[EXPERT TIPS][GUY KUO]
Setting Contrast
How many times have I read people complain that they simply don't know how high to set
their contrast?
AVIA shows you how to look for danger signs like blooming but the final instruction is
often forgotten or ignored. Turn down contrast (white level) to the LOWEST point that
still lets white appear white. Still, people think that their not recognizing blooming
means they can keep their displays cranked up. Even worse some mistakenly think this means
you should keep the display just under the point of blooming. NO. NO. NO!
The goal is to set the display as DIM as possible but still bright enough to be
enjoyable in controlled light conditions. That is a white level (contrast) such that white
on screen has an apparent luminance of 13 to 20 foot lamberts. I didn't state the
target in AVIA in terms of Foot Lamberts because nobody other than calibrators has a video
appropriate light meter in their kitchen drawer.
Lacking such a device, the best and safest is to admonish people to turn contrast down
too low and then back contrast up to the point that white just begins to look white again.
That's usually just above 12 FL. We get asked why the pattern doesn't have something
that appears or disappears like we can for setting black level. You can't build in an end
point like that for white level because there isn't a physical limit like the absence of
light which defines black.
White can be a huge range of luminance up to infinity. Black, well is black so you can
have a hard end point built into the pattern. Once you hit black it's black. Lacking a
light meter, the other way to solve this is to have people compare their white against a
known brightness lamp. Your flashlight and my flashlight aren't going to be the same. Even
if we get the same light bulb, they are going to vary with their age. So we've been stuck
- until now.
A Way Out -- And into the Fire
A butane lighter which has the same flame height should produce roughly the same amount
of light and be usable as a very rough measure of light level. Granted it is not the same
color as the white on screen but you can visually compare relative brightness of lights
despite color differences. Just don't set anything on fire while trying this at home. This
is just for adults who know how to use a lighter and realize that paper burns. Keep a fire
extinguisher handy and proceed at your own risk. You have been warned.
- Turn off all lights in the room and display the Needle Pulses & Log Scale patttern
in AVIA.
- Take a piece of white printer paper, in my case a piece of 20 lb Xerox "Primary
Image" white paper and hold it up in front of you so you can compare the brightness
of the paper versus the brightness of white in the pattern.
- Light your butane lighter (mine was a BIC).
- Move the lighter back and forth in front of the paper. I mean in front of the paper as
in closer to you than the paper.
At a distance of 2.5 inches from the paper, a one inch flame illuminates the paper
about as brightly as 13 Foot Lamberts on the screen. A 3/4 inch flame does the same at
about 2 inches. Adjust your white level (contrast) to make white that amount of
light.
This should work as a rough estimate of how luminous white actually should be. It's
certainly not a laboratory grade measurement but at least you get some idea of the light
level we're aiming at for white.
Most people will be shocked at how low that actually is. This is a level for fully
controlled (dim) lighting conditions. You can go up to a higher level for more ambient
light, but be aware that you are wearing your CRT's more rapidly and making them prone to
burn-in if you use white levels higher than 13 to 15 FL. Once more, be careful with
the lighter or you will experience an unwanted, new definition for what "torch
mode" means in home theater.
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