Robust MPEG-2 SNR Scalable Coding Using Variable End-of-Block Rogelio Hasimoto-Beltrán Ashfaq A. Khokhar Center for Research in Mathematics (CIMAT) University of Illinois at Chicago Guanajuato, Gto. México 36240 Chicago, IL 60605 hasimoto@cimat.mx ashfaq@uic.edu Abstract Signal-to-Noise Ratio (SNR) scalable coding over priority networks has been used as a robust mechanism to transmission errors, since the most important information (base layer) can be sent over an error free channel as in the case of ATM networks or over protected channel as in the case of IP networks. SNR scalability ensures a minimum video quality at the receiver end by sacrificing the least important information (enhancement layer) when losses occur. However, one disadvantage of scalable coding is its lower compression performance with respect to the one-layer encoding (~10-15%, [1]). In this work, we propose an error resilient scheme for MPEG-2 SNR scalable video transmission that is compression efficient, in addition to providing scalable error resynchronization mechanism to enhancement layer that impedes the propagation of errors beyond the physically affected area in the bitstream. In order to provide robustness to errors during transmission, the proposed scheme uses triangular coding in the transform domain [2] and a modified variable end of block based on the number of bits per unit of block. Our scheme yields significantly better compression ratios compared to the MPEG-2 standard (3% to 6.7%) while at the same time improves considerably the quality of the received data (2-11 db) under different conditions of data losses. 1. Introduction An important characteristic of multimedia content communication (in particular image/video communication) is that it requires quality of service in terms of low latency, better PSNR, and low jitter, under the pretext of high bandwidth bursty traffic, that is, too much information is being generated in a small period of time. For the Internet, which is based on besteffort datagram delivery, no bandwidth is reserved for specific connections. The capacity may be exceeded and queues within the network may grow until eventually they are full. Under such a scenario, the network starts dropping packets. Once a packet has been lost (because of the buffer overflow), it is likely that the next packet will also be lost, especially if the inter-arrival time is less than the service time [3]. Therefore, packet losses are correlated and might occur in bursts. Similar behavior of packet losses is also seen in ATM networks [4]. Another important factor to be considered in compressed image/video transmission is that packet losses and/or bit errors can easily propagate to contiguous areas due to the loss synchronization (sync) in the bitstream. When sync is lost and not detected, the decoder may be wrongly decoding the bitstream (it does not stop the decoding process), conversely when a sync error is detected the decoder stops decoding and discards the rest of the bitstream up to a sequence marker or start code in order to regain synchronization. Data lost along with error propagation (due to a loss in sync) severely degrade the visual quality of the transmitted information. Several methods have been proposed in the literature in order to prevent a drastic degradation in the video quality due to transmission errors; among them is Layered or Scalable Coding. There are different modes of scalability; the one we are interested in is SNR scalability in the MPEG-2 standard. SNR scalable video coding generates two layers of equal spatial resolution but at different qualities: the Base Layer (BL) and the Enhancement Layer (EL) [5]. The base layer contains header information and a coarse version of the DCT coefficients, while the enhancement layer is the refinement step of the base layer. At the encoder, each output layer is independently entropy encoded and transmitted over its corresponding priority channel. High priority level (better error performance) can be given to the base layer for providing the most important contribution to the decoded quality, and low priority to the enhancement layers. In ATM networks, priority levels
