Introduction to ITU-R bt.601

Introduction to ITU-R bt.601

In 1982, CCIR (International Radio Consultative Committee International Radio Advisory Committee) developed the color video digitization standard, known as the CCIR 601 standard, and is now changed to the ITU-R bt.601 standard (601-4: 1994.7. /601-5: 1995.10 ). This Standard specifies the sampling frequency used to convert a color video to a digital image, and the conversion relationship between two color spaces: RGB and YCbCr. Among them, ITU = International Telecommunication Union (United Nations) International Telecommunication Union, r = Radiocommunication Sector radio department, bt = Broadcasting Service (television) broadcast service (TV ). In order to facilitate international program exchange, to eliminate the standard differences between digital devices, and to ensure compatibility between the 625-line TV System and the 525-line TV system, the digital television broadcasting system parameters are unified and standardized, at the 15th plenary meeting of the International Radio Advisory Committee (CCIR) on February 1982, Recommendation No. 601 was adopted to determine the basis of the component code, that is, the brightness component y, and two color components r-y, B-Y as the basis for encoding,International standards for Digital Coding in TV studios,The coding standard of the TV studio is specified separately in the Recommendation No. 601. This standard stipulates: (1) Whether it is paled or ntsc TV, Y, r-y, B-Y three-point sampling frequency were 13.5 MHz, 6.75 MHz, 6.75 MHz. (2) linear quantization is used after sampling. The quantified bits of each sample point are used for 10 bits in the studio and 8 bits for transmission. (3). Y, r-y, B-Y three points between the ratio of 4: 2: 2. At the interim meeting of the International Radio Advisory Committee (CCIR) held on September 1983Three supplements: (1) clearly stipulate that the encoding signal is pre-corrected by gamma y, (R-Y), B-Y) signal; (2). Code words corresponding to the quantization level 0 and 255 are used for synchronization, And the quantization level from L to 254 is used for video signals; (3 ). the correspondence between the simulation and the number row is further clarified, and the interval from the end of the Number Valid row to the reference time sample is defined. For the standard of 525 rows and 60 fields/second, 16 samples are provided, for 625 rows and 50 fields/second, 12 samples are displayed. No matter 625 rows/50 rows or 525 rows/60 rows, the brightness sample points of the valid numeric rows are 720, and the sample points of the chromatic aberration signal are 360, so as to facilitate standard conversion. If the number of brightness samples is divided by two, the data of the chromatic aberration signal is obtained. Meanings The sampling frequency of the Brightness Signal is 13.5 MHz, and the sampling frequency of each chromatic aberration signal is 6.75 MHz. The sampling frequency ratio is, or, the number of sampling points for each valid line Brightness Signal is 720, and the number of sampling points for each chromatic aberration signal is 360. The ratio of sampling points is also, this is the standard for digital component encoding, also known as the format. It is used as a digital standard for studio Digital Equipment and Its connection or International Program Exchange. 1.1 sampling frequency To ensure signal synchronization, the sampling frequency must be a multiple of the television signal frequency. CCIR is a common TV image sampling standard developed for NTSC, pal, and SECAM: F S = 13.5 MHz The sampling frequency is exactly 864 times of the PAL and SECAM line frequency, and 858 times of the NTSC line frequency. This ensures that the sampling clock is synchronized with the line synchronization signal during sampling. For the sampling format at, the Brightness Signal is sampled at a frequency of 13.5mhz, and the two chromatic aberration signals are sampled at a frequency of f S/2 = 6.75mhz, respectively. In addition to the standard, the sampling frequency of the chromatic aberration signal is also set to the lower standard and at 3.375mhz. In addition, for higher image quality requirements, the sampling frequency of chromatic aberration signals is set to a higher standard of at 13.5mhz. 1.2 resolution According to the sampling frequency, 864 sample points can be sampled for the PAL and SECAM systems, and 858 sample points can be sampled for each scan line. For the NTSC system, the sample points are. Because each line of the TV signal includes a certain synchronous signal and a return signal, there are not so many valid image signal sample points,CCIR 601 specifies that for all standards, the valid sample points for each row are 720 points. The number of valid lines per frame varies according to different standards (PAL and SECAM are 576 rows, and NTSC is 484 rows ),CCIR defines 720x484 for High Definition TV hdtv (High Definition TV Definition TV) Basic Standards. ActualComputerWhen displaying a digital video, the following parameters are