The SpeedScreen folder contains a rule that enables you to remove or alter compression. When client connections are limited in bandwidth, downloading images without compression can be slow.
Image Acceleration Using Lossy Compression
This rule defines ways in which images can be compressed to improve the responsiveness of graphics-intensive applications:
- Normal lossy compression
- Progressive display compression
- Heavyweight compression
If your server farm includes servers running different releases of XenApp, you may not be able to apply all of these image acceleration techniques to all of the servers in the farm. Citrix recommends that you maintain all servers in a farm at the same release level.
If this rule is not configured, SpeedScreen Image Acceleration applies image compression as follows:
- Normal lossy compression is applied with Medium compression/medium quality for all connections. This provides better session performance at the cost of a slight reduction in image quality.
- SpeedScreen Progressive Display is enabled with a threshold of 1 megabit per second.
- Heavyweight compression is disabled.
Optimizing Image Acceleration
Citrix recommends optimizing these image acceleration settings to suit your deployment. Factors such as the type and quality of images, network configuration, and which graphics applications you use affect the user experience. Determine the optimum settings by adjusting the Compression level, its Threshold value, and by selecting Heavyweight compression. For example, enabling lossy compression but with no threshold can improve the display speed of high-detail bitmaps (such as photographs) over a LAN.
This setting controls the normal lossy compression level used over client connections that are limited in bandwidth. In such cases, displaying images without compression can be slow. The Compression level setting defines the degree of lossy compression used on images. For improved responsiveness with bandwidth-intensive images, use high compression. Where preserving image data is vital; for example, when displaying X-ray images where no loss of quality is acceptable, you may not want to use lossy compression.
Enter the maximum bandwidth in kilobits per second in Restrict compression to connections under this bandwidth. The Compression level setting is then applied only to client connections under this bandwidth.
SpeedScreen Progressive Display Compression Level
Slow initial download of images can be frustrating for users. The SpeedScreen Progressive Display compression level setting provides a less detailed but faster initial display. The more detailed image, defined by the normal lossy compression setting, appears when it becomes available. Use very high or ultra high compression for improved viewing of bandwidth-intensive graphics such as photographs.
Enter the maximum bandwidth in kilobits per second in Restrict compression to connections under this bandwidth. The SpeedScreen Progressive Display compression level is then applied only to client connections under this bandwidth.
For this feature to be effective, the SpeedScreen Progressive Display compression level setting must be higher than the Compression level setting. By default, it is two settings higher. For example, if Compression level is set to medium compression, SpeedScreen Progressive Display compression level is set to very high compression.
Note: The increased level of compression associated with SpeedScreen Progressive Display also enhances the interactivity of dynamic images over client connections. The quality of a dynamic image, such as a rotating three-dimensional model, is temporarily decreased until the image stops moving, at which time the normal lossy compression setting is applied.
Use Heavyweight Compression
Heavyweight compression allows you to reduce bandwidth further without losing image quality by using a more advanced, but more CPU-intensive, graphical algorithm.
If enabled, heavyweight compression applies to all lossy compression settings. It is supported on the Citrix XenApp Plugin for Hosted Apps but has no effect on other plugins.
Use this rule to set the maximum amount of bandwidth available to this feature in client sessions.
TWAIN devices are image acquisition devices, such as scanners and digital cameras, that use manufacturer-supplied, industry standard TWAIN drivers. TWAIN redirection (enabled by default) allows users to access client-side TWAIN devices from published image processing applications.
After enabling the rule, enter the maximum amount of bandwidth in the Limit box. The value you enter is either in kilobits per second or as a percentage of overall available bandwidth, depending on whether you choose the Session Limits folder or the Session Limits % folder.
To set a compression level for image transfers or to disable TWAIN redirection, use the rule Client Devices > Resources > Other > Configure TWAIN redirection.