he items in the table. Vertical lines refers to the number of active lines in the picture. Pixels are the number of pixels during the active line. Aspect ratio, of course, refers to the picture aspect ratio. Picture rate gives the number of frames or fields per second. Regarding picture rate values, P refers to progressive scanning and I refers to interlaced scanning. It should be noted that both the 60.00-Hz and 59.95 (i.e., 60 X 1000/1001)-Hz picture rates are allowed. Dual rates are permitted at 30 Hz and 24 Hz. Sampling Rates. Three active line formats are considered: 1080, 720, and 483. Table 16.5 summarizes the sampling rates. For the 480-line format, there may be 704 or 640 pixels in an active line. If the input is based on ITU-R Rec. BT 601-4 (Ref. 19), it will have 483 active lines with 720 pixels in each active line. Only 480 of the 483 active lines are used for encoding. Only 704 of the 720 pixels are used for encoding: the first eight and the last eight are dropped. The 480-line, 640-pixel format corresponds only to the IBM VGA graphics format and may be used with ITU-R Rec. BT 601-4 (Ref. 19) sources by employing appropriate resampling techniques. Sampling precision is based on the 8-bit sample. Colorimetry means the combination of color primaries, transfer characteristics, and matrix coefficients. The standard accepts colorimetry that conforms to SMPTE.9 Video inputs corresponding to ITU-R Rec. BT 601-4 may have SMPTE 274 M or 170 M col- orimetry. The input video consists of the RGB components that are matrixed into luminance (Y) and chrominance (Cb and Cr) components using a linear transformation by means of a 3 X 3 matrix. Of course, the luminance carries picture intensity information (black- and-white) and the chrominance components contain the color. There is a high degree of correlation of the original RGB components, whereas the resulting Y, Cb, and Cr have less correlation and can be coded efficiently. Table 16.5 Sampling Rate Summary Total Lines Total Samples Sampling Line Format per Frame p