I am setting up a terminal server farm where the desktop shows our corporate branded background image. The problem is that the RDP session is limited to 16-bit color, and it creates a visible and annoying vignette pattern in the image which looks unprofessional.

Is there any way to downsample the image to a 16-bit color palette and use dithering to reduce the color banding in the image?

I'd rather use GIMP since it's free but I can borrow a computer with Photoshop in it if I have to.

closed as off-topic by Zoredache, Massimo, kasperd, MDMoore313, mdpc Jun 23 '14 at 22:07

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  • Not sure whether to upvote because it's a Remote Desktop Services question, or downvote because it's a Photoshop question... – Ryan Ries Jun 20 '14 at 18:48
  • I cross-posted it on the Graphics Design forum as well, but I am a sysadmin, not a graphics designer, and there are more eyeballs on this forum. – Wes Sayeed Jun 20 '14 at 18:49
  • Please do not crosspost. Please do not post here, simply because you feel there is more eyeballs. The actual question should be on-topic here. – Zoredache Jun 20 '14 at 19:08
  • I feel it is on-topic. Branding a terminal server is a legitimate system administration function, and @Evan's answer is exactly the kind of information I had hoped to glean from this forum. Sysadmins understand how RDP works. Graphics designers know how Photoshop works. But it is rare to find someone who is adept at both, so a cross-post is appropriate in this case. – Wes Sayeed Jun 20 '14 at 19:22

The RDP GDI Acceleration Extensions document is the closest thing I can find to an official reference, and it makes references to 16-bit RGB values being sent across the wire for things like GDI brushes as being 5/6/5 format (5 bits of red, 6 bits of green, 5 bits of blue). 5/6/5 has always been how Windows has handled 16-bit video modes (at least, in my memory) so I'd be inclined to grab a Photoshop filter that dithers to 5/6/5 format and tweak from there.

  • I found the solution on an Adobe community forum. I'm giving you credit because the 5/6/5 format was the magic Google sauce that allowed me to find the answer. I added some noise and then dropped the palette to 256-colors. It now looks indistinguishable from the original. – Wes Sayeed Jun 20 '14 at 22:35

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