Take a quick look at a typical page and a typical image and see what happens to their files sizes when they get compressed and sent up to the device.

A page's original size

Suppose a typical page has 15KB of HTML. This is actually a fairly large page, taking up several screens worth. You might accidentally have a few things included that are not supported on the device we are viewing with. (For instance, somebody with a Palm OS device can safely ignore all of the <font face="verdana" size="2"> tags.) This is the page file's original size.

A page's compressed size

The AvantGo sync server will take this page, strip out anything it does not need, and then compress the remaining text. Depending on the page, how well it compresses, and how much we strip out, the final size will probably end up somewhere between 3KB and 8KB. Assume it is 5KB for our example. This is the file's compressed size. This is the page size that is totaled up, along with any images, until the Maximum Channel Size is reached. A page's compressed size will vary with the type of device onto which it is downloaded.

A page's display size

This compressed page file is sent to the device, where it waits for somebody to view it. When a user asks to see the page on the screen, the AvantGo Client then uncompresses it. This will be approximately equal to its original size, minus any unsupported HTML we stripped out along the way. This is the file's display size. With our example page, this will probably end up being about 14KB. (Unless it is 2KB of HTML, and 13KB of unsupported client-side imagemap code.)

Image sizes

A similar process happens with images. With images, however, there are two important differences.

The first difference is that the compressed size (and the display size) will vary much more between different devices, because we will convert the image to the appropriate bit depth. For example, look at a 150x150 color JPEG that is 16KB. If I sync it to a 216-color Palm III, it will end up about 15KB. If I sync it to a 16-gray Palm V, it will end up about 12KB. And if I sync it to a 4-gray Palm III, it will end up about 6KB.

Image size limit

The second difference is that there is an absolute maximum size for images. Remember that at the moment, no matter how large your picture is originally, it will never end up larger than 150x150 pixels. Which means that the maximum theoretical size for any image is about 22KB (and in practice, it is smaller).

Note: If you need to, you can get around this image size limit by breaking the image in pieces and formatting it using a table. See Breaking the 150-pixel limit.