function [ swtMap ] = swt( im, searchDirection )%swt Preforms stoke width transform on input image%   A novel image operator that seeks to find the value of stroke width%   for each image pixel.  It‘s use is meant for the task of text%   detection in natural images.%%   im = RGB input image of size m x n x 3%   searchDirection = gradient direction is either 1 to detect dark text on light%   background or -1 to detect light text on dark background.%%   swtMap = resulting mapping of stroke withs for image pixels% Convert image to gray scaleim = im2double(rgb2gray(im));%figure, imshow(im), title(‘Black and White Image‘);% Find edges using canny edge dectoredgeMap = edge(im, ‘canny‘);%figure, imshow(edgeMap), title(‘Edges Using Canny‘);% Get all edge pixel postitions[edgePointRows, edgePointCols] = find(edgeMap);% Find gradient horizontal and vertical gradientsobelMask = fspecial(‘sobel‘);dx = imfilter(im,sobelMask);dy = imfilter(im,sobelMask‘);%figure, imshow(dx, []), title(‘Horizontal Gradient Image‘);%figure, imshow(dy, []), title(‘Vertical Gradient Image‘);% Initializing matrix of gradient directiontheta = zeros(size(edgeMap,1),size(edgeMap,2));% Calculating theta, gradient direction, for each pixel on the image.% ***This can be optimized by using edgePointCols and edgePointRows% instead.***for i=1:size(edgeMap,1)    for j=1:size(edgeMap,2)        if edgeMap(i,j) == 1            theta(i,j) = atan2(dy(i,j),dx(i,j));        end    endend% Getting size of the image[m,n] = size(edgeMap);% Initializing Stoke Width array with infinityswtMap = zeros(m,n);for i=1:m    for j=1:n        swtMap(i,j) = inf;    endend% Set the maximum stroke width, this number is variable for now but must be% made to be more dynamic in the futuremaxStrokeWidth = 350;% Initialize container for all stoke points foundstrokePointsX = zeros(size(edgePointCols));strokePointsY = zeros(size(strokePointsX));sizeOfStrokePoints = 0;% Iterate through all edge points and compute stoke widthsfor i=1:size(edgePointRows)    step = 1;    initialX = edgePointRows(i);    initialY = edgePointCols(i);    isStroke = 0;    initialTheta = theta(initialX,initialY);    sizeOfRay = 0;    pointOfRayX = zeros(maxStrokeWidth,1);    pointOfRayY = zeros(maxStrokeWidth,1);        % Record first point of the ray    pointOfRayX(sizeOfRay+1) = initialX;    pointOfRayY(sizeOfRay+1) = initialY;        % Increase the size of the ray    sizeOfRay = sizeOfRay + 1;        % Follow the ray    while step < maxStrokeWidth        nextX = round(initialX + cos(initialTheta) * searchDirection * step);        nextY = round(initialY + sin(initialTheta) * searchDirection * step);                step = step + 1;                % Break loop if out of bounds.  For some reason this is really        % slow.        if nextX < 1 | nextY < 1 | nextX > m | nextY > n            break        end                % Record next point of the ray        pointOfRayX(sizeOfRay+1) = nextX;        pointOfRayY(sizeOfRay+1) = nextY;                % Increase size of the ray        sizeOfRay = sizeOfRay + 1;                % Another edge pixel has been found        if edgeMap(nextX,nextY)                        oppositeTheta = theta(nextX,nextY);                        % Gradient direction roughtly opposite            if abs(abs(initialTheta - oppositeTheta) - pi) < pi/2                isStroke = 1;                strokePointsX(sizeOfStrokePoints+1) = initialX;                strokePointsY(sizeOfStrokePoints+1) = initialY;                sizeOfStrokePoints = sizeOfStrokePoints + 1;            end                        break        end    end        % Edge pixel is part of stroke    if isStroke                % Calculate stoke width        strokeWidth = sqrt((nextX - initialX)^2 + (nextY - initialY)^2);                % Iterate all ray points and populate with the minimum stroke width        for j=1:sizeOfRay            swtMap(pointOfRayX(j),pointOfRayY(j)) = min(swtMap(pointOfRayX(j),pointOfRayY(j)),strokeWidth);        end    endend%figure, imshow(swtMap, []), title(‘Stroke Width Transform: First Pass‘);% Iterate through all stoke points for a refinement pass.  Refer to figure% 4b in the paper.for i=1:sizeOfStrokePoints    step = 1;    initialX = strokePointsX(i);    initialY = strokePointsY(i);    initialTheta = theta(initialX,initialY);    sizeOfRay = 0;    pointOfRayX = zeros(maxStrokeWidth,1);    pointOfRayY = zeros(maxStrokeWidth,1);    swtValues = zeros(maxStrokeWidth,1);    sizeOfSWTValues = 0;        % Record first point of the ray    pointOfRayX(sizeOfRay+1) = initialX;    pointOfRayY(sizeOfRay+1) = initialY;        % Increase the size of the ray    sizeOfRay = sizeOfRay + 1;        % Record the swt value of first stoke point    swtValues(sizeOfSWTValues+1) = swtMap(initialX,initialY);    sizeOfSWTValues = sizeOfSWTValues + 1;        % Follow the ray    while step < maxStrokeWidth        nextX = round(initialX + cos(initialTheta) * searchDirection * step);        nextY = round(initialY + sin(initialTheta) * searchDirection * step);                step = step + 1;                % Record next point of the ray        pointOfRayX(sizeOfRay+1) = nextX;        pointOfRayY(sizeOfRay+1) = nextY;                % Increase size of the ray        sizeOfRay = sizeOfRay + 1;                % Record the swt value of next stoke point        swtValues(sizeOfSWTValues+1) = swtMap(nextX,nextY);        sizeOfSWTValues = sizeOfSWTValues + 1;                % Another edge pixel has been found        if edgeMap(nextX,nextY)            break        end    end        % Calculate stoke width as the median value of all swtValues seen.    strokeWidth = median(swtValues(1:sizeOfSWTValues));        % Iterate all ray points and populate with the minimum stroke width    for j=1:sizeOfRay        swtMap(pointOfRayX(j),pointOfRayY(j)) = min(swtMap(pointOfRayX(j),pointOfRayY(j)),strokeWidth);    end    end%figure, imshow(swtMap, []), title(‘Stroke Width Transform: Second Pass‘);end