[Openicc] new version of xcalib

[Jonas Gall]

On Fri, 04 Mar 2005 14:39:14 +1100, Graeme Gill <graeme at argyllcms.com> wrote:
> Stefan Döhla wrote:
> > Additionally, a Win32 version is available. It can be used as an
> > alternative to commercial gamma loaders. You may place it in Autostart
> > to load the vcgt-content to your video-card's LUT on start-up.
> 
> I was having a look around at various OS's, trying to see how each
> copes with setting up RAMDAC values, from the point of view
> of setting these curves, and being able to manipulate them to
> do calibration. If anyone has any comments, corrections, additions
> or further pointers to my summary, please add them.
> 
> Graeme Gill.
> 
> -------------------------------------------------------------------------------
> Monitor calibration interfaces on various OS's
> -------------------------------------------------------------------------------
> 
> MSWindows:
>         Windows NT4 doesn't seem to have support for loading RAMDAC
>         values. Get/SetDeviceGammaRamp() don't do anything under NT4.
>         There seems no standard way around this, even if the underlying
>         video drivers support it, since you can't open the video driver
>         directly from user or even kernel space to send it an ioctl.
>         Somehow the Nvidia GeForce4 tools are able to communicate
>         with the NVidia drivers, since it's user tools have a "Color correction"
>         pane that sets the Red, Green and Blue curves on my NT4 system. How it
>         does this is a bit of a mystery.
> 
>         Presumably on Windows 2000 and XP, Get/SetDeviceGammaRamp() works
>         as advertised.
> 
>         The Get/SetDeviceGammaRamp() functions cope with up to 16 bit
>         table entries (allowing for 10 or more bit RAMDACs).
> 
>         For Longhorn they are promising something more integrated with the
>         new Windows Color Architecture (perhaps much like OSX).
> 
> Mac OSX:
>         Has a whole interface for dealing with this stuff (Quartz services),
>         and automatically sets the RAMDACs from the selected screen profile.
>         Unfortunately the CGGet/SetDisplayTransferByTable() functions only seem
>         to handle 8 bit entries, meaning that RAMDAC capabilities can't be fully
>         utilized, unless it can be represented as a color "formula".
>         This seems like a problem for high quality color display.
> 
>         See :
> <http://developer.apple.com/documentation/GraphicsImaging/Reference/Quartz_Services_Ref/index.html>
> 
> X11:
>         In theory a Direct Color Visual lets you set the RAMDAC values by setting
>         the colormap values, and handle up to 16 bits per component. In practice
>         this interface seems rather oriented to individual applications, rather
>         that setting global screen parameters, so the XVidModeExtension seems
>         a more appropriate path, and XF86VidModeSetGammaRamp() apparently handles
>         up to 16 bits per color component.
Pseudocolor visuals can do 16bits per color component, too (most
popular consumer seems to be Xprint which does 12bit for Postscript
printers if I read https://bugs.freedesktop.org/show_bug.cgi?id=1299
right).

Jonas
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