are used by the network protocol to decide which layer has to be dropped out in the case of congestion (thus maintaining the most important information on its way to the receiver). One of the drawbacks of scalable coding is its relative lower compression performance with respect to the one-layered encoding due to an extra overhead in the enhancement layer at both the Macroblock (MB) header level and data level. We are particularly interested in the overhead produced by the End-of-Block (EOB) at the data level, which for an n layer scalability represents n*(number_of_blocks*eob) bits, where EOB = 4 bits for Intra-frames. Our purpose in this work is to reduce the effect of scalable coding on the final compression ratio and at the same time provide protection to the enhancement layer against error propagation in the bitstream. To increase the performance compression of the SNR scalable coding, we propose the use a variable end-of-block technique based on the number of AC coefficients per block (VAC-EOB) on the base layer. This scheme has been proved to be effective on JPEG images for medium to high compression ratio, which is the case of base layers in scalable coding. VAC-EOB can also be combined with Triangular Coding (TC) in order to increase the compression ratio and resilience against bursty network errors [2]. To protect the enhancement layer against error propagation, we propose a variable end-of-block based on the number of bits per unit of block (VB-EOB), which prevents the error propagation beyond a pre-selected unit of block (block, ½ MB, MB, etc.). The problem of error propagation due to a loss in synchronization has been addressed in video coders (MPEG-X and H.26X) by introducing Synchronization Markers (SM) in the bitstream [6, 7] and Fixed-Length Code words (FLC) [8]. The former involves the addition of redundant information (~24 bits plus an 8- bit vertical position information in MPEG-2) placed at some points in the image/video layer structure, while the latter requires additional complexity over the standard schemes and often results in lower compression efficiency [9]. A more sophisticated method that has been proposed to alleviate the synchronization problem is Reversible Variable- Length Code (RVLC) along with SM [10]. The advantage of RVLC over standard VLCs is that the bit stream can be decoded in the backward direction as well. Another alternative scheme called Error Resilient Entropy Code (EREC) has been proposed in [9], which protects encoded data against synchronization errors at a block level (that is in the case of errors the decoder can find the start of the next block). In addition to providing good resilience to channel errors, it has the advantage that compression ratio is unaffected. In this work, we propose fast error synchronization based on the number of bits per unit of block, which different Video Input DCT Q Low than previous schemes is scalable in terms of providing protection according to the network error conditions during transmission. Our scheme is compression dependent, and it works better (in terms of gain in CR) for high to medium compression rates (low to good/very good picture quality). The rest of the paper is organized as follows. In Section 2, we describe the error resilient scheme, which is a combination of triangular coding and a scalable error propagation protection using VB-EOB. In section 3 we show the effect of the proposed scheme on compression and under network errors. Conclusions and future work are presented in Section 4. 2. Proposed Scheme We briefly describe the fundaments of MPEG-2 SNR scalable video coding and then explain our proposed scheme based on variable end-of block. 2.1 SNR Scalable Coding Q Hig -1 Q Low VLC VLC Lower Layer Bitstream Enhancement Layer Bitstream Figure 1. SNR scalable encoder by quantizer refinement. Figure 1, shows an SNR scalable encoder by quantizer refinement for Intra-frames. The encoder outputs two-layer pictures, the lower layer and the enhancement layer. Most of the header information (Picture header, MB type, motion vectors, etc) is contained in the lower layer; the enhancement layer is practically reduced to DCT refinement coefficients only. The lower layer follows the one-layer MPEG-2 encoding process, in which the intra-frame is divided into slices, slices into Macroblocks (MB), and MB into blocks of 8x8 pixels. Every block is then transformed to the frequency domain using the Discrete Cosine Transform (DCT) and quantized using a rather coarse quantization matrix (Q LOW ) producing a low quality picture. The enhancement layer is a quantized version (using Q High ) of the quantization error in the lower layer. Both layers are independently variable length encoded. During this step (Variable Length Coding-- VLC) process, a 4-bit end-of-block (EOB) is allocated
