I don't understand how the file size and image quality are related when I save a photo. For example, I can start with a photo that's 4 megabytes, but when I save it at the highest quality level, it ends up even bigger--5 megabytes. How is that even possible?--Dennis Westlin, Jacksonville, Florida

It's magic, Dennis.

Seriously, it is a little confusing, because of the way that the JPEG file format works. In general terms, JPEG files keep track of the difference in the color between adjacent pixels. when you save a JPEG at a lower quality level, it throws away some of this color information in order to create a smaller file size, which can lead to color "fringing." (The resolution, or number of pixels in the photo, is never affected by the quality setting.)

So it's obvious that if you save a photo with a lower quality, the image size should go down. But if you start with a lower quality image and then save it with higher quality settings, the program saves detailed information about color transitions between pixels even if those color transitions don't really exist--and that can artificially inflate the file size.

Here's an example of how that works in real life: Your digital camera is probably set at the factory to save its photos at a medium quality level. If you later edit that photo on your PC and save it at the highest quality level, you'll end up making the file bigger.