AV4 - Efficient use of spectrum Less sensitive to noise&...

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Unformatted text preview: Efficient use of spectrum Less sensitive to noise & distortions Integration of digital services Data Encryption Digital Video 576 lines 5.5MHz = 720 pixels Raw image 576 lines/frame 720 pixels/line 50 fields/second 8 bit per pixel Total: 576x720x25x3 x8 = 249Mbit/sec R , G and B R: 83Mbit/s G: 83Mbit/s B: 83Mbit/s Total: 249Mbit/s Figure 2a f VSB Chroma at 4.43 MHz-1.75 MHz Sound at 6 MHz Chrominance can be represented with a considerable narrower bandwidth (resolution) than luminance 576 lines 5. 5MHz = 720 pixels PAL system 576 lines/frame 720 pixels/line 50 fields/second 8 bit per pixel Total: 576x720x25x8 = 83Mbit/sec Luminance Y Y: 83Mbit/s U: V: Total: Figure 2b 288 lines 2.75MHz = 360 pixels PAL system 288 lines/frame 360 pixels/line 50 fields/second 8 bit per pixel Total: 288x360x25x8 = 21Mbit/sec Chrominance U Y: 83Mbit/s U: 21Mbit/s V: Total: Figure 2c 288 lines 2.75MHz = 360 pixels PAL system 288 lines/frame 360 pixels/line 50 fields/second 8 bit per pixel Total: 288x360x25x8 = 21Mbit/sec Chrominance V Y: 83Mbit/s U: 21Mbit/s V: 21Mbit/s Total: 125Mbit/s Figure 2d Medium Quality : 1.2 Mbit/s Superior Quality : 6 Mbit/s Actual size - 249Mbit/s Result: Compression is necessary U,V downsampled - 125Mbit/s Redundancy in image contents Adjacent pixels are similar Intensity variations can be predicted Sequential frames are similar Lossy compression: Removal of redundant information, resulting in distortion that is insensitive to Human Perception Figure 3a Lenna Pixels within this region have similar but not totally identical intensity. Figure 3b Figure 3b Intensity position 1 2 3 4 5-1-2-3-4-5 Autocorrelation function 0.2 0.4 0.6 0.8 1.0 Figure 4 Interpolation 1. Pixel intensities usually varies in a smooth manner except at edge (dominant/salient) points 2. Record pixels at dominant points only. 3. Reconstruct the pixels between dominant points with “Interpolation”. 4. A straightforward method: Joining dominant points with straight lines. 5. High compression ratio for smooth varying intensity profile. 6. Difficulty: How to identify dominant points? Intensity position Figure 5a Transmit only selected pixels predicted the rest Prediction of current sample based on previous ones ∑ Quantizer ( Q ) Predictor ( P ) ∑ + + +-( 29 n x ( 29 n x ˆ ( 29 n e p ( 29 n x p ( 29 n e pq Input signal ( 29 n x Predicted signal ( 29 n x p Error signal ( 29 ( 29 ( 29 n x n x n e p p-= Quantized error signal ( 29 n e pq Reconstructed signal ( 29 ( 29 ( 29 n e n x n x pq p + = ˆ Quantizer: representation of a continuous dynamic range with a finite number of discrete levels (will be discussed later) Error = Quantization error Function of Predictive Coding: Data Compression ∑ Quantizer ( Q ) Predictor ( P ) ∑ + + +-( 29 n x ( 29 n x ˆ ( 29 n e p ( 29 n x p ( 29 n e pq ( 29 [ ] 243 199 162 120 81 40 , , , , , , = n x p ( 29 [ ] 241 198 163 119 82 41 , , , , , , = n x 8 bits The better the predictor, the higher is the...
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AV4 - Efficient use of spectrum Less sensitive to noise&...

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