for each block (specifying the boundaries among adjacent blocks), and a 32-bit slice start code is allocated at the end of each slice. The slice start code is important in the handling of errors. The decoder can skip the corrupted slice and go to the start of the next slice if the bitstream is corrupted by noise [5]. Depending on the network error condition, the number of slices can be increased up to the number of MBs in the intra-frame, obviously affecting the CR of the encoder. An n-layer scalable coder will produce an overhead of (n*number_of_blocks*4 + n*number_of_slices*32) bits related to the EOB (4 bits) and slice start code (32 bits) respectively. In order to improve the compression ratio and error resilience of scalable coding, we propose to replace the EOB and slice start code of the enhancement layers by a variable end-of-block based on the number of bits per unit of block and use a Variable end-of-block based on the number of AC coefficients (VAC-EOB) on the lower layer. In particular VAC-EOB has been applied at a block and triangular block basis on JPEG images, producing a gain in CR for medium to high CRs, which is the case for the lower layer. We describe in the next section the VAC-EOB and triangular coding (TC), which are the basis of our proposed scheme. The base and enhancement layers are separately decoded and inverse quantized. After this, their respective DCT coefficients are added together. If the enhancement layer is lost during transmission, the base layer can be decoded independently, but the final quality will be lower than the original encoded video; on the other hand if the base layer is lost, the decoder cannot decode the enhancement layer independently. 2.2 Variable End-of-Block In the MPEG-2 Intra-frame, a fixed size 4-bit EOB marker is placed at the end of each block regardless of the number of bits inside the block. This contributes a significant overhead in the overall compressed bit stream and it gets worse for scalable encoding. We have observed that the number of AC coefficients per block is relatively small and pretty repetitive. For example, in the case of Lenna at 0.5 bpp, there are 20 different AC frequencies (with an average of 3.5 coefficients per bock), where 40% of the blocks contain zero or one AC coefficients and 60% of the blocks contain between two and 19 coefficients. Based on this information, we can encode the number of AC coefficients in each block using the Huffman code and use this code as the EOB marker. We refer to this EOB as VAC-EOB. As an average, VAC-EOB gives better performance than the constant 4-bit EOB [2]. Another interesting result obtained in [2] for JPEG images, is that of combining VAC-EOB and TC. This combination improves compression and error resilience 1 15 17 31 2 16 18 32 3 13 19 29 Original Image 4 14 20 30 5 11 21 27 6 12 22 28 7 9 23 25 Lower Triangle (L) dc 8 10 24 26 Triangular Interleaving 4 8 12 16 1 5 9 13 32 28 24 20 29 25 21 17 2 6 10 14 31 3 7 11 30 26 22 18 27 23 19 15 Interleaved Image AC's DCT Block (8x8) Upper Triangle (U) Figure 2: Triangular-based Interleaving (TRII) scheme. against correlated losses (bursty packet/cell losses) by decomposing an 8 x 8 block of DCT coefficients into three frequency components, DC term, lower triangle (L), and upper triangle (U), as shown in Figure 2. DC is encoded independently to L and U. L and U can be either encoded independently to each other or they can be merged together to create a new block, which is then encoded following the MPEG-2. One of the advantages of this scheme is that each triangular region (U or L) can be sent far apart from each other (decorrelation process or data interleaving) in order to avoid correlated losses of information, in this way only one half-block (U or L) might be damaged. Figure 2 shows an interleaving scheme in which the L component of block 1 has been merged with the U component of block 2 and so forth to form Layer 1. Next, the U component in block 1 has been merged with the L component of block 2 and so forth to form Layer 2. Layer 1 is sent first followed by Layer 2. Under this scheme, if a block is damaged or lost, it can be reconstructed from its neighborhood. Let s assume that block with L=13 and U=16 is lost during transmission, then the L component can be recovered from the surrounding blocks having the L = {1, 3, 5, 11, 21, 19 and 17}, and U=16 can be reconstructed from surrounding blocks having the U = {2, 4, 6, 12, 22, 20, 18 and 16}. When L and U are coded independently, an additional VAC-EOB is needed per block; despite of this the CR improves considerably. 