Lower resolutions

[cb2]

I have a PowerShot A80, 4 mega pixels.

When I choose a lower resolution in the FUNC. menu, exactly what happens with the camera....does it selectively "throw away" information recorded on the image sensor? It seems pressing the shutter ought to initially capture all 4 million (plus or minus) pixels, but then to reduce file size, something (in addition to compression) takes place. What, exactly, takes place?

Just curious....

[gtg]

The A80's sensor can capture 4 million pixels when it is in Large File mode.
When u select a lower resolution like for example a Medium mode, then the A80's sensor will be stripped down to capture only less pixels. (may be 3 milllion pixels. Since the number of pixels that is captured is less, the file size reduces.
This is what happens when a low resolution is selected.

Dont confuse this one with compression.
Because, there is another selection that can be done in the camera for JPEG settings like(Standard, Fine, SuperFine etc). This setting determines the quality of the image after compression. SuperFine mode will have the least compression and the best image quality whereas the Standard mode will have the most compression and least image quality.

Hope this explains

[Jon]

Actually, the "extra" pixels are thrown away during the in-camera processing. If you look at the available resolutions, and at the way sensors record (2 green cells for every red and blue cell), it'll become clearer. The resolutions don't have a straightforward relationship (2702x1704, 1600x1200, 1024x768, 640x480) so you can't just drop every nth sensor. Using just the specified number of cells from the center portion of the sensor would mean that the effective lens focal length would change at the different resolutions. So the processor takes the picture using full resolution and resamples the image as it's being processed. This is really quite similar to what happens when you use the resize/resample options in your photo-editing program.

[BOBinsane]

I'm with Jon the math man. "Throwing away" pixels will make a photo that is missing spots, and cameras do not have a method moving pixels closer together after that.