以JPEG-LS為基礎的感興趣區域編碼法實現膠囊內視鏡影像的無失真壓縮

摘要近年隨著數位科技的進步，醫學影像也大量被數位化，因而產生相當龐大的醫學影像資料。在遠距醫療(Telemedicine)的應用中，欲在有限頻寬的網路下傳輸如此龐大的資料，或是在歸檔儲存的應用中，在有限的儲存空間下要儲存如此龐大的資料都會造成很大的負擔，其中膠囊內視鏡就是一個典型的例子。而欲降低此負擔的一個解決之道就是資料壓縮。此外為了避免醫療糾紛，壓縮膠囊內視鏡影像最好使用無失真壓縮。因此針對膠囊內視鏡影像，本論文提出一個具有高壓縮效能的無失真壓縮方法。此壓縮法包含一特殊填補方式(padding scheme)且跟JPEG-LS相容，用於處理具有任意特定形狀及大小之感興趣區域(Region of Interest, ROI)的影像，例如應用在具有醫療診斷意義之感興趣區域的膠囊內視鏡影像上。本論文以JPEG-LS這項已被証明對於影像壓縮具有相當成效及低運算複雜度特性的壓縮標準為基礎，進行提升無失真膠囊內視鏡影像壓縮效能的研究。使用既有的JPEG-LS技術有不需要另外再發展一個全新壓縮演算法的優點，僅需針對影像具有ROI的特性及配合JPEG-LS的壓縮預測機制(prediction scheme)的需求，做好與原有技術的介面工作即可。實驗結果顯示，在壓縮效能方面，這套以感興趣區域為基礎的壓縮方法優於整張影像以JPEG-LS處理的方法。壓縮率上得到17％以上的增益(gain)，但在處理時間上卻節省了59％。在無失真壓縮的前提下能有如此優異的壓縮效能及執行速度更顯得可貴。此外，本論文所提出的壓縮方法，也適合其他具有ROI特性的醫學影像，例如乳房攝影及電腦斷層攝影等醫學影像。

關鍵字

邊緣填補；膠囊內視鏡影像；無失真壓縮； JPEG-LS、感興趣區域

並列摘要

Abstract As the development in digital technology continues to get progress rapidly, the digital data sizes of medical images increase quite enormously. In the application of telemedicine, transmission of such enormous amount of medical data becomes a heavy loading via a bandwidth-limited network. Similarly, in the archiving application, the requirement for saving such an enormous amount of data to limited storage space is a heavy burden too. Capsule endoscope is a typical source to create this kind of problem. One of the useful solutions to this problem is data compression. Furthermore, to aviod medical dispute, lossless compression is a better choice to compress capsule endoscope images than a lossy one. The thesis intends to propose a high-performance compression method that is particularly suitable for lossless compression of capsule endoscope images. In this thesis, a JPEG-LS-compatible compression algorithm based on a special padding scheme is presented to handle the images with arbitrary shapes and sizes of ROIs (region of interest) in a fixed template format. The proposed method is applied to the lossless compression of capsule endoscope images with diagnostic information contained in ROI zones. We use JPEG-LS which had already been proved with its excellen coding performance and low complexity feature in static image compression. With well-established JPEG-LS technology for image compression, it is needless to develop a whole new compression algorithm. All we need is to exploit the ROI characteristics of capsule endoscope images and be aware of the prediction requirement of JPEG-LS, and focus on the design of a good interface to the original technology. Experimental results show that this ROI-based method achieves better compression performance than a full-sized image based JPEG-LS method does. Specifically, the proposed method achieves 17% improvement in compression ratio, and saves the encoding time by about 59%. In the field of lossless compression, these results can be valuable and commendable. The proposed method in this thesis is also suitable for other ROI-based medical image compression applications, such as mammography, computed tomography, etc.

並列關鍵字

JPEG-LS ； border padding ； region of interest (ROI) ； capsule endoscope image ； lossless compression

參考文獻

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以JPEG-LS為基礎的感興趣區域編碼法實現膠囊內視鏡影像的無失真壓縮

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