Abstract: Video signal sample data that has three values in one color space definition can produce values that are out of range in another color space definition, namely color gamut errors. The invention produces a polar plot with superimposed or added color difference and/or primary color values as a function of hue, as in a vectorscope, but values that when combined by conversion or transcoding may produce gamut errors are combined in the inventive display. Thus, excursion over or under a predetermined limit value identifies the gamut error. The display includes or is switchable between color difference and primary color color space definition variables.

Abstract: A video input signal is sampled and characterized in two different color space definitions, such as a color-difference color space and a primary-color color space. Certain values that are legal in one of the color spaces, for example the color difference space, can produce primary color amplitudes that are out of legal color gamut range. Such gamut violations are indicated according to the invention using a polar plot in which phase angle corresponds to hue as in a vectorscope. The color difference and/or primary color values in either or both color spaces are depicted as ranges of radii in the polar plot, which are compared to circular limit lines that can represent the legal gamut limits. In color difference color space, the signal excursion is plotted as a function of hue phase angle, producing radially inner and outer values in a plot. The excursion is calculated or processed as luminance plus and minus saturation as a function of hue phase angle.