相位調制應用於光學圖像辨識

Abstract

本論文主要在研究以相位調制代表二維圖像之技術，並探討以相位調制方式進行圖像辨識及異關聯記憶之特性。首先，我們利用液晶顯示板配合光學元件，作為空間相位調制器，研究此空間相位調制系統的相位調制能力及其限制。經由計算與實驗證明，此系統可成功達成二位元之空間相位調制，但由於顯示器之驅動證明，使得液晶示板在０與π相位交界處之振幅與其它位置不相等，這影響到用此液晶顯示板來執行圖像辨識之性能。其次，我們探討此種資訊調制方式之圖像辨識系統性能。由電腦模擬結果得知，相位調制之影像的鑑別率較振幅調制者為佳。光學實驗結果則顯示，在記憶材料置於輸入圖像之成像平面的系統，相位調制確實有較佳的圖像辨識能力；但在記憶材料置於輸入圖像之富氏平面的系統，兩者之差異則不明顯。最後，我們應用相位調制訊號的特性以及相位匹配瀘波器之技術，探討異關聯記憶系統。電腦模擬結果顯示，以體積全像方式來儲存許多對異關聯記憶是可行的，而且相位匹配濾波器可以明顯改善重複儲存多張影像之串音干擾現象。

In this thesis, we investigate optical pattern recognition by using phase modulation of the input images. First, a liquid crystal display (LCD) panel is used for the spatial phase modulator. The phase modulation characteristics of the LCD are studied, both theoretically and experimentally. The results show that binary phase modulation can be achieved by the LCD. However, there is a gray level in light amplitudes at the boundaries between zero and πphases. This phenomenon degrades the image recognition capability of the device. Secondly, we have performed computer simulations and optical experiments for optical pattern recognition of the phase modulated images. Computer simulations show that the phase modulate system has better discrimination capability then that of the amplitude modulated system. Optical experiments show that the phase modulated system has better discrimination capbility if the optical filter is set at the image plane of the input images. Whereas for the case of setting the optical filter at Fourier plane, both the modulated wystems have similr discrimination capabilities. Third, we have applied the technique of phase modulated images and phase only matched filter to study the hetero-associative memory. By using this technique, the cross-talk between different pairs of memories are reduced. And the feasibility of storing multiple-pair of hetero-associative memories in a volume hologram is demonstrated.