2.3 Robust MPEG-2 Coding through VB-EOB Once the correspondent bitstreams of the base and enhancement layers are generated, a service contract is established specifying their QoS. The base layer is sent over a high priority channel (error free channel) and the enhancement layer using the Available Bit Rate Layer1 Layer2
MB 1 MB 2 1 2 5 6 3 4 7 8 1 2 3 4 5 6 7 8 VB-EOB 1 VB-EOB 2 VB-EOB 1 VB-EOB 2 = VAC-EOB Figure 3: Scalable VB-EOB protection at MB level. Gray rectangles at the beginning of a block represent a VAC-EOB. VB-EOB i is the variable end of block using the number of pixels in the MB, including VAC-EOBs. (ABR) service. ABR is a lossy service that uses the leftover capacity from the Constant Bit Rate (CBR) and Variable Bit Rate (VBR) services. As in the case of CBR and VBR services, ABR negotiates the Minimum Cell Rate (MCR) of transmission at the beginning of the session. If transmitting beyond the MCR limit, errors may appear depending on the network traffic [11]. As we see, the EL is the one that has to be protected against transmission errors. In order to protect the enhancement layer against synchronization errors (errors spreading beyond the physically affected area) produced by a cell loss or a simple bit error, we have developed a scalable protection using a variable end of block based on the number of encoded bits per block, ½-MB, MB, 2-MB, or 4-MB (instead of the number of AC coefficients as in the case of VAC-EOB). The protection level depends on the network error condition; high error rates require good protection of the bitstream, for example block level protection. In block protection the number of bits per block will be known at the receiver, so in the case of error propagation the resynchronization process can be acquired at the next block instead of the beginning of the next slice. This avoids discarding a considerable amount of information in the bitstream, improving the quality of the received video frame. Figure 3, depicts the scheme of error propagation protection at a MB level (every 4 blocks). The EOB in blocks 1-3 are of the form VAC- EOB and the VB-EOB i is computed over all bits in the MB including the VAC-EOBs. Note that for inner blocks the variable end of block is moved at the beginning of the each block, in order to simplify the decoding process. The process described above is performed only for intra frames. A small overhead specified in the enhancement layer can be omitted if we use a constant quantizer_scale_code, therefore no Macro-block type table is needed either. No coded_block_pattern is considered for intra frames in the MPEG-2 standard. With this constrained, the position (start and end) of each protection level (block, half MB, MB, etc.) in the resulting bit stream is now known (since we are sending only refinement DC coefficients in the enhancement layer). In the case of a cell loss or a bit error, only the damaged encoded level is skipped, and the decoding process can be restarted at the beginning of the next level (not at the beginning of the next sequence marker as in MPEG-2). This scheme is effective under both random and burst cell losses and bit errors, because the resynchronization process is independent of the number of errors in the bit stream. 