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The Day the Green Died
Written January 6, 2015


This blob represents all the colors that the human eye can see.  Television sets emit green, red, and blue light represented by the points of the black triangle, combining them in an attempt to depict all these colors.  But television can’t actually depict the colors outside the triangle.  That’s why Santa’s suit on TV is red, but never brilliant red.

This particular triangle corresponds to the official “color gamut” known as 709.  Engineers are in the process of improving TV to achieve wider, more realistic gamuts.  But in the meantime, our eyes have to pretend we’re seeing all the colors.

In the late 20th century, the main TV in my apartment was a 25-inch NEC.  It worked fine — until the green went away.  The cause was probably a burnout of one of the three electron guns in the picture tube.  The set could no longer display all the colors in the triangle, but only those on the R-B edge.

I promptly bought a new Sony to serve as my main TV and exiled the NEC to my bedroom.  A few years later, its blue gun also failed and I banished it to the trash heap.  But until then, I occasionally found myself in the bedroom watching it.

As I’ve simulated here, the pictures were in color, just not quite the right color.  Note the missing green bar on the test pattern. 

After a few minutes of staring at this magenta screen, my mind adapted to what appeared to be unusual lighting conditions and filled in the missing data to make the scenes look almost normal.

This is obviously a scene from a football game.  I know the field is green, so the grass looks green to me.  I know Michigan wears uniforms of maize (golden corn) and blue, so the pursuing linebacker's pants look gold to me.

But if we zoom in and isolate those details from the other cues in the picture, we discover the pants are actually red and the grass is almost black.

When I got tired of the saga of Bill and Monica after half an hour, I glanced away from the TV screen.  The real world had a greenish tint until my eyes readjusted.

The moral:  Our vision forgives color irregularities by adapting to what it sees.

My present high-def LG television has overall picture modes called Standard, Eco, Cinema, Game, Expert1, Expert2, and Vivid.  I can also select from color gamuts labeled Standard, EBU, SMPTE, BT709, and Wide.  I can tell the difference, but I could watch almost any of these modes.

Then I can make further adjustments for backlight, contrast, brightness, horizontal sharpness, vertical sharpness, color, tint, red, green, and blue.  In the color management system I can adjust the saturation, tint, and luminance of red, green, blue, cyan, magenta, and yellow.  I can even look at only red, only green, or only blue.  And I have other choices.  I don’t even know what some of these are.

Dynamic contrast: off, low, high
Gamma: 1.9, 2.2, 2.4
Color temperature: cool, medium, warm1, warm2
(Color temperature can also be adjusted over a 100-step range)
Method: 2 points, 20 point IRE
Pattern: outer, inner
Points: high, low
Real cinema: on, off
Edge enhancer: on, off
Noise reduction: off, low, medium, high
MPEG noise reduction: off, low, medium, high, auto
Black level: low, high, auto

When a live TV program originates, for each camera the video operator has controls to adjust parameters like these and more.  His task is to precisely match all the cameras, so that when the director cuts from Camera 1 to Camera 2 the picture does not suddenly become slightly redder.

But when I’m watching a TV program at home, I don’t have to match my picture to any other picture.  Should the brightness be set to 70 or to 71?  I don’t care.  I don’t bother with fine adjustments.  Almost any setting looks okay to me, as long as there’s at least some green in it.     



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