sensor pixels and image size

[garry71]

I'm probably on the wrong track with this, but here goes.

From what I've read, cramming more pixels onto a sensor can cause problems with image quality.
Would selecting a smaller image size in camera mean that non adjacent pixels are used on the sensor, thus helping with the image quality?

Thanks a lot
Garry

 

[StewartR]

Would selecting a smaller image size in camera mean that non adjacent pixels are used on the sensor, thus helping with the image quality?

No.

Selecting a smaller image size almost certainly does NOT use non-adjacent pixels on the sensor, for two reasons that I can think of:
(1) Smaller images aren't necessarily the right size for this to work. For example my Canon 40D has 3 resolutions: high = 3888 x 2592, medium = 2816 x 1880, and low = 1936 x 1288. The low resolution is clearly equivalent to using every other pixel, but the medium resolution is equivalent to using roughly (but not exactly) 3 out of every 4 in each row.
(2) The design of the Bayer filter means that you wouldn't get a proper mix of colours by using alternate pixels.

I suspect what's happening is that the camera is sort of averaging the outputs from several pixels to produce the smaller images.

You will get better IQ in one respect, which is that averaging the output from several pixels will reduce noise. But you'd get exactly the same result by downsizing the image in Photoshop.

 

[garry71]

Ok, thanks a lot Stewart

 

[maarten.dhaese]

Agree with the above. Selecting a smaller image size will not improve image quality, or at least not in the way that you expect.

When you take a picture, the camera will always use all the pixels on the sensor.

All the information from the sensor is then used to create a JPEG with a certain size via in-camera processing. If you select a smaller size, the same information is then used to create a smaller JPEG.

You can also choose to choose RAW, which means you keep all the information that was on the sensor when the picture was taken.

The exception to this would be a full frame (FX) Nikon that can also use DX lenses. If a DX lens is mounted on a full frame Nikon, the camera will only use the the pixels that are illuminated by the DX lens.