(4-1-1) This is a set of sampling frequencies in the ratio 4:1:1, used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. The four represents 13.5 MHz, the sampling frequency of Y, and the ones each 3.75 MHz for R-Y and B-Y. With the color information sampled at half the rate of the 4:2:2 system, this is generally used as a more economical form of sampling for 525-line picture formats. Both luminance and color difference are still sampled on every line. But the latter has half the horizontal resolution of 4:2:2, while the vertical resolution of the color information is maintained. For 525-line pictures, this means the color is fairly equally resolved in horizontal and vertical directions.