The Joy of Pixel Density

Started Jul 13, 2008 | Discussions thread
aclo Regular Member • Posts: 480
Re: Thanks John

chrswggl wrote:

Joesiv wrote:

Brad Nichol wrote:

On the subject of noise a method I often use with compacts under low
light is to take 4 or more identical exposures and blend them in
registration at 50% in photoshop, what is really obvious by this
method is that once you have about 4 images blended together the
shadow noise has pretty much been all cancelled out leaving just the
real picture information, so even with really high MP counts we could
get totally clean results if we needed it for some non moving
subjects.

Something that confuses me is, if you take 4 exposures, and those are
"canceling" each others' noise, why wouldn't you just take a 4 times
as long exposure, at a lower ISO? Wouldn't that result in the same
performance?

Nope, the camera heats up as the exposure drags on. This results in
more noise. Also, stacking pictures will average out the noise.
Taking only one will do nothing to get rid of it.

His point, though, is that the single exposure will be 4 times longer, so 4 times more light, so 1/2 the shot noise (which will also be the case for 4 averaged shots of 1/4 the duration of the single long one). Read noise is another story, though.

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ck3
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