Re: scaning suggetions from a viewer of our site...

Michael Maier (
Thu, 24 Aug 95 11:54:18 -0400

At 10:34 AM 8/24/95 -0400, rei@MIT.EDU wrote:
>I don't have any documentation pointers on this, but I hesitate to use
>jpeg format because I have heard (and I think I've seen) that it is a
>*lossy* format. That is, every time you load a jpeg image, it changes
>slightly. The colors change. If you compare a freshly-made jpeg with
>a jpeg that's been modified a few times, I think you'll find the
>colors have changed (even though you haven't touched them). GIF
>format does not have this problem. So it comes down to "You never
>want to edit a jpeg file" --- which can be a real pain.

Jpegs are _lossy_ in the sense that they through oput color info not
detecable by the eye. Opening an original jpeg each time doesn't cause
increased image loss (which is what happens when an image is loaded onto
a page). Opening it and then re-jpeging it can cause image loss. A way
to tell how the pixels have changed is save a copy of an original. Then open
and jpeg an image about 10 times. Then do a difference operation on the
the 2 images. THis will show you the amount of changed pixels.

Michael Maier