用於影像壓縮之方向性多重解析度轉換和區塊位元平面算數編碼

Abstract

連續畫面小波視訊轉換(Interframe Wavelet Video Coding)擁有訊雜比可調性、時間軸上可調性和畫面解析度可調性的好處，小波轉換在此編碼架構中扮演重要角色，另外算數編碼器在整體編碼中也是一個不可忽略的要件，因為算數編碼器產生影像壓縮的最後位元串流。 我們實驗平台的來源是MPEG可調式影像編碼核心實驗參考軟體，藉著修改參考軟體架構來實現本論文的想法。 在本論文共包含兩個研究主題，其中一個主題針對是加化熵編碼效率的方法，並在實驗中將這方法整合到連續畫面小波視訊轉換的架構中。主要原理是根據能量聚集來提昇編碼效率，實驗的結果可以看到編碼位元數量的減少，然而要使這方法有更高效率是需要更深入的研究。 另外一個研究是將原本連續畫面小波視訊轉換架構的空間轉換替代成方向性多重解析轉換。方向性多重解析轉換主要是以Minh N. Do提出的階層式方向性濾波組為基礎，將圖片分解成不同解析度和方向性的成分。在最後的模擬結果可以看到在高壓縮比率下訊雜比和視覺品質會較原方法提升。

Interframe wavelet coding has the advantage of SNR, temporal, and spatial scalability. Wavelet Transform Coding is one of the most essential components in the interframe wavelet coding architecture. The arithmetic entropy subsystem is another indispensable element in Wavelet Transform Coding. It produces the final compressed output bit stream. This thesis contains two major topics. One is an enhanced entropy coding scheme that can be incorporated into the interframe wavelet coding architecture. Another topic is replacing the original separable wavelet by the directional multiresolution transform. We modify the entropy coding syntax/scheme originally used in the MPEG SVC Core Experiment (CE) reference software. We take the advantage of energy clustering properly to improve coding efficiency. We have observed some bit savings of this technique in our simulations under the conditions specified by the MPEG core experiments; however, the full potential of this technique is yet to be further explored. The directional multiresolution transform decomposes an image into different resolution and direction components. It seems to be a more compact and efficient representation of images. We use the directional filter back to replace the separable wavelet in the MPEG wavelet software. The improvement of PSNR and visual quality can be observed on the low bitrate compressed images.