Ccir601 and ccir656 standards

Ccir601 and ccir656 standards

CCIR (Consultative Committee of International Radio)

Chinese Translation: International Radio Advisory Committee

Classification: Others

Interpretation: CCIR is short for the international radio Advisory Committee. Founded in 1927, it is one of the permanent institutions of the International Telecommunication Union (ITU. It is mainly responsible for researching wireless communication and technology business issues and adopting proposals for such issues.

Since March 1, 1993, it has been integrated with the ifrb to become the Radio Communication Department of the International Telecommunication Union (ITU.

The difference between the two signals: ITU-R BT 601: 16-bit data transmission; 21-core; y, U, V signal transmission at the same time.

ITU-R BT 656: 9-core, no need for synchronous signal; 8-bit data transmission; Serial video transmission; transmission rate is 2 times of 601; first pass y, then pass UV.

656 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 row-field synchronization has a separate output;

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 chips) A digital transmission interface standard that uses a 27 MHz/S parallel port or a 243 Mbit/s serial interface.

The formulation of ccir601 proposal is the first step towards the unification and standardization of digital television broadcasting system parameters. In this suggestion, the basic parameter values of the digital encoding of the TV Center studio of the 625 and 525 lines system are specified.

The coding standard of the TV studio is specified separately in the Recommendation No. 601. It specifies the encoding method, sampling frequency, and sampling structure of color TV signals.

It specifies that the color TV signal uses component encoding. The so-called component encoding means that a color TV signal is first separated into a brightness signal and a chromatic aberration signal before being converted into a digital form, and then encoded separately. The component signal (Y, B -- y, r -- Y) is encoded separately, and then the digital signal is synthesized. It specifies 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.

 

Digital Video CCIR 601 encoding standard

I. 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 FS frequency, and the two chromatic aberration signals are respectively used

F S/2 = 6.75mhz frequency sampling. The minimum sampling rate of the color component is 3.375 MHz.

Ii. Resolution: According to the sampling frequency, 864 sample points are sampled for each scan row in the PAL and SECAM formats. For NTSC, 858 sample points are sampled. Since 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 all the standard, 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 the basic standard for High Definition TV (High Definition TV) by 720 × 484. When a digital video is displayed on a computer, the following parameters are usually used:

TV System
 
Resolution
 
Frame Rate

NTSC
 
640 × 480
 
30

Pal, SECAM
 
768 × 576
 
25

Iii. Data volume: CCIR 601 specifies 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 can also be calculated. If sampling is performed, the data size of a digital video is 40 MB per second! Based on the data rate of 27 MB per second, a 10-second digital video occupies 270 MB of storage space. Based on this data rate, a 680 MB optical disk can only record information about 25 seconds of digital video data, and even if the current high-speed optical drive, the data transmission rate is far from 27 MB per second, and video data cannot be played back in real time. This Uncompressed Digital Video data volume is unrealistic for current computers and networks, whether stored or transmitted. Therefore, the key issue of digital video application in multimedia is digital video compression technology.