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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.
Juan Rivera
Comments (6)
Dec 01
Brian Madden says:
You know, this is not at all how I thought it worked. I just assumed that it wou...You know, this is not at all how I thought it worked. I just assumed that it would send the 32-bits down to the client, so if you had a seamless window (for example), it could alpha blend the remote app with the local desktop. But it sounds like all 32-bit apps are pre-blended on the remote host, so the local client only sees is as a 24-bit app, right?
Dec 02
Anonymous says:
"Most DirectX applications require a GPU" That may be true but what about the Wi..."Most DirectX applications require a GPU"
That may be true but what about the Windows games in Windows7? They don't require a GPU but they don't run on XenDesktop.
I suspect there are also other Windows (inbox) applications that use DirectX that don't require a GPU but they wont run either. And then you get to apps written by in house developers and ISVs. Again they may have chossen to use directX but not need a GPU.
Would it not be better to tell the OS you support 32bit and give the apps a chance to run, and let us decide if we want to use them in a VDI environment.
Dec 02
Juan Rivera says:
WPF applications are also DirectX-based applications and can use a CPU-base...WPF applications are also DirectX-based applications and can use a CPU-based software renderer as well.
In Vista/Win7, WPF applications run fine inside a 24-bit color session.
Juan
Dec 16
Anonymous says:
That is good news that WPF applications that want 32bit graphics run. But that ...That is good news that WPF applications that want 32bit graphics run.
But that still leaves at least the Windows7 games not running because of lack of 32bit support. And I know we are spitting hairs but I bet its easier for Citrix to code ICA so that any API that asks gets told that 32bit graphics is supported than for us to request changes from the to the first app we find that fails to run becuase of lack of 32bit support.
And I'll give you another reason why I expect to see 32bit support in the next release of XenDesktop:
Dec 16
Juan Rivera says:
XenApp for Windows 2008 R2 beta supports 32-bit color sessions. Check it out...XenApp for Windows 2008 R2 beta supports 32-bit color sessions. Check it out...
Dec 14
Anonymous says:
What's the big deal, as RDP7 supports 32 bit color against the OS you are demons...What's the big deal, as RDP7 supports 32 bit color against the OS you are demonstrating? I don't need ICA for that?
This is interesting information though.
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