Does Downsampling Reduce Image Quality?

On Wed, 21 Dec 2005 22:26:54 -0600, Ken Hall
wrote:


I understand that upsampling can result in a poor quality image, but I
have always been under the impression that downsampling does not
reduce the image quality.

It's a little difficult to be sure this question is clear, so I'm
going to use the following hypothetical scenario.

Assume my printer cannot take advantage of resolutions greater than
300 ppi and that I have an image which is 1200 ppi.

If I downsample from 1200 ppi to 600 ppi and print it, will the image
be lower quality than if I had printed it at 1200 ppi?

If I downsample from 1200 ppi to 300 ppi and print it, will the image
be lower quality than if I had printed it at 1200 ppi?

Ken
If you print or display an image in a way that shows less pixels than
the image contains, it has to be "downsampled" somewhere. The
resulting quality depends somewhat the algorithm used to eliminate the
extra pixels that don't get printed or displayed. It can be as simple
as discarding some of the pixels, or it can be more sophisticated. The
downsampling can be done in several places including, but not
necessarily limited to, image editing software, a device driver, or an
operating system component.

In most cases, you will get more control and possibly better results
by making adjustments in your image editing software. You just have to
try various approaches and see what makes a difference to you.

Leonard