Picture File Formats

[Mike]

Here's a quick & dirty explanation for anyone not familiar with the most commonly used file formats on the internet.

.jpg is a file format using what is called "lossy compression". There's an algorithm that compresses the data, but depending on how much it's compressed, the quality of the pic will suffer. Quality is usually selected when you're saving a file off as a jpg, on a scale of 1 to 10 (usually), where 1 is the worst and 10 is the best. Let me illustrate with a couple of versions of the same pic.

This one is saved at high quality and uses 26kb - nice & crisp.

This one saved at medium quality using just over 6kb, and you can see the image is starting to suffer slightly from "digital artifacts", where the compression is actually losing information in the picture.

This one is saved at low quality and uses only 4kb, but the digital artifacts are all over the place, and the image is too damaged to use by any self-respecting webnaut.

I usually save my jpgs as medium quality for the web, as it saves space without much in the way of degradation of image quality. Most people won't notice much difference on casual viewing.

.gif is a file format used by Compuserve in the olden days of the internet (back in the 90s!), and could only display 256 colors. It was a product of its time, as most computers could only manage the same. It's still in use today, mostly for its ability to carry animations. Our smileys are .gif formatted files. To give the impression of more than 256 colors however, gifs can be encoded with "dithering", which creates the illusion of full color images. Have a close look at the logo below, and you'll see what I mean. The effectiveness of dithering varies depending on the subject matter. Pictures with a low color count can look pretty good, but pictures with a nigh color count & lots of gradation of tones will look rubbish! The gif doesn't save as much space as a medium quality jpg though, and this image uses up just over 11kb, which explains why jpg is taking over.

How you edit & save your pics is down to you and what graphical package you have/use, but at least now when a dialog box pops up with your options, you'll have a clue what they are!

HTH