3 Experimental Results Let us first analyze the compression performance of VAC-EOB applied to both base and enhancement layers. CIF frames (frame 1) from Akiyo and Flower- Garden (FG) sequences at different compression ratios were used in the analysis. The images were processed as follows. Once a compression level for the base layer is fixed, the quantization level of the enhancement layer is varied (according to bpp_range) in order to provide good to very good subjective image quality, and the average compression gain over all quantization levels is calculated (see Table 1). In computing the average compression gain, we used the best result between VAC-EOB and VAC-EOB with Independent Triangular Coding (V-ITC) in both layers (represented as V-EOB in Table 1). We also varied the base layer quality (rows in Table 1) from low (highest compression level allowed by MPEG-2) to good subjective image quality, approximately 0.55 bpp for Akiyo and 0.80 bpp for Flower-Garden. The performance of variable end of block (VAC-EOB or V-ITC) is better at high compression ratios. The average gain in compression ratio over the MPEG-2 standard fluctuates between 3.6%-6.7% for Akiyo (Table 1a) and 3.0%-3.5% for Flower-Garden (Table 1b). The highest values were obtained by setting the base layer at the highest compression level allowed by MPEG-2 and varying the end image quality (base + enhancement layer) from good to very good (represented by bpp range in Table 1). In general, the compression gain in the case of FG video is relatively lower than Akiyo; this is because FG does not yield high compression due to its high frequency content. The use of VAC-EOB or V-ITC improves compression, but it is not robust to synchronization errors. For this, we apply a scalable bit-protection
Bpp Table 1a. Average compression gain for VAC-EOB with respect to the SNR scalable MPEG-2 standard. Simulation was run for frame 1 of Akiyo. Base Layer (BL) AC + DC (bits) V-EOB Gain (%) Enhancement Layer (EL) Avg. AC V-EOB coeff. Avg Gain (bits) (%) bpp range (min-max) SNR Performance Avg. bpp Increment wrt to BL Avg. CR Gain (%) 0.2616 3625 14.7 46623 3.0 (0.58,1.00) 0.5219 6.7 0.3089 8412 9.6 37524 3.7 (0.56,1.00) 0.4298 6.0 0.4062 18281 5.6 21584 3.1 (0.61,1.01) 0.3700 4.1 0.5073 28532 4.3 28470 3.6 (0.70,1.02) 0.3400 3.6 bpp Table 1b. Same as Table 1a except that simulation was run for frame 1 of FG. Base Layer (BL) AC + DC (bits) V-EOB Gain (%) Enhancement Layer (EL) Avg. AC V-EOB coeff. Avg Gain (bits) (%) bpp-range (min-max) SNR Performance Avg. bpp Increment wrt to BL Avg. CR Gain (%) 0.4977 25259 4.0 38461 3.5 (0.76-1.11) 0.4406 3.3 0.5922 34737 3.2 34720 4.7 (0.84-1.13) 0.4038 3.1 0.7089 46568 1.7 28270 11.0 (0.98-1.20) 0.3436 3.5 0.8087 56685 1.3 29461 10.5 (1.03-1.28) 0.3520 3.0 Table 2a. Average CR gain and bpp increment at block, 2-MB and 4-MB protection levels. Bpp increment represents the average increment in quality provided by the enhancement layer for a fixed base layer quality. Simulation was run for frame 1 of Akiyo. Base Layer (BL) (Avg. CR gain [%], Avg. bpp increment wrt to BL) bpp Block 2-MB 4-MB 0.2616 (1.8, 0.30) (1.8, 0.33) (3.8, 0.43) 0.3089 (2.4, 0.25) (1.5, 0.27) (2.9, 0.30) 0.4062 (1.3, 0.26) (1.7, 0.26) (2.6, 0.27) 0.5073 (1.6, 0.27) (1.5, 0.22) (2.3, 0.24) Total (Gain/increment) (1.7, 0.27) (1.6, 0.27) (2.9, 0.31) Table 2b. Same as Table 2a except that simulation was run for frame 1 of FG. Base Layer (B (Avg. CR gain [%], Avg. bpp increment wrt to BL) bpp Block 2-MB 4-MB 0.4977 (1.5, 0.24) (1.7, 0.24) (2.5, 0.27) 0.5922 (0.8, 0.29) (0.8, 0.25) (1.6, 0.29) 0.7089 (1.0, 0.21) (1.2, 0.21) (1.6, 0.24) 0.8087 (0.4, 0.23) (0.5, 0.23) (1.1, 0.27) Total Gain (0.9, 0.24) (1.1, 0.23) (1.7, 0.27)
as shown in Figure 3. The base layer is left unmodified as in the previous analysis and the enhancement layer receives scalable protection at any of the following levels: block, ½-MB, 1-MB, 2-MB, and 4-MB level. Tables 2a and 2b show that the protection level is proportional to the level of compression; at higher compression ratios protection may reach its highest point (block level). As compression ratio decreases, so does the protection level to 4-MB; this is to avoid penalties in the compression performance. Table 2 does not show the performance of ½-MB, MB, and 2-MB because there was a small performance difference with respect to the block level protection (in some cases, the performance was a little lower). This problem is related to an increase in size of the V-ITC Huffman table, which reduced the gain between half MB to 2-MB protection levels, and increased again for 2-MB and 4- MB. In our scheme, the enhancement layer is naturally byte aligned according to a specified level of protection (block, ½-MB,, or 4-MB), therefore the use of the start codes are not useful anymore. If we consider start codes