Ask Dave Taylor: Tech and Business


JPEG considered a "lossy" graphics format?

I'm just starting out in the Web world and was just told by someone else who I respect that I should be careful with the JPEG graphics format because it's "lossy". I have no idea what that means, however. Can you enlighten me?

While I'm a big fan of the JPEG graphics format myself - just about every screenshot on Ask Dave Taylor is in JPEG format - I know exactly what your friend is talking about. A lossy graphics format is one where a small amount of information about the original picture is lost each time the image is saved.

To understand why that happens, it's critical that you know that the Joint Photographic Experts Group "JPEG" format uses a compression algorithm to try and shrink down the resultant image file size. You can see this quite easily by creating a 100x100 pixel solid black image then saving it as a JPEG. It'll be amazingly small considering that it's actually holding information on 10,000 different individual pixels or dots of information (on my Mac, it's only 823 bytes in size).

The specific compression that JPEG uses is...