It comes down to pixel size. You can't take a thumbnail image of, say, 100 x100 pixels and blow it up to an 8 x10 size because there just isn't enough information in the image to print that large.
A 640 x 480 image will give you a decent 4x6 or 5x7 image suitable for printing but you can't get an 11x14 out of it because there just isn't enough information.
You can always start with a large image and print downward in size but you can't take a small image and print upwards in size.Can anyone advise me on how to change the size of digital pictures withouth changing the quality of them?
if you want to make them larger...
it's impossible.
if you want to make them smaller...
download a program called IrfanView (it's free). it works a lot better than, say, paint...
