Direction histogram: novel discriminative global feature for Thai offline handwritten OCR

Abstract

The image feature used for classification is a crucial part of a character recognition system. To achieve a high accuracy of offline handwriting recognition, the feature should capture the essence of differences including the differences between different characters and the differences between different drawings of the same character. In this paper, we present a novel image feature called direction histogram (DH) and a feature extraction algorithm called bag of histogram (BoH). Unlike the traditional pre-defined feature, DH was designed based on the nature of language and the variation of writing styles. DH is, therefore, a global feature that represents pixel density in all directions around each center. BoH was introduced as it tolerates to thickness and curve variation and ignores the curve connectivity (if any). Fifty-two datasets, each containing 30 drawings of 80 Thai characters, are used for training our neural network, and the original, thick, and distorted handwriting datasets are used for testing. The recognition system with our proposed DH and BoH feature extraction algorithm yielded higher recognition accuracy compared to the convolutional neural network.