Hi,

D3D10 requires 10.0 hardwares to support scan out for R10G10B10A2_UNORM
D3D9 let hardware support A2R10G10B10 as display format

a) aren't theses D3D9/D3D10 formats are swizzled ?
  (then D3D9 support 'll be unusual)
  NVidia doesn't seem to support this D3D9 format as a display one, don't know for Amd

b) I assume gamma space is Linear, but I think
   DXGI_FORMAT_R8G8B8A8_UNORM_SRGB is better than
   DXGI_FORMAT_R10G10B10A2_UNORM
   because of visible bandings in dark colors
   then what is the purpose of this scan out property ??

Thanks
JSeb

a) I'm not sure I understand your question.  The bit layout of the pixels is as described in the format enum.  If the device native storage layout is different, then the driver handles that when communicating raw data to/from the card.  In other words, you shouldn't care if its bit layout is different in the hardware.

b) Display formats in sRGB space have already had a standard gamma applied to them.  While this is "standard", its not going to be the best match for every monitor.  The best approach to gamma is to handle it properly yourself by measuring the gamma of your monitor interactively and then applying an appropriate gamma ramp for that monitor.