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  • 學位論文

使用具鑑別力原型之物件辨識方法

Object Recognition Using Discriminative Prototypes

指導教授 : 李瑞庭

摘要


許多物件辨識方法利用物件上的顯著區域(salient region)增進它們辨識形變後或被遮蔽物件的穩定性。但如果不同的物件擁有相同或是類似的顯著區域,這些方法將難以辨識這些物件。此外,如果沒有非常仔細地挑選顯著區域,辨識的效果也將會大打折扣。 因此在本論文中,我們利用具鑑別力的區域(discriminative region)來進行物件辨識。我們提出的方法包括訓練及測試兩階段。在訓練階段,我們利用不同大小的移動視窗(sliding window)在訓練物件上循序取出一個一個區域。接著將每個區域轉換成一個特徵向量,而每一個特徵向量包括color histogram、intensity moments、affine invariant moments及SIFT descriptor四種特徵。然後,我們應用Crisp Construction Process演算法,從訓練特徵向量中,為每一個訓練物件取出一組原型(prototype)。所取出的原型可用來區分此物件與其他物件,也就是說,這些原型即是此物件上具鑑別力的區域。在測試階段,我們同樣使用移動視窗在測試物件上循序取出一個一個區域,然後,將每個區域轉成特徵向量並找出它最接近的原型,亦即測試物件上此區域屬於該原型所代表的區域。因此,我們可以為每個訓練物件與該測試物件計算一個分數,以代表它們之間的相似程度。我們利用訓練物件的面積、測試物件的面積、測試物件上屬於訓練物件的區域的面積及該訓練物件上為測試物件所屬的區域的面積來計算分數,然後將測試物件歸屬於得分最高的訓練物件。另外,我們亦採用C4.5決策樹(C4.5 decision tree)以加速辨識流程。我們的方法對於形變後、被遮蔽、有光影變化及複雜背景的物件具有極佳的辨識能力。對於被噪訊干擾及受JPEG壓縮過後的影像也有很好的辨識能力。 實驗結果顯示,我們的方法在辨識COIL-100及ZuBuD資料庫上,表現均優於其他物件辨識方法。若採用C4.5決策樹加速,辨識速度可提升五至八倍。

並列摘要


Many previously proposed methods of object recognition use the salient regions of the objects to improve their robustness to distortion and occlusion. The methods based on salient regions inevitably encounter the difficulties if several different objects share identical or similar salient regions. Moreover, if the salient regions cannot be selected very carefully, the performance will be deteriorated incredibly. Therefore, in this dissertation, we propose a method which uses discriminative regions rather than salient regions to perform object recognition. Our proposed method consists of two phases, namely, training and testing. In the training phase, we first use sliding windows of different sizes to retrieve a number of regions from an object. For each region retrieved, we extract a feature vector, each of which contains four types of descriptors, namely, color histogram, intensity moments, affine invariant moments, and SIFT descriptor. Then, the Crisp Construction Process algorithm is applied to these training feature vectors to generate a number of prototypes for each model object. The prototypes of a model object can be used to discriminate it from the others. That is, the prototypes are the discriminative regions of the model object. In the testing phase, we also use sliding windows to extract the feature vectors of a test object. For each feature vector extracted, we find its nearest prototype and assign it to the discriminative region represented by the nearest prototype. Then, we compute a score for each model object according to the area of the model object, the area of the test object, the area covered by the feature vectors that are assigned to the model object, and the area covered by the assigned discriminative regions. The test object is considered as the model object with the highest score. Moreover, we adopt C4.5 decision tree to speed up the recognition process. Our proposed method is robust to distortion, occlusion, illumination changes, and cluttered background. Noisy and compressed images can also be well recognized. The experimental results show that our proposed method outperforms the comparing methods in the COIL-100 and ZuBuD datasets in terms of recognition rates. By adopting the C4.5 decision tree, the recognition process becomes 5 - 8 faster.

參考文獻


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