Logarithmic color matrix for a digital television receiver

Abstract

In a digital television receiver, a signal processing stage generates color mixture digital signals representing color picture information as components in a first color mixture coordinate system such as the I-Q system. The I and Q digital signals are applied to a read only memory look-up table in which memory locations are stored the logarithmic values of the signals in order to convert the signals into digital words represented in logarithmic form. A microprocessor or other digital circuit generates or retrieves digital coefficients in logarithmic form that enable the I and Q digital signals to be transformed into second color mixture digital signals representing the color picture information as components in a second color mixture coordinate system such as the R-Y, B-Y, color difference coordinate system. The I and Q digital signals in logarithmic form are applied to a first input of an adder. A digital store stores the coefficients, and a multiplexer coupled to the digital store supplies to a second input of the adder a sequence of coefficients in the same order corresponding to the sequence of I and Q digital signals being applied to the first input of the adder. At the output of the adder there is developed a plurality of products in logarithmic form that correspond to the values of the I and Q constituents of the R-Y, B-Y digital signals. The plurality of products are applied to an antilog read only memory look-up table in which memory locations are stored the inverse logarithmic values of the I and Q constituents. A second adder receives the output of the antilog ROM, now in straight arithmetic form, to obtain the R-Y, B-Y or G-Y color difference signals.