I've tried following the instructions of how to use "gamma.gif" to determine
the display gamma but I find that the gray on the left always looks
significantly brighter than any of the numbered patches... does this mean
that my moniter is much brighter than most or is it likely that I am doing
something wrong? Are there any other ways of determining display gamma?

Thanks.

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John Vodden wrote:

> I've tried following the instructions of how to use "gamma.gif" to determine
> the display gamma but I find that the gray on the left always looks
> significantly brighter than any of the numbered patches... does this mean
> that my moniter is much brighter than most or is it likely that I am doing
> something wrong? Are there any other ways of determining display gamma?



A natural gamma of more than 3 ?
Me think your system might already try to correct some gamma...and does 
it in the wrong direction.

Or you have turn the brightness too far ?

What is your system (hardware & OS please) ?

Check if your displaying program has not an option to automatically 
gamma correct a picture (you should desactivate it).

How I compute my gamma on W98, on a Voodoo3 2000 PCI:
=====================================================

I set the brightness of the monitor to "Centered",
Contrast was 100%, and the gamma control center was set to a gamma of 1.0!
I opened gamma.gif with xnview (and in the options tab, the gamma
correction was not active)
instead of going 5 meters away, I closed my eyes and reopened just 
enoough to get a blurry feeling, comparing the left part with the right 
part, I found a change in the feel of the grey between 2.6 and 2.8, so I
popped up the gamma control of the card, tuned the gamma knob to 2.7 and 
look again at the picture: the change of grey was now for the 1.0 entry.
So, I know that my system gamma is 2.7 when there is no gamma correction.

What I'm not sure yet, is wether I should kept a correction of 2.7 or 
one of 1.0 or just another one which would give a system gamma between 
1.0 and 2.7

Given that most viewer (including browser) do not gamma correct PNG 
files, and that I want to see the portfolio t_Grnt15 & t_Grnt17 images
(which are very black with a gamma of 2.7), I believe I will keep the 
correction of 2.7 so that my system just behave like a 1.0 display.
It might means more details in the shadows.

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in news:3D5### [at] freefr Le Forgeron wrote:

> What is your system (hardware & OS please) ?

Especialy if you use an lcd monitor you may be in trouble as they don't 
follow the smooth gamma curve of a crt monitor.

> Given that most viewer (including browser) do not gamma correct PNG 
> files, and that I want to see the portfolio t_Grnt15 & t_Grnt17
> images (which are very black with a gamma of 2.7),

If you have set the display_gamma in the povray.ini file to 2.7 when 
rendering the portfolio, you'd see the same as we do (when our systems are 
set up correctly).

Ingo

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"Le Forgeron" <jgr### [at] freefr> wrote in message
news:3D5### [at] freefr...

> What is your system (hardware & OS please) ?

Voodoo3 2000 PCI running win 98 (snap comes to mind!) I looked in the 3dfox
tools and the brightness contrast and colour sliders were all at 1.

> Check if your displaying program has not an option to automatically
> gamma correct a picture (you should desactivate it).

I was using MS paint, I'd be surprised if that had anything like that built
in!

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