I've noticed that some cameras list both ccd resolution and image resolution. What is the difference between these two?

-- Lance Gardner (lanceg@iswt.com), May 14, 1998

Answers

The CCD resolution will be slightly bigger than the finished image resolution. The excess pixels around the border are covered and used to determine the black level of the image.

-- Ben Jackson (ben@ben.com), June 17, 1998.

You want the CCD res to be bigger than the image res, but that's not always what you get. Some cameras have significantly less CCD res than the image res and interpolate pixel data from the CCD to fill in the blanks.

Kodak is one company that I've noticed always has a better CCD res than image res. I'm sure there are others.

Stay away from cheap models that say 1280x960 output for $400 when the CCD is much less than 1280x960.

-- Steve Durgin (durgins@prodigy.net), June 26, 1998.

Just to correct the previous response, Kodak is the only manufacturer notorious for using a smaller CCD than the output resolution of the camera (the DC120 used a 800k pixel sensor with non-square pixels and interpolated the resolution to 1280x960, claiming to be a megapixel camera).

The other notable cameras which advertise output resolution higher than sensor size are the Agfa line. They claim the magic is in their postprocessing software which resamples the image to a larger size. At least some of the magic comes from compressing the image less when it's taken on the camera.

Of course no one-shot digital cameras actually have full RGB info for every pixel, most have 2 green and 1 each of red and blue pixels in every group of four, and each color plane is resampled to the final resolution. This can result in color aliasing around highlights, but mostly it goes unnoticed because it parallels a similar subsampling done during JPEG compression. But this does explain why a 640x480 image from a 1280x960 shot looks better than the same shot taken by a 640x480 camera...

-- Ben Jackson (ben@ben.com), August 16, 1998.