My monitor reports a gamma of 2.85 when asked (it's PNP and there are
programs that can do such queries). However, the various calibraiton
utilities show it sa being 2.2 - 2.3. Who do I trust and why the
difference?


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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Peter Popov wrote:
> 
> My monitor reports a gamma of 2.85 when asked (it's PNP and there are
> programs that can do such queries). However, the various calibraiton
> utilities show it sa being 2.2 - 2.3. Who do I trust and why the
> difference?

The icc profile that came with my Sony was gamma 2.6 and I measured it
as 2.5 with the gamma.gif. There are various things to consider when
estimating gamma visually.

Ambient light level changes gamma. Lower ambient light level and
minimize glare.

Brightness changes gamma. Adjust the black level so that lowering
brightness doesn't produce visible change in black background.

Contrast changes gamma. Adjust amplification so that increasing
contrast doesn't produce any brighter white.

The test pattern used for estimation changes gamma. The chessboard
pattern is worst. Vertical lines are better. Horizontal lines are best.


Monitor's age changes gamma. Monitors from the same production line have
different gamma though I don't think they could differ more than 10%.
This is because it's difficult to build high voltage circuits to strict
tolerances.


These are the issues that I know of and using these I have managed to
to produce fairly consistent results with different monitors.

Remember it's only a crude estimate. Only photometric measurements will
tell the truth but I leave that to the professionals :)

______________________________________________________________________
Kari Kivisalo                                  http://www.kivisalo.net

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Kari Kivisalo wrote:

>Only photometric measurements will
>tell the truth but I leave that to the professionals :)

How about rendering a series of images (with gamma 1), only containig one 
gray value, going from 0 to 1. Display these on the screen. Push the lens 
of a camera, with true the lens light measurement, against the screen and 
measure the brightness of each image. Calculate gamma.

Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

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