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Chinese Character Recognition for Video Presented by: Vincent Cheung Date: 25 October 1999
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Introduction n Many dialects in Chinese, but Chinese Characters is common in anywhere. n Many video programs have Chinese subtitles nowadays n Extract text from digital video programs can help for indexing, searching and retrieval
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Features of Subtitles n Characters are in foreground n They are monochrome n They are rigid, from frame to frame n They are upright n They have size restrictions n They contrast with the background n They appear in clusters at a limited distance aligned to a horizontal line
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Steps to Recognise Text n Clearing the background, removing noise n Segmenting the characters n Recognising them by pattern matching
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Demo Video n A piece of news from ATV about Airport Authority Hong Kong and is reported in Cantonese n In MPEG format n 1... 2... 3... Action!
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MPEG Video n Consisted of a video track and an audio track n Consisted of frames n For video part, a frame is representing a static image
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Steps to Remove Background Agnihotri & Dimitrova Suggested 7 steps procedures: n Channel Separation n Image Enhancement n Edge Detection n Edge Filtering n Character Detection n Text Box Detection n Text Line Detection & Enhancement
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Sample Frame n The 100th frame of the demo video
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Channel Separation n Use Red Channel which gives higher contrast edges n More probably that natural environment are in blue or green Green Channel Red Channel Blue Channel
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Image Enhancement n To filter salt and pepper noise n To sharpen the edges n Quality of our mpeg video is quite good that we no need to take this step
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Edge Detection n Find out the edges from the image n Use a 3x3 matrice mask -1 -1 -1 [ -1 12 -1 ] -1 -1 -1 n Use Sobel Filter instead n edges around text may be broken and not connected
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Sample Edge Image
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Edge Filtering n To remove areas which possibly do not contain text n Characters would give high density of objects, hence high density of edges n Finding out areas with high density of edges which give hints of where the characters located
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Density of edges in horizontal lines
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Filtering the Irrelevant Edges
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Density of Edges in Vertical
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What if the length of subtitle is short?? n Cut the image into certain parts and calculate the density of edges in those areas n Prevent the case if the subtitle is short and cannot give an overall view
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Sample Image Divided in Parts
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Challenges in Chinese Characters Segmentation n Square? n Not Really, they are variable in size!! Having different height and width n e.g.: ( 日, 曰 ) n Lead to some problem in Fixed- Distance Approach Segmentation n More problems if mixed with English, Numbers, and Symbols n e.g. 18 部「 IBM 」電腦
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n Usually written in horizontal way, like English. n Do segmentation like English? n English: each character is horizontally linked n Chinese: may not have such linkage n e.g.: 八, 川 Challenges in Chinese Characters Segmentation
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Character Recognition Pattern Matching n most straight forward n two pattern are compared n by using pattern distance
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Classification for Faster Matching n By blackness (e.g. 一, 鬱 ) n By projection profiles
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Possible Enhancement n Picking out the moving objects by keeping track of a number of consecutive frames n Use of lexicon to choose the most possible character
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Q & A
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