5 megapixels from a 10 megapixel senor

[Foot]

What happens to the extra capacity in a 10 megpixel (photosites) when one sets the exposure to 5 megapixels? Are more photosites recruited to each "pixel" or is the extra capacity simply wasted?
Foot

[SmartWombat]

Pass.
It could be done in many ways.
What camera are you asking about?

[Foot]

Olympus e510

[mn shutterbug]

That is a deep question.

[Medley]

I would guess that the image is rendered at 10mp, then downsampled. I say that because that would seem to be the easier of the two methods for the manufacturer to use, but it;s really only a guess.

If you have photoshop, you could try this experiment:

Set the camera on a tripod and take two identical exposures- one at 10mp, and the other at 5mp. Open the 10mp image in photoshop, and downsample it to the exact same size as the 5mp image. Then place the two images on top of one another (it realy doesn't matter which image you place on top). Set the blend mode of the top layer to "Difference". Next, select the "Move" tool and use the arrow keys to align the images as much as possible (even with the tripod, the two images could be a few pixels off). in aligning the images, the object is to make the image as black as possible.

In the best of all possible worlds, the image will be completely black. This would indicate that the two layers are identical. In that case, you could say definitavely that the image is downsampled in the camera.

My theory is that you will either get light areas around the edges of the image, or wider grey images throughout the image. Light areas around the edges would likely mean that the image is downsampled, and the difference is in the sharpening algorithms. Wider grey areas would indicate that the colors are somewhat different, indicating a change in the sampling of the sensor.

Either way, you can compare the images to see if shooting in the smaller file format provides any benefits.

Hope this helps some.

- Joe U.

[Foot]

Many thanks Joe U. Your note is most helpful.
Foot