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Re: filmscanners: Setting screen gamma problem



Jean-Pierre - Thanks, I took your advice and other suggestions, and my 
story is ...

I followed the Photoscienta page http://www.photoscientia.co.uk/Gamma.htm , 
and successfully set up my gamma - I selected a gamma of 2.0.  Checked it 
at two other sites with good test patterns (Timo's gamma = 2.0 test pattern 
(yes it is NOT true as I believed that everything on his pages was for 
gamma = 1.0!) at 
http://www.aim-dtp.net/aim/evaluation/gamma_space/index.htm and Hans 
Brettel's  gamma checking applet 
http://www-sig.enst.fr/~brettel/TESTS/Gamma/Gamma.html).

(The Photoscienta test pattern is the most sensitive and simplest to use to 
set the gamma, but read on...)

Both these checks showed that my setting was good at only one greyscale 
level, and that at the dark end and the bright end my "gamma" was way 
off.  This led me to investigate more the effect of black point setting; I 
soon realised that this is CRITICAL and that Photoscienta's test patterns 
are not sensitive enough to indicate whether your black point is correct or 
not.

In passing ... I believe that the Adobe Gamma Utility is very poor at 
setting black point - and was responsible for my original bad adjustment at 
the bottom end.  I have checked it again, and it gives me wrong setting for 
black point each time.

After adjusting black point using brightness control and comparing scanned 
parts of the screen to unscanned part, I reset gamma and it checks 
perfectly with both the above tools, over the whole range from dark to bright.

And the result is that my screen looks fairly similar to how I had it set 
up before all this trouble began(!), except that I can discern the lower 
levels of my step wedge when I couldn't before.

BUT - the step wedge is still somewhat compressed towards the black 
end.  To get it looking "even" steps over the range, I have to adjust gamma 
towards the ridiculous extreme, maybe around gamma = 1.3 or so.  Hence my 
original question -  should such a step wedge look evenly spaced on a well 
set up monitor?

I remain with this problem, and the fact that even with my new setup, my 
web photos look OK on my screen but light, pale and washed out on a number 
of other screens.  Maybe the latter is coincidence and I have looked at a 
bunch of badly set up monitors???  Anyway, I continue to research...

Julian


At 06:17 28/06/01, you wrote:
>Me too I struggled a lot with calibrating my Viewsonic PF815 22' monitor.
>I used Adobe Gamma on the Gamma-space 2.2 monitor calibration chart made by
>Timo Autiokari on www.aim-dtp.net. and
>http://www.aim-dtp.net/aim/evaluation/gamma_space/index.htm. He made also
>many other gamma charts.  I downloaded the 2.2 chart and placed it as the
>desktop wall. Withy Adobe Gamma I managed to get a quiet good calibrated
>monitor on all the grey values from deep black to high white. When looking
>at the Yellow Rose from Lawrence W.Smith in PS6.01 I can see clearly the
>subtle details in the leave and the beautifull colors in the rose. It
>indicates me that my calibrtion is correct.
>I suggest you try this too and see what it gives...
>
>Jean-Pierre Verbeke


Julian Robinson
in usually sunny, smog free Canberra, Australia




 




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