Pre-processing images prior to encoding can remove noise, or unimportant detail, and thus improve the overall performance of the coder. Typical objective image quality metrics are obtained by computing a single or sev...
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ISBN:
(纸本)0819425869
Pre-processing images prior to encoding can remove noise, or unimportant detail, and thus improve the overall performance of the coder. Typical objective image quality metrics are obtained by computing a single or several numbers as a function of the difference image between the original and coded images. Such metrics may not reflect the improvement in performance. In a recent paper we have presented a methodology that allows the quantitative determination of image quality when the image has been processed prior to encoding. We now present an extension of the work showing global objective quality measures that quantify the value of pre-processing for image coding using a wavelet coder. Because many options are available in wavelet coder design, we limit our study to a ''best'' coder obtained in previous work, and determine what further performance improvement can be achieved by image processing.
Video-object coding is one of the most important functionalities proposed by MPEG-4. In this paper, we propose a new wavelet method to encode the texture of an arbitrarily shaped object, both for the still and for the...
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Video-object coding is one of the most important functionalities proposed by MPEG-4. In this paper, we propose a new wavelet method to encode the texture of an arbitrarily shaped object, both for the still and for the video object. The method uses the shape adaptive wavelet transform (SA-DWT) in MPEG-4 still object coding, but with a computationally more efficient lifting implementation. The transformed object coefficients are then quantized and entropy encoded with a partial bit-plane embedded coder, which greatly improves the coding efficiency. We denote the coding algorithm as the video object wavelet (VOW) coder. Experimental results show that VOW significantly outperforms MPEG-4 in still-object coding, and achieves a comparable performance in video object coding in terms of PSNR. Moreover, the VOW decoded object looks better subjectively, with less annoying blocking artifacts than that of MPEG-4.
We present two methods for protecting a region of interest (ROI) in a compressed medical image transmitted across a lossy packet network such as the Internet or a wireless channel. We begin with a high quality wavelet...
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ISBN:
(纸本)0819444308
We present two methods for protecting a region of interest (ROI) in a compressed medical image transmitted across a lossy packet network such as the Internet or a wireless channel. We begin with a high quality wavelet-based coder, the Set Partitioning in Hierarchical Trees (SPIHT) algorithm, which orders data progressively by coding the globally important information first. We then compress the ROI to a higher quality than the rest of the image by scaling the wavelet coefficients corresponding to the ROI. This approach moves ROI information earlier in the bit stream. Finally, we add more redundancy to the ROI than to the rest of the image by two techniques. With MD-SPIHT, we repeat wavelet coefficient trees corresponding to the ROI and code them to higher bit rates than the background trees. With ULP-FEC, we use forward error correction (FEC) in an unequal loss protection framework. We find that both methods increase the probability of receiving high quality ROI in the presence of packet loss.
A new embedded wavelet coder called the multithreshold wavelet coder (MTWC) was proposed in this research. The new coder was motivated by a careful analysis of the rate-distortion performance and the coding efficiency...
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ISBN:
(纸本)0819425869
A new embedded wavelet coder called the multithreshold wavelet coder (MTWC) was proposed in this research. The new coder was motivated by a careful analysis of the rate-distortion performance and the coding efficiency of existing embedded wavelet coders. Unlike other proposed embedded wavelet coders which use a single initial threshold in their successive approximate quantization (SAQ), MTWC uses different initial thresholds in different subbands and applies a subband decision scheme to decide which subband should be coded in sequence. It is shown with experimental results that MTWC has a better rate-distortion tradeoff at higher bit rates and a lower computational complexity than other embedded wavelet coders. Furthermore, MTWC can be easily applied to an image coder with the wavelet packet transform, whose performance is significantly better than the image coder with the pyramid wavelet transform for texture-dominant imagery.
The volume of medical image data is expected to increase dramatically in the next decade due to the large use of radiological image for medical diagnosis. The economics of distributing the medical image dictate that d...
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ISBN:
(纸本)0819429155
The volume of medical image data is expected to increase dramatically in the next decade due to the large use of radiological image for medical diagnosis. The economics of distributing the medical image dictate that data compression is essential. While there is lossy image compression, the medical image must be recorded and transmitted lossless before it reaches the users to avoid wrong diagnosis due to the image data lost. Therefore, a low complexity, high performance lossless compression schematic that can approach the theoretic bound and operate in near real-time is needed. In this paper, we propose a hybrid image coder to compress the digitized medical image without any data loss. The hybrid coder is constituted of two key components: an embedded wavelet coder and a lossless run-length coder. In this system, the medical image is compressed with the lossy wavelet coder first, and the residual image between the original and the compressed ones is further compressed with the run-length coder. Several optimization schemes have been used in these coders to increase the coding performance. It is shown that the proposed algorithm is with higher compression ratio than run-length entropy coders such as arithmetic, Kuffman and Lempel-Ziv coders.
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