels. I get them when I
take shots of stars with my D70, if I turn on long exposure noise
reduction they go away though.

Its not x-rays, or other type of radiation, its blown channels
caused by pixels overheating. They're red, green, and blue because
thats the colors the blown pixels pick up.

For more info: http://www.imaging-resource.com/ARTS/HOT/HOT.HTM

Its something that every digital camera does to some degree,
especially with longer exposures and higher ISO's.

Here are two shots that demonstrate what in-camera noise reduction
can do, both taken from Lake Tahoe about a month ago, both over a
minute exposure with ISO 800+.

First, with no noise reduction, you might have to zoom in to see
the red, green, and blue pixels. Also, you'll notice a purple
cloud in the top right, because of the heat generated from the
camera's internal circuitry exposing the image.

With Long-Exposure NR turned on, it takes a dark frame of the same
length as the frame it just took, and subtracts it from the
previous frame to get rid of the noise. Here are the results (note
that this was taken from a different perspective, and about an hour
after the first shot):

Both of those should be a little blurry, I was still getting the
hang of manual focusing on the stars in those shots.

Hope that helps.
-Andrew

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