In the Digital Production Center, many of the videotapes we digitize have “bars and tone” at the beginning of the tape. These are officially called “SMPTE color bars.” SMPTE stands for The Society of Motion Picture and Television Engineers, the organization that established the color bars as the North American video standard, beginning in the 1970s. In addition to the color bars presented visually, there is an audio tone that is emitted from the videotape at the same time, thus the phrase “bars and tone.”
The purpose of bars and tone is to serve as a reference or target for the calibration of color and audio levels coming from the videotape during transmission. The color bars are presented at 75% intensity. The audio tone is a 1kHz sine wave. In the DPC, we can make adjustments to the incoming signal, in order to bring the target values into specification. This is done by monitoring the vectorscope output, and the audio levels. Below, you can see the color bars are in proper alignment on the DPC’s vectorscope readout, after initial adjustment.
We use Blackmagic Design’s SmartView monitors to check the vectorscope, as well as waveform and audio levels. The SmartView is an updated, more compact and lightweight version of the older, analog equipment traditionally used in television studios. The Smartview monitors are integrated into our video rack system, along with other video digitization equipment, and numerous videotape decks.
If you are old enough to have grown up in the black and white television era, you may recognize this old TV test pattern, commonly referred to as the “Indian-head test pattern.” This often appeared just before a TV station began broadcasting in the morning, and again right after the station signed off at night. The design was introduced in 1939 by RCA. The “Indian-head” image was integrated into a pattern of lines and shapes that television engineers used to calibrate broadcast equipment. Because the illustration of the Native American chief contained identifiable shades of gray, and had fine detail in the feathers of the headdress, it was ideal for adjusting brightness and contrast.
When color television debuted in the 1960’s, the “Indian-head test pattern” was replaced with a test card showing color bars, a precursor to the SMPTE color bars. Today, the “Indian-head test pattern” is remembered nostalgically, as a symbol of the advent of television, and as a unique piece of Americana. The master art for the test pattern was discovered in an RCA dumpster in 1970, and has since been sold to a private collector. In 2009, when all U.S. television stations were required to end their analog signal transmission, many of the stations used the Indian-head test pattern as their final analog broadcast image.
2 thoughts on “Color Bars & Test Patterns”
I’m from Detroit, looking forward to visiting on site and the libraries
This is interesting. Do you have any idea why they chose an Indian Head for the image? Why not an animal or a flag or anything else?
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