at the end of each row (MPEG-2 allows a variable slice size), we have an additional gain of 576, 1408, and 2816 bits for CIF, 4CIF and 16CIF intra frames, respectively. How significant is the gain in every protection level?. In general, the enhancement layer refinement with scalable protection can increase the quality of the base layer as much as 0.31 bpp as an average for Akiyo and 0.27 for FG and still have gain with respect to the SNR scalable profile. In order to have the highest protection level (block protection), the increase in bpp of the refinement layer must not exceed as an average 0.27 bpp and 0.24 bpp for Akiyo and FG respectively. In protecting the enhancement layer against propagation errors due to a sync loss in the bitstream, we are creating additional information such as Huffman tables and end of blocks codes VAC-EOB and VB- EOB, which are very sensitive to network errors. The most important information in considering transmission errors and its effect in the decoded image quality is the one provided by the Huffman tables and the variable EOB code stream based on the number of bits per protection level. We want this information to reach the receiver end error free. There are several ways to do this, the easiest one would be to include this information as part of the base layer and send it over the error free channel, causing an increase in the base layer data of 2%-15% (but at the same way causing a decrease in the enhancement layer data by the same magnitude). A second solution and most plausible one is to negotiate the MCR such that at least (under heavy traffic condition) we can transmit the Huffman tables and the EOB code error free (we analyze this solution later in this section). These two solutions keep the compression gain obtained in our proposed scheme unchangeable. Let s assume for the moment that the network cannot provide any QoS to the enhancement layer (pretty much like an IP network) and we need to provide that protection using Forward Error Correction (FEC). The question we made above can be answer as follow: how much FEC protection can be provided to the most important data (VB-EOB data and its corresponding Huffman table) at different protection levels?. With a protection level of 4-MB, we can use FEC to protect 77% of the most important information in the average for Akiyo, and 64% for Flower-Garden. The minimum FEC protection is at the block level with 15% and 13% for Akiyo and FG respectively. FEC protection can be used as last resource, only in the case where MCR cannot provide error free transmission for the most important data at a given protection level. 3.1 Performance of VB-EOB under Network Errors We simulated the scalable transmission of Akiyo and Flower-Garden over ATM, under 1% 5% 10% 15%, 20% and 25% cell loss rate (CLR) on the enhancement layer. Five simulations were performed and averaged at each error percentage. Different scalable protection levels were applied; block and 4- MB for Akiyo and only 4-MB for FG and compared against the MPEG-2 standard with start code at every slice and at every 4 slices (4-slice). A quantizer scale code of 31 for the base layer and 13 for the enhancement layer were used for Akiyo to get a combined scalable quality of 0.6369 bpp. For FG we use a quantizer scale code of 29 for the base layer and 25 for the enhancement layer for a combined scalable quality of 0.8262 bpp. For Akiyo (Figure 4), VB-EOB produced an average improvement of 3.6 db and 6.4 db with respect to MPEG-2 with start code at slice and 4-slice respectively. With 4-MB protection, the average gain is 3.1 db and 5.3 db over the MPEG-2 standard with start code at slice and 4-slice respectively. With block protection for a constant 37 db output PSNR, our scheme withstand 3.5 times as many lost cells than the MPEG-2 with start code at every slice and 8 times when the start code is set to every 4 slices. For FG (Figure 5) at 4-MB protection level an average improvement of 3.1 db and 6.4 db with respect to MPEG-2 with start code at slice and 4-slice respectively were obtained (this is close to the values obtained for Akiyo at block level protection). At a constant 41 db output PSNR, our scheme withstands 2.5 times as many lost cells as in MPEG-2 with start code at every slice and 8.3 times when the start code is set to every 4 slices.
