I get questions about image formats all the time, so if you don’t know your JPEG’s from your GIF’s, this is for you. First, a little background on file compression.
There are basically two ways of saving images, lossy or lossless (no, I didn’t make those up). If an image is saved in a lossy image format, it means the format being used discards some of the “unimportant” image information. However, the resulting image file is smaller. Lossless retains ALL the image information.
OK, now that you know that, here’s a overview of the most common image formats.
JPEG – By far one of the most common image formats. It’s primarily used for photographs. It is a lossy type of format, but most people can’t really see the difference. You can adjust the amount of compression when saving a JPEG image, so you do have some control over the final output quality. JPEG’s are extremely popular since they compress into a small file size and retain excellent image quality.
Keep in mind that the more you compress a JPEG, the more “pixely” it will tend to look. For the best results, save your JPEG’s at the “medium” or “high” setting (your imaging software should bring up this option when you go to save as a JPEG). I really can’t see any image degradation in most pictures saved at the medium setting.
GIF – Another popular format, especially on the web. It’s a lossless format that’s ideal for graphics. GIF’s can be either static or animated. If you’ve ever seen a graphic on a web page that was animated, you’ve seen one of these animated GIF’s. Most of the time GIF’s are used for non-photographic type images (buttons, borders, stuff like that).
BMP – Back in the day, this was the standard Windows image format. It’s lossless, and works well for pictures or graphics. It’s an uncompressed file format, though, so it takes up lots of disk space.
PNG (Portable Network Graphic) is a lossless image format, properly pronounced “ping”. It was designed to replace the older and simpler GIF format. Like GIF, you can make transparent images for buttons and icons, but it does not support animation. A PNG file can generally end up being twice the size of a JPG, three times larger than a GIF – and some browsers, such as older versions of Internet Explorer, incorrectly rendered.
TIFF – My favorite. It’s a lossless format that can use file compression (called LZW compression). It won’t result in as small a file as a JPEG (which is why it’s not used on the web), but you do retain all image quality. When compressed, the file is usually about half the size of the original file. I normally save photos I’m archiving in this format. I can then convert them to other formats for screen savers, wallpaper, or web images.