MATLAB车牌汉字识别

function result = letter_compare(ocr_letters, document_letter) % LETTER_COMPARE.M % % function result = letter_compare(ocr_letters, document_letter) % % Parameters: ocr_letters is an array (1..4) of structures % with fields: Mean, Covariance % Subscripts of array mean 1=O 2=E 3=A 4=U % document_letter fields is a structure which has % with fields: Image, EulerNumber, Area, BoundingBox % % This function compares a letter extracted from the image paragraph % to each of the four vowels. Returns the index of the vowel % which the letter from the paragraph matches, if any. % If no vowels match up, return 0. % % Assumptions: % - the letter form the document/paragraph is properly oriented % Calculate the data necessary for the matching perImg = bwperim(document_letter.Image); perArea = bwarea(perImg); compactness = perArea^2/document_letter.Area; moments = invmoments(document_letter.Image); % Calculate the top/bottom area ratio midpoint = floor(document_letter.BoundingBox(4)/2); topPart = document_letter.Image(1:midpoint,:); bottomPart = document_letter.Image((midpoint+1):end,:); partRatio = bwarea(topPart)/bwarea(bottomPart); % Final vector for the doucment image which will be used for comparison vector = [ moments(1) moments(2) moments(3) compactness partRatio ]; % Go through all four letters for i = 1: 4, % Closeness will be Mahalanobis distance without the log term closeness(i) = (vector - ocr_letters(i).Mean)*... inv(ocr_letters(i).Covariance)*... (vector - ocr_letters(i).Mean)'; % Distance is Mahalanobis distance with the log term % The log term equalizes the distance space so that % we can compare which one of the four letters % is closer to the letter extracted from the paragraph distance(i) = closeness(i) + log(det(ocr_letters(i).Covariance)); end % Find one of the vowels with the smallest distance to the document letter minimumDistance = distance(1); closestMatch = 1; for j = 1:4, if distance(j)<minimumDistance minimumDistance = distance(j); closestMatch = j; end end % Now we have to determine if the closest match is noise or not variance = [ ocr_letters(closestMatch).Covariance(1,1) ... ocr_letters(closestMatch).Covariance(2,2) ... ocr_letters(closestMatch).Covariance(3,3) ... ocr_letters(closestMatch).Covariance(4,4) ... ocr_letters(closestMatch).Covariance(5,5) ]; % Standard deviation std = sqrt(variance); matchCloseness = closeness(closestMatch); % Use Mahalanobis distance to figure out the allowed range for % the closeness within which the letter is accepted as a match allowedRange = 6.5*(std) * inv(ocr_letters(closestMatch).Covariance) * (std)'; % Closeness is within allowed interval if (matchCloseness <= allowedRange) % ###################### SECONDARY CHECKS ################ if closestMatch == 1 % It thinks it is an O if (document_letter.EulerNumber ~= 0) % Reject closestMatch = 0; end elseif closestMatch == 2 % It thinks it is an E if (document_letter.EulerNumber ~= 0) % Reject closestMatch = 0; end elseif closestMatch == 3 % It thinks it is an A % Euler# can be 0 or 1 if (document_letter.EulerNumber ~= 0) & ... (document_letter.EulerNumber ~= -1) % Reject closestMatch = 0; end % Ahh, but it might be an S ! % S's have about equal distribution % of weight about their midpoint if (partRatio > 0.87 ) % S rejected because the weight of the top % half is about equal to the wight of the % bottom half closestMatch = 0; end elseif closestMatch == 4 % It thinks it is a U % Euler# can be 0 or 1 if (document_letter.EulerNumber ~=1 ) % Reject closestMatch = 0; end % Also, calculate the Eulers for the top and % bottom slices midpoint = floor(document_letter.BoundingBox(4)/2); topPart = im2bw(document_letter.Image(1:midpoint,:), 0.5); bottomPart = im2bw(document_letter.Image(midpoint+1,:), 0.5); topFeature = imfeature(double(topPart), 'EulerNumber'); bottomFeature = imfeature(double(bottomPart), 'EulerNumber'); topEuler = topFeature(1).EulerNumber; bottomEuler = bottomFeature(1).EulerNumber; % For u's, the top Euler number is 2, and the bottom % part has Euler number of 2 if (topEuler~=2) | (bottomEuler ~= 2) % Can't be an U according to Euler checks closestMatch = 0; end end result = closestMatch; else result = 0; end