Image Pyramids

The XMS packages include an option to generate multiple resolution versions of an image when it is imported. This can improve the display quality of an image when the native resolution is much higher than the screen resolution. In essence, if the image resolution is larger than the screen resolution, a the display of the image skips pixels so the image appears discontinuous.

The process of generating multiple versions of the image is referred to as Image Pyramids. If the feature is invoked, XMS will average 2x2 blocks of pixels in the image creating an approximate version of the image at half the resolution. This process is repeated on the smaller image creating an image at one fourth the original resolution, and so on. Up to four images are generated, based on the relative native resolution and the screen resolution. The goal is to get an image in the pyramid that is approximately the same as screen resolution.

When displaying all or part of an image, XMS determines which of the pyramid images have a resolution that most closely matches the current screen pixel size and uses that version of the image.

There are a few points to keep in mind when building pyramids. The initial generation of pyramid files can take several minutes, depending on the size of the original image and the computer hardware. Building pyramids uses more memory RAM. Building pyramids may not improve the on screen display of all images.

Once an image pyramid has been built for a particular image file, the user will not be asked again to build pyramids for that image file unless the image is moved or altered.

When pyramids are built for an image, up to four JPEG images are saved to disk. These image files can be saved to a temporary folder or can be saved in the same directory as the original image so that they are not regenerated each time the image is loaded.

Image Preferences

For XMS versions released after summer 2015, the default option is to not generate image pyramids and not even ask the user whether pyramids should be generated. This was implemented because the user of large static images has been largely replaced by dynamic images from web services, for which image pyramids do not improve quality, and greatly increase user confusion.

If a user has a large static image, and desires to generate pyramids, the user’s preferences for building pyramids can be set in the Images tab of the Preferences dialog (Edit | Preferences).

Related Topics

• Import from Web
• Registering an Image