利用統計方法比較壓縮醫學影像品質

Comparing JPEG with Wavelet Compression by Using Statistical Method

蕭雅慧(Ya-Hui Shiao) ； 莊克士(Keh-Shih Chung) ； 陳宗哲(Tzong-Jer Chen)

《中華放射線技術學雜誌》 31卷1期 (2007/06) Pp. 1-13

https://doi.org/10.30045/CJRT.200706.0001

摘要

隨著數位影像廣泛應用，有損壓縮(lossy compression)因具較高之壓縮能力，將逐漸成為壓縮方法的主流，但其可能造成重要資訊損失，故有損壓縮在醫學影像上僅適合低倍壓縮，而欲如何提高壓縮比又不影響影像品質，是大家追求的目標。小波壓縮(wavelet compression)與JPEG (Joint Photographic Experts Group)壓縮，是目前較常使用的醫學影像壓縮法，一般顯示在高壓縮比下小波壓縮較JPEG壓縮好。影像品質評估在影像處理上一直扮演著重要角色，ROC (Receiver Operating Characteristic)是種著名評估影像品質的方法，但若欲利用此法探究低壓縮比(約小於25倍)的影像品質時，因其變化甚少，難以肉眼評估，使得JPEG與小波壓縮哪種方法好，至今尚未有一定論。因此本研究主要是利用客觀的統計方法，比較小波與JPEG兩種壓縮影像品質。文中採用CR、CT以及MRI之T1等三種醫學影像，並使用Moran's I測試，發展影像品質評估指標，作為小波與JPEG壓縮在三種醫學影像低壓縮比時，影像品質評估之較客觀依據。結果顯示約10倍壓縮比以下，JPEG壓縮較小波壓縮好；而壓縮比在10至25倍時，則呈現小波壓縮較JPEG壓縮好。未來希望能將這些統計方法應用在更多影像品質評估上。

關鍵字

有損壓縮 ； 小波壓縮 ； JPEG壓縮 ； Moran's I測試 ； 統計方法

並列摘要

With the widely applications of digital images, the lossy compression will gradually become the mainstream of compression methods. Because this method might cause the lost of important information, only compression with low ratio are considered on medical images. The goal that we are pursuing is to maximize compression ratio while keeping image quality unchanged. Therefore image quality assessment plays an important role for it. ROC (Receiver Operating Characteristic) is a well-known method for evaluating wavelet compression and JPEG (Joint Photographic Experts Group) compression. Human eyes are difficult to differentiate the nuances of compressed images at low compression ratio. Our research focuses on evaluating image quality by using statistic methods. We develop some image quality indexes using Moran's I test to evaluate the image quality of wavelet and JPEG compression at low compression ratio (about ＜ 25 times). The results indicate that JPEG compression is better than wavelet compression when the ratio is below 10 times and the reverse is true at compression ratio from 10 to 25 times.

並列關鍵字

lossy compression ； wavelet compression ； JPEG compression ； Moran's I test ； statistic method