Auto Color via Vertical Interval Reference signal (was Re: [Tig] Image from Peter Swinson)
ted at tedlangdell.com
Sat Jan 13 21:46:06 GMT 2007
Ted Langdell Creative Broadcast Services
Main: (530) 741-1212
Now with 3GHz MacPro powering Final Cut Studio
On Jan 13, 2007, at 8:29 AM, Rob Lingelbach wrote:
> On Jan 13, 2007, at 2:12 , Bob Friesenhahn wrote:
>> The TVs are not calibrated in the first place, and once the
>> customers get their hands on the TV remote, the colors are
>> adjusted to many whacky color schemes so that the pictures on the
>> TV sets don't look even close to similar.
> has there ever been any research done on a system that would
> provide automatic adjustment of TV receiver color/brightness/
> contrast based on a
> duplex data channel between broadcaster and the receiver? The home TV
> would have a built-in probe or sensor for ambient light and tube/
> LCD condition,
> and after the broadcaster received this data the TV would be
> automatically adjusted (quickly) to match a reference. This
> automatic feature could perhaps be engaged and disengaged..
> Rob Lingelbach
Back in NTSC's middle ages... the 1970's, a Vertical Interval
Reference (VIR) signal was inserted and used by sets equipped to use
it as a basis for automatic color adjustment. I'm not sure how many
stations still include it in their analog transmissions, and the FCC
changed its rules effective June 30, 1994 to allow only the Ghost
Cancelling signal mentioned below in the line that both the GC and
VIR had previously occupied.
The VITS (Vertical Interval Test Signal) still seen in analog
broadcasts allow bars, multiburst and other quality control signals
to be included in program video. Line selector scopes and waveform
monitors can be used to display just the video from that line, and to
determine whether the video being transmitted is legal, among other
things, and whether the transmission system's frequency response is
up to snuff.
The PAL system also has a VITS standard with insertion on specified
I recall some television sets having an ambient light photocell on
the front that varied the light output from the CRT as room
Great fun to modulate the CRT by tapping your finger over the sensor
hole. A CRT pulsing Morse code or to music was briefly
entertaining... and could annoy others if that was your intent.
Here are some links to VIRS details... perhaps more than you want to
Vertical interval reference. Reference signal inserted into the
vertical interval of source video. This signal is used further down
the video chain to verify parameters and to automatically adjust
gains and phase.
A more detailed description is on Wikipedia:
Vertical Interval Reference
The standard NTSC video image contains some lines (lines 1-21 of each
field) which are not visible; all are beyond the edge of the viewable
image, but only lines 1-9 are used for the vertical-sync and
equalizing pulses. The remaining lines were deliberately blanked in
the original NTSC specification to provide time for the electron beam
in CRT-based screens to return to the top of the display.
VIR (or Vertical interval reference), widely adopted in the 1980s,
attempts to correct some of the color problems with NTSC video by
adding studio-inserted reference data for luminance and chrominance
levels on line 19.  Suitably-equipped television sets could then
employ this data in order to adjust the display to a closer match of
the original studio image. The actual VIR signal contains three
sections, the first having 70 percent luminance and the same
chrominance as the color burst signal, and the other two having 50
percent and 7.5 percent luminance respectively. 
A less-used successor to VIR, GCR, also added ghost (multipath
interference) removal capabilities.
The remaining vertical blanking interval lines are typically used for
datacasting or ancillary data such as video editing timestamps
(vertical interval timecodes or SMPTE timecodes on lines 12-14 
), test data on lines 17-18, a network source code on line 20 and
closed captioning, XDS and V-chip data on line 21. Early teletext
applications also used vertical blanking interval lines 14-18 and 20,
but teletext over NTSC was never widely adopted by viewers .
FCC transmission standards related to the vertical interval: (partial)
(iv) Regardless of other provisions of this paragraph, after June
30, 1994, Line 19, in each field, may be used only for the transmission
of the ghost-canceling reference signal described in OET Bulletin No.
68, which is available from the FCC Warehouse, 9300 East Hampton Drive,
Capitol Heights, MD 20743. Notwithstanding the modulation limits
contained in paragraph (a)(23)(i) of this section, the vertical interval
reference signal formerly permitted on Line 19 and described in Figure
16 of Sec. 73.699, may be transmitted on any of lines 10 through 16
without specific Commission authorization, subject to the conditions
contained in paragraphs (a)(21)(ii) and (a)(22)(ii) of this section.
(22)(i) Line 21, in each field, may be used for the transmission of
a program-related data signal which, when decoded, provides a visual
depiction of information simultaneously being presented on the aural
Line 21, field 2 may be used for transmission of a program-related data
signal which, when decoded, identifies a rating level associated with
the current program. Such data signals shall conform to the format
described in figure 17 of Sec. 73.699 of this chapter, and may be
transmitted during all periods of regular operation. On a space
available basis, line 21 field 2 may also be used for text-mode data and
extended data service information.
Note: The signals on Fields 1 and 2 shall be distinct data streams,
for example, to supply captions in different languages or at different
EIA Television Systems Bulletin No. 1-EIA Recommended Practice of Use
of a Vertical Interval Reference (VIR) Signal, Electrical Industries
Association, Jul. 1972.
EIA Television Systems Bulletin No. 3-A History of the Vertical
Interval Color Reference Signal (VIR), Electrical Industries
Association, Mar. 1975.
And an interesting tutorial from someone's broadcast basics class:
More information about the Tig