Thread: Pixel Question
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Old Nov 5, 2004, 10:38 AM   #5
JimC
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Join Date: Jun 2003
Location: Savannah, GA (USA)
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José A. wrote:
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Ok, just a question:

First of all, the focal length of the lenses is related to the sensor size, right? So, if when you use different resolution settings (I own a Lumix FZ10) the focal length stays the same... that should mean you're using the whole sensor for less megapixels in the lowest resolutions.

Now, they say that having toomanymegapixelsinasmallsensor is one of the reasons for noise. If the above is true, shouldn't you have less noise when using a lesser resolution?


Am I just very confused? Should I recheck howstuffworks.com? (And yes, I'm gonna make the test)
The reason you have higher noise when manufacturers put more megapixels into the same size sensor is because the photosites for each pixel are smaller. As a result, when light hits them, they generate a weaker signal (requiring more amplification of the signal for equivalent sensitivity to light). This amplification also amplifies noise (like turning up the volume on a weak radio station, only you get image noise instead of static, hiss and hum).

If you use less of these photosites, this won't eliminate the problem (the size of the photosites is still the same).

Depending on how the manufacturer implements downsizing of images, they may be using a subset of the available pixels, or they may be interpolating so that the resulting pixel set is an average of values found in adjacent pixels (more likely).

But, you can do the same thing using software later if smaller viewing sizes are needed. When you view images using software that supports smaller viewing sizes, it's going to be averaging the values from adjacent pixels anyway. This does tend to make noise "blend in" more. Ditto for when printing at smaller sizes.

You're better off shooting in full resolution, and letting the viewing/printing software handle the downsizing part (if you even need downsizing for what you are doing).

I see no benefit to actually shooting in a lower resolution mode for noise reduction purposes. You are better off shooting in full resolution mode, then using software to reduce noise later if it's a problem (and good noise reduction software would use more sophisticated techniques to eliminate noise -- rather than simply downsizing an image).
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