Color gradation correction method and apparatus

A gradation correction apparatus for processing R, G, and B input signals, comprising:

• a luminance signal conversion means for obtaining the original luminance signal, which is before gamma conversion, from the input signals;
• a luminance gamma conversion means for gamma converting said original luminance signal to the desired gradation characteristics to obtain a gamma converted luminance signal;
• a correction coefficient calculation means for obtaining a ratio of the gamma converted luminance signal to the original luminance signal;
• a first RGB operation means for multiplying said ratio by each of the R, G, and B input signals for obtaining primary gradation-corrected R, G, and B signals;
• a color difference signal operation means for producing a difference between each of the R, G, and B input signals and the original luminance signal;
• a second RGB operation means for adding the gamma converted luminance signal to each of said difference for obtaining secondary gradation-corrected R, G, and B signals;
• and
• an RGB determination means for obtaining final gradation-corrected R, G, B signals based on said primary and secondary gradation-corrected R, G, and B signals.

A gradation correction method comprising the steps of:

• (a) obtaining an original luminance signal and first and second original color difference signals;
• (b) gamma converting said original luminance signal according to a predetermined gradation characteristics for obtaining a gamma converted luminance signal;
• (c) multiplying a ratio of the gamma converted luminance signal to the original luminance signal by each of the first and second original color difference signals for obtaining first and second primary gradation-corrected color difference signals;
• and
• (d) obtaining first and second final gradation-corrected color difference signals based on said first and second primary gradation-corrected color difference signals and said first and second original color difference signals.

A gradation correction method comprising the steps of:

• (a) obtaining an original luminance signal and two-phase modulated original chroma signal;
• (b) gamma converting said original luminance signal according to a predetermined gradation characteristics for obtaining a gamma converted luminance signal;
• (c) multiplying a ratio of the gamma converted luminance signal to the original luminance signal by said original chroma signal for obtaining a primary gradation-corrected chroma signal;
• and
• (d) obtaining final gradation-corrected chroma signal based on said primary gradation-corrected chroma signal and said original chroma signal.

A gradation correction apparatus for processing an input luminance signal and first and second input color difference signals comprising:

• a luminance gamma conversion means for gamma converting said input luminance signal to the desired gradation characteristics to obtain a gamma converted luminance signal;
• a correction coefficient calculation means for obtaining a ratio of the gamma converted luminance signal to the input luminance signal;
• a color difference conversion means for multiplying each of said first and second color difference signals by said ratio for obtaining first and second primary gradation-corrected color difference signals and
• a color difference determination means for obtaining first and second final gradation-corrected color difference signals based on said first and second primary gradation-corrected color difference signals and said first and second input color difference signals.

A gradation correction apparatus for processing an input luminance signal and an input chroma signal comprising:

• a luminance gamma conversion means for gamma converting said input luminance signal to the desired gradation characteristics to obtain a gamma converted luminance signal;
• a correction coefficient calculation means for obtaining a ratio of the gamma converted luminance signal to the input luminance signal;
• a chrominance conversion means for multiplying said input chroma signal with said ratio for obtaining primary gradation-corrected chroma signals;
• and
• a chrominance determination means for obtaining final gradation-corrected chroma signal based on said primary gradation-corrected chroma signal and said input chroma signal.