GIF and JPEG (JPG) image formats are different. You should know which to use when. Here are some examples.
Page "gifvsjpeg" last modified: 30Jun99

There are different types of image files. You'll get the best results if you know which type to use when.

Web browsers mainly support two different image formats: GIF (pronounced "Jiff") and JPG (also known as JPEG, and pronounced "JAY-peg"). These formats refer to methods for compressing the information that describes the images.

GIF is best for images that have solid colors, text, and line art. It is good for computer-generated images, such as those produced by a drawing program like Corel Draw. It is also best when the image has detail, like text, where every pixel (dot on the screen) counts. It does well with images that are made up of a limited number of colors. It does not compress photographs very well, especially images that show texture or color gradations, or that are 24-bit color. GIF is a "lossless" form of compression. Every pixel in the original image is preserved. GIFs are rarely used for large images on web pages because the benefits of no-loss are not visible to all but the most technical of viewers, but the huge differences in file size, and therefore download time, are noticeable to all.

JPG is best for photographs, and scanned photographs, of natural images. JPG gets its good compression by doing approximations, and is not as good for images where every pixel counts, or when you can get compression by using less than 24-bit color. It is usually a "lossy" compression, where you do not get back every pixel exactly as it was in the original image. There are different levels of JPG compression, ranging from little loss of detail and poor compression ("higher quality") to possible loss of detail with great compression ("lower quality"). On web sites, it's often best to use the greater compression, even if it means loss of detail ("lower quality") because it saves download time. The software you use to edit or scan your images often has a setting to control the JPG quality. You can always link the low quality image to another page with a higher quality, perhaps larger, image for people who want to print out as good a copy as possible.

Here are some examples to help you choose between the GIF and JPG formats:

GIF is better for solid colors, exact detail, and small text. JPG may lose the details and is often bigger.
1,542 bytes
Solid colors and lines GIF
GIF enlarged detail
Enlarged detail
This is an example of using a GIF for line art. It is compressed well and rendered well.
5,433 bytes
Solid colors and lines JPG
JPG enlarged detail
Enlarged detail
This is an example of using a JPG inappropriately for line art. Note the loss of detail and poor compression.
JPG is better for photographs. The same picture as a GIF will probably be bigger (therefore take longer to load in a browser) and look no better or worse.
30,327 bytes

About 10 seconds to load @28.8
GIF photograph of an inn This is an example of using a GIF for a photograph. Note the poor compression (almost 2 times bigger than the JPG), and 8-bit 256-color image.
15,996 bytes

About 6 seconds to load @28.8

JPG photograph of an inn
This is an example of using a JPG for the same photograph. Note the good compression and 24-bit, full-color image. (You will see the color difference best on a PC with a video card displaying more than 256 colors).
13,534 bytes

About 5 seconds to load @28.8
GIF photograph of sky and hills This is a more extreme comparison of GIF vs. JPG for a photograph. Note how much more storage space is taken up by the GIF.
5,822 bytes

About 2 seconds to load @28.8
JPG photograph of sky and hills Images like this, with color gradations, show off the benefits of using a JPG. The GIF is 2.3X bigger and looks worse than this JPG.
Use the lower quality settings for JPG compression. The added detail you get with high quality compression will not be noticeable on web pages, but the larger file size will slow loading substantially.
High Quality JPG
29,816 bytes

About 10 seconds to load @28.8
High quality JPG of electrical parts This is a JPG compressed with high quality (low loss) compression.  Note how much more storage space it takes up than the next image.

Here is an enlarged detail:
Enlarged high quality JPG
Low Quality JPG
10,939 bytes

About 4 seconds to load @28.8
This is the same image compressed with low quality (high loss) compression. The difference in quality is not significant for most web sites, but the size reduction is (2.7X).

Here is the detail:
Enlarged low quality JPG