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Re: How to set >8 bit RAMDAC values on a display ?

Subject: Re: How to set >8 bit RAMDAC values on a display ?
From: Mike Paquette <email@hidden>
Date: Wed, 11 May 2005 23:30:20 -0700
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The use of CGSetDisplayTransferByTable() is preferred to CGSetDisplayTransferByByteTable(), which is present primarily for legacy environment support.

CGSetDisplayTransferByTable() sets the gamma from arrays of CGGammaValue, a floating point representation supporting a mantissa of 23 bits, for each color channel. This should provide adequate precision for RAMDACs planned for the near future.

The CGGammaValue entries should lie in a range from 0.0 to 1.0, where 0.0 represents minimum drive signal level, and 1.0 represents maximum drive signal level.

CGDisplayErr CGSetDisplayTransferByTable (
   CGDirectDisplayID display,
   CGTableCount tableSize,
   const CGGammaValue * redTable,
   const CGGammaValue * greenTable,
   const CGGammaValue * blueTable
);


On May 11, 2005, at 10:59 PM, Graeme Gill wrote:

Looking through the Quartz Services Reference, I found:

<http://developer.apple.com/documentation/GraphicsImaging/Reference/ Quartz_Services_Ref/index.html>

CGSetDisplayTransferByByteTable

Sets the values in the 8-bit RGB gamma tables for a display.

CGDisplayErr CGSetDisplayTransferByByteTable (
   CGDirectDisplayID display,
   CGTableCount tableSize,
   const CGByteValue * redTable,
   const CGByteValue * greenTable,
   const CGByteValue * blueTable
);

but nothing that supports better than 8 bit RAMDAC values.
Most graphics cards have had 12-14 bit RAMDACs for the last
10 years or so. Is there any API for setting the higher
precision values necessary for high quality greyscale
calibration of a display ?

(By comparison, both Windows 2k and X11 support 16 bit RAMDAC entries).


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	>How to set >8 bit RAMDAC values on a display ? (From: Graeme Gill <email@hidden>)

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