Color Bars
Color Bars – A video test signal widely used for system and monitor setup. The test signal, typically containing eight basic colors: white, yellow, cyan, green, magenta, red, blue and black, is used to check chrominance functions of color TV systems. There are two basic types of color bar signals in common use. The terms “75% bars” and “100% bars” are generally used to distinguish between the two types. While this terminology is widely used, there is often confusion about exactly which parameters the 75% versus 100% notation refer to. a) RGB Amplitudes – The 75%/100% nomenclature specifically refers to the maximum amplitudes reached by the Red, Green and Blue signals when hey form the six primary and secondary colors required for color bars. For 75% bars, the maximum amplitude of the RGB signals is 75% of the peak white level. For 100% bars, the RGB signals can extend up to 100% of peak white. Refer to the following two figures. b) Saturation – Both 75% and 100% amplitude color bars are 100% saturated. In the RGB format, colors are saturated if at least one of the primaries is at zero. Note: In the two associated figures that the zero signal level is at setup (7.5 IRE) for NTSC. c) The Composite Signal – In the composite signal, both chrominance and luminance amplitudes vary according to the 75%/100% distinction. However, the ratio between chrominance and luminance amplitudes remains constant in order to maintain 100% saturation. d) White Bar Levels – Color bar signals can also have different white bar levels, typically either 75% or 100%. This parameter is completely independent of the 75%/100% amplitude distinction and either white level may be associated with either type of bars. e) Effects of Setup – Because of setup, the 75% signal level for NTSC is at 77 IRE. The maximum available signal amplitude is 100-7.5 or 92.5 IRE. 75% of 92.5 IRE is 69.4 IRE, which when added to the 7.5 IRE pedestal yields a level of approximately 77 IRE. 1
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