Vista Wallpaper Interpolation Solution

Although this may not be the point of positioning it, it is indeed a flaw and exists in the Vista RC2. When using a picture as a desktop wallpaper, Windows Vista is responsible for maintaining the aspect ratio of the image, but when compared to Windows XP, when the image is stretched to fit the screen resolution, Vista does not interpolate the image so that it appears jagged. In the following two graphs, the left is an example of the problem that shows a clear lack of interpolation (that is, commonly called jagged edges), and it appears to be smoother.

Vista Wallpaper interpolation problem

Sawtooth is caused by missing image interpolation. The so-called image interpolation is a process of image data regeneration--it regenerates a high-resolution image data from the original image.

In Vista, JPEG interpolation through the desktop Control Panel has not been properly performed. One of the most immediate results is that when you stretch a picture with a different screen resolution as a wallpaper, you will have a visual effect that you don't want to appear. This deficiency appears to appear only on JPEG images, while BMP images can accept the correct interpolation from the control Panel.

The "Set as desktop background" feature resolves this problem. The Set as desktop background feature leverages the PIX engine used by Windows Photo Gallery programs. PIX supports image interpolation, and when you set a picture as a wallpaper, you can apply it to the picture as well. As for why Windows Photo Gallery programs do not use image interpolation when zooming in on images, this may be categorized as a Microsoft alternative design.