ITU656信号解析.docxVIP

A Brief Introduction to Digital VideoThis page provides a brief introduction to the BT656 (4:2:2) YCbCr Standard Definition 8-bit Digital Video format. By no means does it describe the full video standard in detail, it mealy introduces the subject matter from an implementation perspective.?FramesA full frame of interlaced video consists of two almost identical fields. The first field contains all the odd video lines and the second field contains all the even video lines.?FieldsA field is made up of three distinct regions, first blanking period, active video and second blanking period. The difference between the first field and the second, is merely in the number lines during the first blanking period, the first field having one less than the second.?A complete NTSC/PAL video frame (both fields) is shown below: -?LinesField / VBlkLineDescriptionPALNTSCFV221901Field 1 - First Vertical Blanking (Topield 1 - Active Video2301Field 1 - Second Vertical Blanking (Bottom)232011Field 2 - First Vertical Blanking (Topield 2 - Active Video2311Field 2 - Second Vertical Blanking (Bottom)625525There are two very important values to remember here, these being F (Field Number) and V (Vertical Blanking). These values control the vertical position of a line.?A logic zero on F states that a line belongs in Field 1, likewise a logic one on F states that a line belongs in Field 2.?A logic zero on V states that a line is part of the Active Video, whereas a logic one on V states that a line is part of the Vertical Blanking.?LinesLines consist of four parts, EAV Code, Blanking Video, SAV Code and Active Video. These are shown below: -?EAV CodeBlanking VideoSAV CodeActive Video25500EAVCbYCrY25500SAVCbYCrY4 Bytes280 (268) Bytes4 Bytes1440 BytesThe EAV (End Active Video) and SAV (Start Active Video) Codes are made up of four bytes. The first three bytes provide the video synchronization and the last one byte provides the line coding.?What has not been discussed so far is H,