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Author Topic: THE GREEN SCREEN FOR THE WEATHERMAN  (Read 4611 times)
K0YNE
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« on: April 21, 2009, 10:41:56 AM »

I WANTED TO POST AN INTERESTING TOPIC ABOUT THE GREEN SCREEN THAT IS PAINTED ON THE WALL
FOR THE WEATHERMAN.
WHILE AT UNK, WE HAD PURCHASED A NEW SWITCHER, A GRASS VALLEY 110 WITH CHROMA KEY
CAPABILITIES. WE PAINTED OUR WALL GREEN AND WITH GREAT RESULTS, WE COULD DO WHAT TV
STATIONS HAD BEEN DOING FOR MANY YEARS.

HERE IS HOW IT WORKS.
 A DEDICATED CAMERA IS USED FOR THE WEATHER. WHEN THE CAMERA IS TURNED ON AND IS LOOKING AT THE GREEN WALL, IT'S OUTPUT THRU THE RGB LINE, HAS AN INTENSE GREEN VOLTAGE OUTPUT.
SINCE ALL CAMERAS ARE ROUTED THRU THE SWITCHER, THE CHROMA KEY CAMERA IS SELECTED.
ITS VIDEO IS SEEN ON A MONITOR AS AN ALL GREEN SCREEN. THE SWITCHER NOW IS SELECTED TO
CHROMA KEY. TWO OR MORE CONTROLS MAY BE USED ON THE SWITCHER TO RESOLVE THE GREEN COLOR. NOW, THE HUE OR COLOR RANGE CONTROL IS ADJUSTED TOWARD THE GREEN COLOR RANGE.
AS THE CONTROL IS TURNED AND BEGINS TO APPROACH GREEN, A CHANGE ON THE MONITOR NOW
BEGINS TO MINIMIZE THE GREEN COLOR, A FINE TUNING OF THE SATURATION CONTROL WILL PEAK
THE EFFECTS OF THE REMAINING GREEN ON THE MONITOR AND THE FINISHED PRODUCT IS A GRAY SCREEN OR A SCREEN WITHOUT COLOR. WHAT HAS HAPPENED TO THE GREEN?
IN ELECTRONICS WHEN TWO VOLTAGES ARE THE SAME IN AMPLITUDE AND ARE 180 DEGREES OUT OF
PHASE, THE OUTPUT IS REDUCED TO ZERO. SO AS THE SWITCHER WAS ADJUSTED TOWARD GREEN,
AND EXACTLY 180 DEGREES OUT OF PHASE IS WHEN THE GREEN WAS ELIMINATED. NOW THIS SIGNAL
IS SENT ON DOWN STREAM AND A OVERLAY CAN BE ADDED SUCH AS A WEATHER MAP.
CHROMA KEYING IS USED EXTENSIVELY IN MOVIES FOR SPECIAL EFFECTS.
NOW YOU CAN TELL SOMEONE ELSE HOW CHROMA KEYING WORKS. PAUL K0YNE
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