What's the difference
between a GIF and a JPEG?
 

Consider the Number of Colors in the Image

GIF and JPEG are the two most common image formats on the WWW.  JPEGs are capable of displaying images that have millions of colors in their palette, while GIFs can only display 256 colors in an image.  Therefore, JPEGs are particularly good for displaying photographs and real world images, or perhaps even some computer-generated images with complex color schemes.   In the table below, compare the JPEG on the left and the GIF on the right.  If your monitor is configured to display millions of colors, you should see a significant difference.  But if your monitor is configured to display only 256 colors, there would be a negligible difference in quality (if any at all) between the two images.

Photos and Images with Complex Color Schemes

The left graphic is
a jpeg/jpg image. 
It displays a spectrum
of 16.7 million colors. 
This particular image
 has a file size of 6KB.

The graphic
on the right
is a gif image.
It can display
a maximum spectrum
of only 256 colors. 
This particular image
has a file size of 5KB.

Winner:  JPEG

JPEG is very good at compressing a broad color spectrum. 

GIF is limited to only 256 colors.

Use Internet Explorer 5.x or above and
click here to compare GIFs and JPEGs
for displaying photos.
 

Graphics with Relatively Simple Color Schemes

Both these graphics have file sizes of about 1.5KB. But for this JPEG to match the small file size of the GIF, it must be compressed so much that there is a great deal of distortion. Even with such high compression, this JPEG still uses a whopping 2709 colors in its palette.  A JPEG is capable of clearly displaying this image, but compression would have to be much lower, resulting in a larger file size.

 The quality of this GIF would be the same whether its palette had 256 colors (GIF maximum), or just 5 colors. But the palette has been deliberately reduced to only 5 colors to greatly reduce the file size. The only way JPEG can compete with such a small file size is to greatly compress the image, resulting in distortion.

Winner:  GIF

As the number of colors in an image's palette approaches or surpasses a GIF's maximum of 256, JPEG, with its powerful compression capabilities, becomes a wiser choice. But with a simple color scheme, GIF provides a small file size without necessarily sacrificing image clarity.

Use Internet Explorer 5.x or above and
click here to compare GIFs and JPEGs
for displaying graphics with simple color schemes.

 

Features

While JPEGs are static images, GIFs can be animated.  Also, you can designate one color in a GIF as transparent, so that whatever is behind that color shows through the image.

Animation

This JPEG is set to a compression factor of 15, resulting in a clear image with a file size of 6.9KB.

Because this GIF has several layers to produce animation, the file size is higher (16.6 KB) than if it were a static image. 

 

Transparency

To make this JPEG appear transparent, we have to change the background color of the image to exactly match the background color of this table.  Even so, it isn't true transparency.

The background color of this GIF is actually white, but white has been selected as the transparent color for this image.  Off-white colors still appear because transparency applies only to one exact color within a single image.

When the background of the table is changed, the JPEG no longer simulates transparency.  Once again, we'd have to change the background color of the image to match the color of the table.

 Once the transparent color of a GIF is set, that color will always be transparent, regardless of the table's background color.  That is, this GIF, and the one above it, are exactly the same image.