Figure 2 DCT basis functions standards. Figure 4 MPEG Group Of Pictures structure quence for applications that require random access. Figure 5 Structure of MPEG bitstream these experiments is shown in Figure 6. Table 2 Visual quality grading scale Each observer is presented with a set of video sequences including reference sequences and More detailed cell loss models can be found in the literature, for example see papers in by the mean burst length. Figure 13 Error spreading due to motion compensation of each B-picture is about 2-3dB lower than that of its neighbouring I/P-pictures. Figure 15 PSNR of error-free decoded sequence Figure 16 PSNR drop due to error in I-picture Figure 17 PSNR drop due to error in 1* P-picture in a GOP, and in Figure 19, where the cell loss occurs in the 3rd and final P-picture in a drop due to cell loss in an I or P-picture. Figure 20 PSNR drop due to error in B-picture value are shown in Figure 20. The average is just over 3dB, significantly lower than the Figure 21 PSNR of error-free and errored sequences Figure 22 Drop in PSNR relative to error-free sequence frames in the decoded sequence is 36.3 dB. Figure 23 Quality loss due to bit errors (Graduation) Figure 24 PSNR of decoded MPEG video: bit errors (Nursery) quality drops significantly. Figure 25 Quality loss due to cell losses (Graduation) Figure 26 PSNR of decoded MPEG video: cell losses (Nursery) contains less detail. (mainly P-pictures) and a smaller number between 250-400 cells (mainly I-pictures). Figure 28 Probability distribution Figure 29 Contents of "leaky bucket": leak rate = 2 x MCR “burst” of cells, causing the bucket to fill up rapidly. Figure 30 Contents of "leaky bucket": leak rate=1.2 x MCR which cells arrive has dropped. Table 3 Cell loss effects on decoded video (leak rate = 2 x mean cell rate) of values from 160 (highest number of lost cells) to 220 (lowest number of lost cells). Figure 32 Leaky bucket contents with adaptive rate control reduced variation in data rate compared to the unconstrained data rate shown in Figure 27. Figure 34 Quantization step size Figure 34 shows how the quantization step size varies during the sequence. Figure 35 Bit rate variation (JPEG encoding) Figure 36 Bit rate variation of H.261 sequence Figure 37 Bit rate for 1 GOP of MPEG sequence Figure 38 Effect of encoding parameters on bit rate Figure 41 Compexity measure for Graduation and Nursery In both sequences, the Standard Deviation is significantly reduced by the new method. The Table 5 Mean and Standard Deviation of PSNR Figure 42 PSNR of decoded sequences Figure 45 DC and 2 lowest AC coefficients a subset of the spatial frequencies. Figure 44 DC coefficients only Figure 47 All coefficients Figure 46 DC and lowest 9 AC coefficients Table 6 Decoded sequences Figure 50 Data rate of PSS JPEG The Baseline JPEG sequence with 10° bit errors showed very poor visual quality with Table 7 Quality of decoded video sequences many obvious “streaks” across the decoded frames (see the example in Figure 51). JPEG pixels as shown in this example. Figure 51 Baseline JPEG with bit errors resynchronization marker. This means that an error can often cause a “streak” of corrupted Figure 52 Mean PSNR of decoded sequences The mean PSNR for the two sequences (averaged across 5 experiments) is shown in Table Each macroblock consists of 16 x 16 luminance samples and so each slice in the 20_20_20 Table 11 Test sequences These slice sizes were chosen such that the file size (and hence the compression efficiency) Table 12 Varying slice sizes Sizes of 500-frame sequences (percentage of 20 20 20 sequence) Figure 53 Relative sizes of encoded sequences The re-animated 20_20_20 sequence showed a number of obvious, large disturbances Table 13 Improvement in PSNR due to varying slice size