usually used: TV System Resolution Frame Rate (frame/s) NTSC 640 × 480 25 Pal, SECAM 768 × 576 30 1.3 Data Volume CCIR 601 stipulates that each sample point is digitalized in 8 bits, that is, there are 256 levels. However, in fact, the Brightness Signal accounts for 220, the color signal accounts for 225, and other bits are used for synchronization, encoding, and other control. If the sampling rate is f s and the format is, the data volume of the digital video is: 13.5 (MHz) × 8 (BIT) + 2 × 6.75 (MHz) × 8 (BIT) = 27 MByte/s The bit rate and minimum compression ratio of different color sampling formats and different resolutions are calculated as follows: A) 4: 2 format 　　The pixel rate of sdtv is :(720 × 576 + 2 × 360 × 576) × 25 = (720 × 480 + 2 × 360 × 480) × 30 = 20.736 MB pixel/second Bit Rate = 20.736 Mbit/s x 8 bit = 165.888 Mbps In the main level video format, the maximum transmission rate is 15 Mbps, and the minimum compression ratio is 165.888 Mbps/15 Mbps = 11.06. 　　The pixel rate of the narrow screen HDTV is :(1440 × 1152 + 2 × 720 × 1152) × 25 = (1440 × 960 + 2 × 720 × 960) × 30 = 82.944 MB pixel/second Bit Rate = 82.944 Mbit/s x 8 bit = 663.552 Mbit/s. If the highest Transmission Bit Rate of the High-1440 level is 60 Mbps, the minimum compression ratio is 663.552 Mbps/60 Mbps = 11.06. 　　The pixel rate of the wide screen HDTV is :(1920 × 1152 + 2 × 960 × 1152) × 25 = (1920 × 960 + 2 × 960 × 960) × 30 = 110.592 MB pixel/second Bit Rate = 110.592 Mbit/s x 8 bit = 884.736 Mbps If the highest Transmission Bit Rate of the High Level is 80 Mbps, the minimum compression ratio is 884.736 Mbps/80 Mbps = 11.06. B) format Because the human eye is not sensitive to the color definition, the format can be used to reduce the bit rate. The bit rate and minimum compression ratio of each video format are as follows: 　　The pixel rate of sdtv is :(720 × 576 + 2 × 360 × 288) × 25 = (720 × 480 + 2 × 360 × 240) × 30 = 15.552 MB pixel/second Bit Rate = 15.552 Mbit/s x 8 bit = 124.416 Mbps Compression rate = 124.416 Mbps/15 Mbps = 8.29 　　The pixel rate of the narrow screen HDTV is :(1440 × 1152 + 2 × 720 × 576) × 25 = (1440 × 960 + 2 × 720 × 480) × 30 = 62.208 MB pixel/second Bit Rate = 62.208 Mbit/s x 8 bit = 497.644 Mbps Compression ratio = 497.664 Mbps/60 Mbps = 8.29 　　The pixel rate of the wide screen HDTV is :(1920 × 1152 + 2 × 960 × 576) × 25 = (1920 × 960 + 2 × 960 × 480) × 30 = 82.944 MB pixel/second Bit Rate = 82.944 Mbit/s x 8 bit = 663.552 Mbps Compression ratio = 663.552 Mbps/80 Mbps = 8.29 601 set the sampling frequency and structure: For example, in the encoding, the sampling frequency of the specified Brightness Signal and chromatic aberration signal is 13.5mhz and 6.75 MHz, respectively, and the sampling structure is orthogonal, that is, the sampling structure is repeated by line, field, and frame, r-Y and B-Y sampling per line with odd times (1, 3, 5 ......) Y sampling is at the same position, that is, the sampling structure is fixed, and the relative position of the sampling point on the TV screen remains unchanged. It specifies the encoding method. Linear PCM encoding is performed on the Brightness Signal and two chromatic aberration signals. 8 bits are used to quantify each sampling point. At the same time, it is stipulated that the entire dynamic range of A/D conversion is not used during digital encoding, and only 220 quantization levels are allocated to the brightness signal. The black level corresponds to the quantization level 16, the white level corresponds to the quantitative level of 235. Assign 224 quantization levels for each chromatic aberration signal. The zero level of the chromatic aberration signal corresponds to a quantization level of 128. To sum up, we know that the encoding data stream of the component signal is very high. Taking the encoding standard as an example, the bit stream is 13.5 × 8 + 6.75 × 8 × 2 = 216 Mb/s. If the 4: 4 encoding method is used, that is, the compound signal is directly encoded, and the sampling frequency is 13.3 × 8 = 106.4 Mb/s. 2. Difference Between ITU-R bt.601 and ITU-R bt.656 Differences between the two signals: ITU-R BT 601:16-bit data transmission; 21-core; y, U, V signal transmission at the same time, the last updated document code: ITU-R BT.601-5. ITU-R BT 656:9-core, no synchronous signal; 8-bit data transmission; Serial video transmission; transmission rate is twice the rate of 601; first transfer y, then pass UV. 656 of the output is serial data, and the synchronous signal of the line field is embedded in the data stream. 601 is parallel data, and the synchronous line field has a separate output. The last updated document code is the ITU-R BT.656-4. 656 is only a data transmission interface. It can be said that it is used as a transmission method of 601. Simply put, ITU-R bt.601 is "Studio digital TV encoding Parameters" standard, while ITU-R bt.656 is the digital interface standard in ITU-R bt.601 Attachment A, used for main digital video equipment (including core) uses a 27 MHz/S parallel port or a 243 Mbit/s serial interface.