ITU-R BT.656 是 ITU-R BT.601的延伸.
這兩種標準都是 video transmission 的 interface，在 video frame format 的規格是相同的，也就是每張 frame 是 720x480， YUV 4:2:2 的格式，兩者的差別在於 interface 規格的不同，在 CCIR656 中，有 8 bit 的 data bus 和 clock 的訊號，也就是說 CCIR656 是同步傳輸的，decoder 端不用自己產生 clock。在 CCIR601 中，訊號內包含了兩個同步訊號, HSYNC 和 VSYNC。
1. 基本上 CCIR 656 的 CLK 為 27M Hz, DataBus 為 8Bits. CCIR 601 的 CLK 為 13.5M Hz，VIeX
Data 為 16Bits.但兩者同為 YUV4:2:2,所以品質是相同的,CCIR 656 需要 9Pins、CCIR 601 3" 9G
需要 19Pins,所以 CCIR 656 DATABUS 較省,但 CLK 較快。
2. CCIR 656 收到 DATA 後需轉換成 CCIR 601 後再轉換成 YUV4:4:4,且 CLK 需除頻(/2)為 13.5M Hz；CCIR601 直接將 DATA 轉換成 4:4:4 即可, CLK 不變。
3. CCIR 656 需從 DATA 中解出 VS、HS, CCIR 601 則直接使用輸入的 VS、HS 即可
4. 由於 CCIR 656 PIN 腳較少且 27M Hz 的 CLK 對現在的 IC 根本不算快,所以使用 CCIR 656 可能
會比較適合.
CCIR 601 is the old name of a standard published by the CCIR (now ITU-R) for encoding interlaced analogue video signals in digital form. It includes methods of encoding 525-line 60 Hz and 625-line 50 Hz signals, both with 720 luminance samples and 360 chrominance samples per line. The colour encoding system is known as 4:2:2, that being the ratio of Y:Cb:Cr samples (luminance data:blue chroma data:red chroma data). For a pair of pixels, the data is stored in the order Y1:Y2:Cb:Cr, with the chrominance samples co-sited with the first luminance sample.
The CCIR 601 signal can be reagarded as if it is a digitally encoded analog component video signal, and thus includes data for the horizontal and vertical sync and blanking intervals. Regardless of the frame rate, the luminance sampling frequency is 13.5 MHz. The luminance sample is at least 8 bits, and the chrominance samples are at least 4 bits each.
The first version of CCIR 601 defined only a parallel interface, but later versions introduced the bit-serial versions that are now commonly used. The 8-bit serial protocol (216 Mb/s) was once used in D1 digital tape recording. Modern standards use an encoding table to expand the data to 9 or 10 bits. The 9-bit serial version has a data rate of 243 Mb/s. The 10-bit version used in D5 digital tape recording has a data rate of 270 Mbits/s.
There is an 8-bit version in which only data from the active video periods are transmitted, with a bit rate of only 165.9 Mbit/s.
In each 8-bit luminance sample, the value 16 is used for black and 235 for white, to allow for overshoot and undershoot. The values 0 and 255 are used for sync encoding. The Cb and Cr samples use the value 128 to encode a zero value, as used when encoding a colourless area.
The CCIR 601 video raster format has been re-used in a number of later standards, including MPEG.
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Simply speaking, CCIR601 defines the sampling systems, matrix values and filter characteristics for both (Y/B-Y/R-Y) and (R/G/B) component of digital television signals.
CCIR656 is "the physical parallel and serial interconnect scheme for CCIR601". CCIR656 defines the parallel connector pinouts as well as the blanking, sync, and multiplexing schemes used in both parallel and serial interface.
引用 看盡洛城花