Method and apparatus utilizing look-up tables for color graphics in the digital composite video domain

A method for utilizing look-up tables to create special color effects without decoding to luminance and chrominance, in a composite video system having a digitized composite video signal to be modified and said system capable of preserving or generating sync signals for later combination with the modified video signal, wherein said digitized video signal has discrete values having a sampling frequency Nf.sub.s where N is an integer greater than 1, and f.sub.s is the color subcarrier frequency of the video input signal, said method having the steps:

• a. Storing in memory having addressable storage locations N sets of up to b values where b is equal to the number of possible discrete values of the digitized video input signal, and where one value from each of the N sets is related to a specified value from each of the other sets to create b groups of N related values, where each group of N values represents successive values at N different points in time at equal periods of 1/Nf.sub.s in one complete cycle of the color subcarrier;
• b. Retrieving from memory the stored values at a rate Nf.sub.s and such that each of the N sets of values in memory is addressed in the predetermined order and using the digitized video input signal as addresses to the memory, to produce a digitized output signal having the same sampling rate as the digitized video input signal but with different values as desired.

A method for utilizing look-up tables to create special color effects without decoding to luminance and chrominance, in a composite video system having a digitized composite video signal to be modified and said system capable of preserving or generating sync signals for later combination with the modified video signal, wherein said digitized video signal has discrete values having a sampling frequency Nf.sub.s where N is an integer greater than 1, and f.sub.s is the color subcarrier frequency of the video input signal, said method having the steps:

• a. Creating one or more groups of N values to be stored and retrieved from memory, one group for each color to be displayed, by determining the amplitude values necessary at each of N successive points in equal periods of 1/Nf.sub.s on a wave of one cycle of a color subcarrier of frequency f.sub.s such that when the values are sampled in the desired predetermined order at a rate Nf.sub.s and filtered, a full cycle of the color subcarrier having the phase and amplitude characteristics necessary to produce the desired color to be displayed for each group will result;
• b. Storing in memory the groups of N values in various locations in memory so that each group of N values will be retrievable in response to a selected level of the amplitude of the composite video input signal, and such that the N values in each group will be retrievable in the predetermined order necessary to produce the desired color;
• c. Retrieving from memory the stored values in response to the composite video input signal, such that for desired levels of the video input signal, the group stored corresponding to said level will be retrieved, and so that the N values in each group so retrieved will be retrieved in the predetermined order, to produce a digitized video output signal responsive to the video input signal but with different values as desired.

Apparatus for utilizing look-up tables to create special color effects without decoding to luminance and chrominance, in a composite video system having a digitized composite video signal to be modified, wherein said digitized video signal has discrete values having a sampling frequency Nf.sub.s where N is an integer greater than 1, and f.sub.s is the color subcarrier frequency of the video input signal, said apparatus comprised of:

• a. Memory means having addressable storage locations;
• b. Means for creating one or more groups of N values to be stored in and retrieved from said memory means, one group for each color to be displayed, by determining the amplitude values necessary at each of N successive points in equal periods of 1/Nf.sub.s of a wave of one cycle of a color subcarrier of frequency f.sub.s such that when the values are accessed in the desired predetermined order at a rate Nf.sub.s and filtered, a full cycle of the color subcarrier having the phase and amplitude characteristics necessary to produce the desired color to be displayed for each group will result;
• c. Means for storing in memory the groups of N values in various locations in memory so that each group of N values will be retrievable in response to a selected level of the amplitude of the composite video input signal, and such that the N values in each group will be retrievable in the predetermined order necessary to produce the desired color;
• d. Means for retrieving from said memory means the stored values in response to the composite video input signal, such that for desired levels of the video input signal, the group stored corresponding to said level will be retrieved, and so that the N values in each group so retrieved will be retrieved in the predetermined order, to produce a digitized video output signal responsive to the video input signal but with different values as desired.