We all know the menu allows you to chose image size.
We all know the different sizes contain different amounts of megapixels.
But, how does it work? Is the camera using all the same pixels in the sensor regardless of how you set the size and then just compressing the image into fewer pixels to get a smaller size file? Or is the camera somehow using fewer pixels on the sensor in the first place as it captures the image?
Here is why I wonder what is going on. If the camera is using, for example, one fourth of the sensor pixels to capture a small size image why not "bin" four pixels together (combine their data into one) and thereby achieve the benefits of greater low light sensitivity which can be obtained from larger size pixels because now you have four times more light falling on one "binned" pixel?
If this were true a person could decrease noise at high ISO by switching to the small image size. Just an idea and wondered if it could work.