低解析度印刷數字之辨識

Abstract

儘管數字影像辨識已經算是一個成熟的技術了，但對於低解析度數字影像的處理，卻仍是一個較少人研究和討論的方向。在這篇論文裡頭，我們發展了一個高速發票印刷檢測系統，並針對印刷中之發票號碼作自動辨識。其中，我們探討了幾個具有挑戰性的問題，如：高速印刷檢測系統的設計、發票影像中數字區塊的切割與背景網點的消除，低解析度數字影像的辨識等。為了解決這些問題，我們提出了最小灰階值分析法（Minimal Gray-level Analysis），來處理發票影像中，數字區塊的切割、網點消除和影像強化等前處理的部分。另外，對於每個只有 8 x 8 的低解析度數字影像，我們應用所提出的列處理法（Row-based Method）來擷取其特徵，然後，再以樹狀辨識器來做辨識。依據我們在實驗室中雛形系統的測試結果，可以達到 95% 以上的辨識率。

In this paper, we develop an on-line inspecting system for invoice printing and introduce some techniques to automatically recognize the printed digits on the invoices. The poor quality of an invoice image, the textured background, and the low resolution of each printed digit make the research challenging. To overcome these problems, a robust method based on a minimal gray-level analysis is proposed to preprocess the invoice images. The preprocessing includes the number block extraction, textured background removal, and digit image enhancement. For each digit image of 8(8 pixels, a row-based method is developed to extract the features of the digit, which is then applied to a tree classifier for recognition. For the prototype system developed in the laboratory, a recognition rate of 95% can be achieved.