[opendtv] Re: RGB mania
- From: "Peter Fasciano" <Peter_Fasciano@xxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>, "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- Date: Tue, 18 Jan 2005 13:37:51 -0500
A very short history of Gamma in video.
In 1936 the BBC was the first organization to deploy a clear gamma =
strategy in broadcasting. They first applied a gamma amplifier located =
after the video switcher. All camera outputs and all monitoring scopes =
worked with the raw video signal from the emitron tube cameras (similar =
to iconoscope design) which had a 1:1 output signal correlation to the =
light input. =20
Within the first year of operation the BBC radically modified their =
gamma deployment strategy. They removed the special gamma amplifier =
from the switcher (vision mixer) output and relocated the gamma circuit =
to the video amplifiers in their emitron cameras. =20
What they knew at the start:
The gamma circuit corrected the camera output to correspond to the =
response characteristic of the CRT control grid design.
When the video signal is converted from its raw form to the gamma =
modified form (approx .45) the atmospheric noise of the OTA transmission =
becomes evenly distributed across the luminance range. =20
What they gained by moving the gamma function to the camera.
The monitoring scopes provided a representation of the camera output =
signal that was much easier to interpret. =20
Camera shading/matching became easier to accommodate with the improved =
signal monitoring.
The vision mixer function was improved as the signals could now be =
"linearly" blended with faders. =20
Much of this development work is attributed to Alan Blumlein who was the =
tech lead at the London Station.
Pete Fasciano =20
Fellow, Advance Development =20
Co-founder, Avid Technology =20
1925 Andover St. B2-3 =20
Tewksbury, MA 01876 =20
Ext: 978-640-3308
Fax: 978-640-3116
peter_fasciano@xxxxxxxx
-----Original Message-----
From: Henry Baker [mailto:hbaker1@xxxxxxxxxxxx]
Sent: Tuesday, January 18, 2005 12:47 PM
To: Allen Le Roy Limberg
Cc: opendtv@xxxxxxxxxxxxx
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