Redmill and Kingsbury [9] presented an Error Resilient Entropy Code (EREC) for block desynchronization that reorganizes the variable-length code such that each block starts at a known position within the code. Under channel error conditions, the decoder can find the start of each block automatically. The goal of EREC and our scheme is the same, i.e., stop de-synchronization as quicly as possible. However, EREC does it at one level only (block level), whereas our proposed VB-EOB can be applied at multiple levels (depending on the degree of bit errors in the channel), such as ½-Macroblocks, Macroblocks, 2- Macroblocks, 4-Macroblocks, Slice, etc. EREC is independent of the compression ratio and requires a minimal data overhead; VB-EOB is effective under high CRs in non-scalable coding and under medium to high CRs if SNR scalability is used. EREC implies significant memory requirements and delay [9], while VB-EOB is simple and only requires the computation of at the most two Huffman tables with average size of 70 elements. 4. Conclusions and Future Work We have presented a new compression efficient scheme for SNR scalable MPEG-2 transmission that provides protection to the enhancement layer against synchronization errors up to a block level. The scheme is based on variable end of block based on the number of bits per unit of block (VB-EOB). We have presented experimental results for different images and network scenarios. We have shown compression ratio gains up to 6% higher than the MPEG-2 SNR scalable profile. Our proposed protection is scalable to block, ½-MB, 1- MB, 2-MB and 4-MB levels, with the highest protection provided at block level. Under 1%-25% CLR, the scalable protection provided better PSNR than MPEG-2, going from 2.2-5.5 db when using block level protection and MPEG-2 slice start codes, and from 4.2-10.8 db when using block level protection and start codes every 4 slices in MPEG-2. One of the main drawbacks in our scalable error protection scheme is the creation and transmission Huffman tables and end of block codes, which end up reducing the performance of the scheme in addition to be very sensitive to network errors. One solution for a future work is the creation of static Huffman tables, which can be known by both the encoder and decoder. In this way, we increase the applicability of the scalable error protection to lower compression ratios in scalable and non-scalable coding. Acknowledgement This work was supported by CONCYTEG under grant number 04-02-K117-020. PSNR (db) 55 50 45 40 35 30 Figure 4: Degradation of signal to noise ratio vs. channel cell loss rate (CLR) for frame 1 of Akiyo. PSNR (db) 60 55 50 45 40 35 30 References Akiyo MPEG-2 (4-Slice) MPEG-2 (Slice) Block 4-MB 1 52 10 3 15 4 20 5 25 6 CLR (%) Flower-Garden MPEG-2 (4-Slice) MPEG-2 (Slice) 4-MB 1 5 2 10 3 15 4 20 5 25 6 CLR (%) Figure 5: Degradation of signal to noise ratio vs. channel cell loss rate (CLR) for frame 1 of Flower Garden. [1] D. Wilson and M. Ghanbari, Optimization of MPEG-2 Scalable Codecs. IEEE Trans. On Image Processing,, Vol. 8, No. 8, October 1999. [2] R. Hasimoto-Beltran, S. A. Sheikh, and A. Khokhar, A Compression-Efficient Forward Error Control for Image Transmision over ATM Networks. ICME 2000, New York, NY, July-August 2000. [3] J. C. Bolot, Characterizing End-to-End Delay and Loss in the Internet. Journal of High Speed Networks, Vol.2, No.3, pp. 305-323, December 1993. [4] X. Lee, Y-Q. Zhang, and A. Leon-Garcia, Information Loss Recovery for Block-based Image Coding Techniques: A Fuzzy Logic Approach. IEEE Trans. Image Processing, Vol. 4, No. 3, pp 259-273, March 1995. [5] Rao K. R. and J. J. Wang, Techniques & Standards for Image/Video & Audio Coding. Prentice Hall, Inc., 1996.
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