臺灣博碩士論文加值系統

JPEG2000不僅在壓縮效能上勝過JPEG，尤其對影像傳輸需具備Embedded & Progressive及對抗錯的要求下，更是有優越的表現。相較於JPEG的DCT量化之正規矩陣已有融入人類視覺特性，但是JPEG2000的缺點是目前為止尚未利用人類視覺特性，因此論文提出一種新的影像壓縮演算法，稱之為JND_JPEG2000。融入1998年Shen and Yuan 提出之JND視覺模型，發展於JPEG2000前處理與後處理程序。經由實驗證明，SY_JND_SQ能根據視覺特性，有效分配係數總數量減少編碼之位元數，達到視覺無失真的效果且反應出視覺的重要性並降低計算量的功效。根據一種視覺無失真檢驗的"VLLCVD"，為基礎發展出一套較嚴謹的主觀影像品質評估準則， 證實同樣位元率之下SY_JND_JPEG2000視覺品質優於一般JPEG2000與WYSV_JND_JPEG2000結果。本文也提出視覺權重客觀評估之JND_PSNR並與主觀之無失真切換檢驗法作驗證，證明JND_PSNR可取代耗時耗力之主觀測試。採用本文之SY_JND_JPEG2000在同樣位元率時，不僅提供較佳的視覺品質且計算量大幅降低，以高位元率Lena為例約節省50％計算量。

Recently, the wavelet based JPEG2000 algorithm has attracted significant attentions from researchers in image coding. JPEG2000 maximizes the PSNR value (or minimize MSE value) for each transmitted bit. However, it is well known that PSNR is not a good indicator for the perceptual image fidelity. Human visual perception is more sensitive to distortions in lower frequency components than higher frequency components. In this paper, we enhance JPEG2000 by introducing a process between wavelet transform and JPEG2000 called JND_SQ. JND_SQ allowed JPEG2000 to maximize the perceptual fidelity instead of PSNR for each transmitted bit. We proposed a perceptual fidelity criterion called JND_PSNR based on the SY JND model. The new criterion is more consistent with human perception than PSNR. The experiment results show that JND_JPEG2000 are better than JPEG2000 in terms of JND_PSNR. The JND_SQ process can efficiently quantize the wavelet coefficient to zeros, which can be further utilized to improve the speed of JPEG2000. Finally, JND_SQ can be turned off if the original JPEG2000 is desired.

摘 要..................................................................i
Abstract................................................................ii
誌 謝.................................................................iii
目 錄..................................................................iv
表目錄..................................................................vi
圖目錄................................................................viii
第一章 緒論.............................................................1
1.1 研究背景與研究動機...................................................1
1.2 研究目標與方法.......................................................1
1.3 論文主要的貢獻.......................................................2
1.4 各章提要.............................................................3
第二章 文獻回顧與探討...................................................4
2.1 人類視覺特性JND in Wavelet Domain....................................4
2.1.1 頻率JND的量測......................................................4
2.1.2 影像之小波分解.....................................................7
2.1.3 小波轉換係數的選取................................................10
2.1.4 WYSV的JND模型[6]..................................................12
2.2 JND影像品質的量測JND_PSNR...........................................13
2.3 JPEG2000基本介紹....................................................15
第三章 JPEG2000影像壓縮標準與演算法實現................................17
3.1 JPEG2000架構........................................................17
3.2前置處理(Preprocessing)..............................................18
3.3離散小波轉換(Discrete Wavelet Transformation)........................18
3.4量化(Quantization)...................................................20
3.5最佳化區塊壓縮編碼(Embedded Block Coding with Optimized Truncations).21
3.6 JPEG2000演算法之實現................................................23
第四章 應用人類視覺模型於JPEG2000之研究................................25
4.1 應用人類視覺模型於JPEG2000..........................................25
4.1.1 JND_JPEG2000演算法組織架構........................................25
4.1.2 JND_SQ純量量化....................................................26
4.1.3 R-D Performance性能評估與比較.....................................27
4.1.4 JND_SQ量化後非零係數之比較........................................34
4.2. VLLCVD[22]之品質評估方式...........................................36
4.2.1 VLLCVD觀測條件....................................................36
4.2.2 視覺無失真之切換檢驗方法..........................................37
4.2.3 臨界無失真距離為基礎之主觀影像品質評估............................37
4.2.4 檢驗JND視覺模型...................................................39
4.2.5 VLLCVD性能評估與比較..............................................40
4.3. JPEG2000與JND_JPEG2000之計算時間比較...............................49
4.3.1 測試環境參數及評估方式............................................50
4.3.2 編解碼時間改善幅度之比較結果......................................50
4.3.3 編解碼時間性能評估與討論..........................................57
第五章 結論與未來研究方向..............................................58
參考文獻................................................................59
Appendix A1.............................................................61
JND measurements for horizontal frequency test pattern..................61
Appendix A2.............................................................62
JND measurements for Vertical frequency test pattern....................62
Appendix A3.............................................................63
JND measurements for diagonal frequency test pattern....................63

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