电视设计基础

Video System and Video Processing
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Human visual perception in TV •Human visual perception to Red, Green ,Blue The major light sensing element in the human eye is the retina. The retina consists of the major light receptors ---rods and cones which at the bottom of the retina.Image is formed by the light that reaching the main photoreceptors. Research shows that red, green and blue colors are the primary colors, as "If you mix light of these colors together you can make any color". They lie in the nature of the human eye. Some colors could have by following experiments :
Basic TV Course
Video System and Video Processing
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Frame scanning in TV
• Interlaced Frame Scan first field start second field start Screen frame
Fig. Interlacing lines Basic TV Course Video System and Video Processing 5
Scanning Control
Synchronization Processor
Fig. Basic TV system
Sync Separation
H/V pulse
Synchronization processor
H/V drive
Deflection & EHT. Generation
Basic TV Course
Projector screen
Basic TV Course
Video System and Video Processing
3
Human visual perception in TV •Understanding of visual persistence with human vision The human eye retains an image for a fraction of a second after it views the image. This property (called persistence of ຫໍສະໝຸດ Baiduision) is essential to all visual display technologies. The still images are presented at a high enough frame repetition rate so that persistence of vision integrates these still images into motion. For some reason, The motion pictures was found to be unacceptable when image repetition rate is below 48 frames per second. Therefor to realize the repetition rate of 48 frame per second, in the television system one picture frame is splited into two fields, and the field frequency is defined as 50Hz or 60Hz (higher than 48Hz) determined by the video system. 50Hz/60Hz field repetition rate gives normal perception to the image on TV screen. The idea is that a single frame is scanned twice(see Fig. Interlacing lines). The first field scan includes only the odd lines, the next field scan includes only the even lines. With this method, the number of "flashes" per frame is two, and the field rate is just double the frame rate so that 50hz/60hz field rate has their frame rate at 25/30Hz in TV. The 50Hz field scan system contains 625 horizontal lines per frame and each field scans 312.5 lines. The 60Hz field scan system contains 525 lines per frame, each field scans 262.5 lines.
Synchronization components of video signal
•Video signals during blanking period Timing of scanning is arranged by the sync pulses. Each field scan
starts with a vertical sync, each line scan starts with a horizontal pulse. The horizontal and vertical blanking period are specified around the sync pulses. With blanking period the electron beam complete its fly-back from the right to the left for horizontal scan or from the bottom to the top of screen for field scan. During the period the electron beam is cutoff, so that no scan line is visible on the screen.The combination of horizontal blanking signal and synchronization pulse is defined as illustrated in Fig. Sync Signal during horizontal blanking period . For color signals, a so called „color burst‟ is inserted onto the "back porch”of the H sync, that carries the color system info.for use in color decoder(more on this later). The burst period is about 8-10 cycle time of the sub-carrier (info.)
sequence first field start second field start Screen frame
Fig. Demonstration of real scanning sequence Basic TV Course Video System and Video Processing 6
H/V Sync pulse
Receiver
Tuner&IF Demodulator
prism
R/G/B
CVBS
Source Selection Video Processing
R/G/B
C
R/G/B Driver
Scan Current
Blanking pulse
CVBS
Scan current
EHT
Basic TV Course
Video and Synchronization Processing
List of content
•Basic Function Block of TV system •Human vision in TV & Interlacing scan •Synchronization processing in TV
–Phase-1 loop / Phase-2 loop / Sandcastle
•CVBS signal & World conventional color TV standard
–NTSC / PAL / SECAM
•PAL / NTSC / SECAM Video Signal encoding
Frame scanning in TV
•Presentation of interlacing scanning In a TV, the electron beam is used to scan a phosphor screen. The
scan is interlaced.For each horizontal line scan the information is always displayed from left to right, after each line is written, the signal is blanked, the beam starts returning back to the left. When the signal reached the bottom it is blanked until it returns to the top to write the first line in next field. the beam does not return directly to the top, but zig-zags route. See Fig. Demonstration of real scanning
•PAL/ NTSC/ SECAM System decoding •Luminance Signal processing as picture improvement –Peaking / LTI / CTI –Signal level stretch: Black / Blue / White level –Soft Clipping / Peak White Limiting –Histogram
Prepared by: Wang Guo Ji
Basic TV Course Video System and Video Processing
Oct 2000
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Function Block of Video System
Transmission IF&RF modulator
•Gamma correction/ Video encoder
Fig. 50Hz Sync Signal during horizontal blanking period Basic TV Course Video System and Video Processing 7