A Near-Lossless Image Compression Algorithm Suitable for Hardware Design in Wireless Endoscopy System
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Research Article A Near-Lossless Image Compression Algorithm Suitable for Hardware Design in Wireless Endoscopy System Xiang Xie, GuoLin Li, and ZhiHua Wang Department of Electronic Engineering, Tsinghua University, Beijing 100084, China Received 12 September 2005; Revised 28 February 2006; Accepted 7 April 2006 Recommended by Liang-Gee Chen In order to decrease the communication bandwidth and save the transmitting power in the wireless endoscopy capsule, this paper presents a new near-lossless image compression algorithm based on the Bayer format image suitable for hardware design. This algorithm can provide low average compression rate (2.12 bits/pixel) with high image quality (larger than 53.11 dB) for endoscopic images. Especially, it has low complexity hardware overhead (only two line buffers) and supports real-time compressing. In addition, the algorithm can provide lossless compression for the region of interest (ROI) and high-quality compression for other regions. The ROI can be selected arbitrarily by varying ROI parameters. In addition, the VLSI architecture of this compression algorithm is also given out. Its hardware design has been implemented in 0.18 µm CMOS process. Copyright © 2007 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Compared to the conventional endoscopy system, the wireless capsule endoscopy allows us to directly study the entire small intestine and does not require any sedation, anesthesia, or insufflation of the bowel. There is the only clinic device made by Israel in the world [1]. However, it can only work for less than eight hours (generally, it costs capsule about 10–48 h, typically 24 h, on moving from mouth to evacuation [1]) and the image frame rate is slow (2 frames/second), which results in the fact that there is not enough time for the capsule to check the large intestine, and some regions interesting to the doctors are often missed. By analyzing power consumption in capsule, it can be known that the power of transmitting image data occupies about 80% of the total power in capsule. In the digital wireless endoscopy capsule system designed by us, the power is supplied by two batteries and a CMOS image sensor is used [2]. In order to reduce the communication bandwidth and the transmitting power in the capsule, the image compression has to be applied. Although the CMOS sensors will bring some noises to the captured images, it does not affect the doctor’s diagnosis. Once the lossy compression is used, some information contained in the original images will be lost, which results in the error diagnosis. So a new low-complexity and high-quality image compression for digital image sensor with Bayer color filter arrays needs to be used [2]. Figure 1 shows the simplified
block diagram of our wireless endoscopy capsule system. The output image data from a CMOS image sensor is compressed first and then coded by channel coding module. Finally, the data are transmitted by a wireless transceiver to the outside of the body. The transmitted data will be received and dec
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