Noise at lower resolutions (G7, specifically)

[philbond87]

I have no idea how this works, but perhaps someone here might.

Shooting at full resolution, the photo sites on a sensor are a certain size. (less than 2 microns for the G7, I believe I read). This smaller size seems to result in more noise in lower light situations.

Does anyone know if the noise characteristics are any different when the camera is set to less than it's maximum resolution?

Thanks.

[Henrik Paul]

Even though the camera has been set to take less than full resolution images from the menus, the image itself is most often (haven't heard of any other method yet) taken with the full sensor, and during the path from the sensor to the memory card, along with many other manipulation steps, the image is resized to its smaller size.

So yes, the image might seem a bit less noisy if taken as a smaller image, as each 'noise pixel' is sized down, but the image has to be made a whole lot smaller to effectively eliminate all noise when at its worst levels.

This applies to all digital cameras.

[philbond87]

Even though the camera has been set to take less than full resolution images from the menus, the image itself is most often (haven't heard of any other method yet) taken with the full sensor, and during the path from the sensor to the memory card, along with many other manipulation steps, the image is resized to its smaller size.

So yes, the image might seem a bit less noisy if taken as a smaller image, as each 'noise pixel' is sized down, but the image has to be made a whole lot smaller to effectively eliminate all noise when at its worst levels.

This applies to all digital cameras.
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Thanks Paul.

So I am to understand that the image is captured just as though it were using max resolution then sized down - rather than having the sensor devote more "photo sites" to fewer overall "pixels."

Any apparent reduction in noise is simply due to the fact that everything has been rendered smaller... including the noise.

Correct?

[Henrik Paul]

That's exactly right.

The reason for not devoting more photosites per pixel on lower resolutions is the Bayer Matrix/Filter/Sensor (many names for a loved child) - more information can be read at http://en.wikipedia.org/wiki/Bayer_filter - but the point is that each photosite has a dedicated color it is sensitive for, and neighboring photosites can't be used to add up size, as no neighboring photosites are sensitive to the same color.

The Foveon X3 sensor (used by Sigma) has a different approach, where each RGB-photosite is beneath each other. Therefore, in theory, it could be possible to dedicate several photosites per pixel inside the camera. Alas, that can also be done manually in any image processing program that can resize images, so there is not much point.