The WebXealot Page 3

Xara X. Bitmaps (Continued)

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JPEG Compression JPEG images are able to achieve remarkable amounts of file compression by using a method called Lossy Compression. Simply stated, this method looks at the information contained in the bitmaps, much of which is hidden, and throws out all but the visible information. This achieves a good looking image with a manageable file size.

Unfortunately, because much information has been deleted from the file, if you attempt to resize the JPEG and resave it, the image quality will degrade noticeably. The amount of compression also affects the appearance of the image.

Xara measures compression kind of backwards (in your editor's opinion). A file that shows 80% on the compression slider has been compressed 20%. See what I mean?

For comparison, the JPEG image shown here has 0% compression or 100% on the Xara scale. Notice how clean the text appears and how solid the colored band at the top of the image is. The file size is 51K.

Here is the tradeoff. This file has been compressed 25% (75% on the Xara scale). The color in the photograph looks just about the same. And the white text at the bottom is still pretty clean. But the solid colored rectangle at the top looks a little blotchy.

On the other hand, the file size has dropped dramatically from 51K to 13K.

Dropping the compression to 50% (50% on the Xara scale) reduces the quality of the white text on the bottom a little and the text and solid colored rectangle a lot. The photo still looks good. The file size has only dropped to 9K. We have passed the point of diminishing returns.

By way of comparrison, the file compression here is 75% (25% on the Xara scale). The photo looks mushy, the text looks mushy, the rectangle and text on top look mushy. But the whole image is only 6K!

With a little experimentation, you can usually reach a happy medium between image quality and file size.

Surprisingly, I saved this image as a 256 color GIF file, using the settings recommended by Xara, and the file size is only 32K. A lot larger than the JPEG at 80% compression, but not too bad for a GIF image.

We'll return to GIF settings a little later on.