A number of people have asked me whether XenDesktop can deliver applications in 32-bit color. Typically, this question reflects confusion around the difference between color depth and transparency. The false assumption is that 32-bit color must be better than 24-bit color. So what is 32-bit color and how does XenDesktop handle it?
What surprises many people is that 32-bit color and 24-bit color actually deliver the exact same range of colors. Both settings deliver what is known as “True Color”, a palette of 16,777,216 different colors. 24-bit color contains three channels: Red, Green and Blue. Each channel has 8 bits. 32-bit color adds an extra 8 bits (one byte) called the alpha channel. The alpha channel is used to create the effect of transparency. It does not increase the color depth; you still get 16 million colors, which is plenty for high quality photographic images and complex graphics. So, “32-bit color” is actually a misnomer as regards color depth since not all of those bits are used to represent color.
The following illustration shows how a bitmap with alpha information blends with its background:
In this illustration the windows have different values of transparency. The one on the right is completely opaque.
XenDesktop 4 supports the alpha channel
XenDesktop 4 supports 24-bit True Color sessions and it also fully supports the alpha channel. What happens is that all 32-bit images are collapsed onto the screen into a 24-bit image. The resultant 24-bit image is then sent to the client.
The following video shows XenDesktop support for applications using 32-bit images:
When do you really need a 32-bit color session?
The main reason you may need a 32-bit color session is if your application explicitly requests it. This can be the case with DirectX-based applications that run in 16-bit or 32-bit color, but not in 24-bit color. Most DirectX applications require a GPU in which case you will need HDX 3D for Professional Graphics. HDX 3D Pro Graphics fully supports 32-bit color sessions. And XenApp for Windows Server 2008 R2 (available for Tech Preview later this month) will provide another solution for delivering applications that support True Color but cannot run in 24-bit color mode.