Losing pixels

[rmo5]

I was told that each time you open downloaded pictures on the computer, some pixels are lost from the photos, therefore decreasing the quality of the pictures over time. Is this true? Is there a way to prevent this?

[dwterry]

It's not the act of opening the file that hurts the quality of it ... it's writing the file back out (over top of itself).

JPEG is termed a "lossy" compression. Meaning, it purposely throws away data in effort to reduce the size of the picture. Now... it does this in a manner which is supposed to not be noticeable (i.e. by throwing away what might appear to be "redundant" data within the image). But the more you do it, the more data gets thrown away.

So... if you're going to edit and re-edit an image, it's best to save it in a loss-less format such as TIFF or PSD (photoshop format).