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function xc = bayer2rgb(xb, M, N, method)
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%BAYER2RGB Summary of this function goes here
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% Detailed explanation goes here
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% Initializes the struct that's going to store the RGB image
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xc = struct;
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xc.red = zeros(M, N);
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xc.green = zeros(M, N);
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xc.blue = zeros(M, N);
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% Initializes helper variables
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bayerPatternDimY = size(xb, 1);
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bayerPatternDimX = size(xb, 2);
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% Calculates the distance between two grid points for both axes
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gridPointsStepLengthY = (bayerPatternDimY - 1) / (M - 1);
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gridPointsStepLengthX = (bayerPatternDimX - 1) / (N - 1);
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% Calculates the coordinates of the grid points for both axes
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gridPointsCoordinatesY = (1:gridPointsStepLengthY:bayerPatternDimY)';
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gridPointsCoordinatesX = (1:gridPointsStepLengthX:bayerPatternDimX)';
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if (strcmp(method, 'nearest'))
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% Determines the indeces of the even rows of the original image
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% that are closest to each ordinate of the new image grid
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gridPointYmod2 = mod(gridPointsCoordinatesY, 2) >= 1;
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nearestEvenRow = floor(gridPointsCoordinatesY);
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nearestEvenRow(gridPointYmod2) = nearestEvenRow(gridPointYmod2)+1;
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nearestEvenRow(nearestEvenRow > bayerPatternDimY) = ...
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nearestEvenRow(nearestEvenRow > bayerPatternDimY) - 2;
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% Determines the indeces of the odd rows of the original image that
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% are closest to each ordinate of the new image grid
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nearestOddRow = floor(gridPointsCoordinatesY);
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nearestOddRow(~gridPointYmod2) = nearestOddRow(~gridPointYmod2)+1;
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nearestOddRow(nearestOddRow > bayerPatternDimY) = ...
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nearestOddRow(nearestOddRow > bayerPatternDimY) - 2;
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% Determines the indeces of the even columns of the original image
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% that are closest to each abscissa of the new image grid
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gridPointXmod2 = mod(gridPointsCoordinatesX, 2) >= 1;
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nearestEvenCol = floor(gridPointsCoordinatesX);
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nearestEvenCol(gridPointXmod2) = nearestEvenCol(gridPointXmod2)+1;
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nearestEvenCol(nearestEvenCol > bayerPatternDimX) = ...
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nearestEvenCol(nearestEvenCol > bayerPatternDimX) - 2;
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% Determines the indeces of the odd columns of the original image
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% that are closest to each abscissa of the new image grid
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nearestOddCol = floor(gridPointsCoordinatesX);
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nearestOddCol(~gridPointXmod2) = nearestOddCol(~gridPointXmod2)+1;
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nearestOddCol(nearestOddCol > bayerPatternDimX) = ...
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nearestOddCol(nearestOddCol > bayerPatternDimX) - 2;
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% Determines the indeces of the rows (even or odd) of the original
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% image that are closest to each ordinate of the new image grid
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totalNearestRow = round(gridPointsCoordinatesY);
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% Determines the indeces of the columns (even or odd) of the
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% original image that are closest to each abscissa of the new image
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totalNearestCol = round(gridPointsCoordinatesX);
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% Closest neighbors for red and blue can be determined by observing
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% the Bayer pattern
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xc.red = xb(nearestOddRow, nearestEvenCol);
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xc.blue = xb(nearestEvenRow, nearestOddCol);
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for currentRow = 1:M
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for currentCol = 1:N
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if ((mod(totalNearestRow(currentRow), 2) == 0 && ...
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mod(totalNearestCol(currentCol), 2)) ~= 0 || ...
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(mod(totalNearestRow(currentRow), 2) ~= 0 && ...
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mod(totalNearestCol(currentCol), 2) == 0))
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% This point of the original image doesn't contain
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% information about the green colour
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% Calculates the vertical displacement of the two
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% diagonal lines that cross this point
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b1 = totalNearestRow(currentRow) - ...
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totalNearestCol(currentCol);
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b2 = totalNearestRow(currentRow) + ...
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totalNearestCol(currentCol);
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% Calculates the ordinate of the two diagonals at the
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% abscissa of the current point (currentCol)
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y1 = gridPointsCoordinatesX(currentCol) + b1;
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y2 = -gridPointsCoordinatesX(currentCol) + b2;
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% Initializes temporary coordinates of the point which
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% will be selected as the closest one
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fixedNearestRow = totalNearestRow(currentRow);
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fixedNearestCol = totalNearestCol(currentCol);
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% Checks the relative position between the point and
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% the two diagonals
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if (gridPointsCoordinatesY(currentRow) >= y1 && ...
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gridPointsCoordinatesY(currentRow) >= y2)
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fixedNearestRow = totalNearestRow(currentRow) - 1;
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elseif (gridPointsCoordinatesY(currentRow) < y1 && ...
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gridPointsCoordinatesY(currentRow) < y2)
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fixedNearestRow = totalNearestRow(currentRow) + 1;
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elseif (gridPointsCoordinatesY(currentRow) >= y1 && ...
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gridPointsCoordinatesY(currentRow) < y2)
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fixedNearestCol = totalNearestCol(currentCol) - 1;
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elseif (gridPointsCoordinatesY(currentRow) < y1 && ...
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gridPointsCoordinatesY(currentRow) >= y2)
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fixedNearestCol = totalNearestCol(currentCol) + 1;
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end
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if (fixedNearestRow < 1)
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% Fix for the marginal first row case
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xc.green(currentRow, currentCol) = ...
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xb(1, fixedNearestCol - 1);
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else
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xc.green(currentRow, currentCol) = ...
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xb(fixedNearestRow, fixedNearestCol);
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end
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else
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xc.green(currentRow, currentCol) = ...
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xb(totalNearestRow(currentRow), ...
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totalNearestCol(currentCol));
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end
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end
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end
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elseif (strcmp(method, 'linear'))
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% Calculates helper variables
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flooredCoordinatesY = floor(gridPointsCoordinatesY);
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flooredCoordinatesX = floor(gridPointsCoordinatesX);
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% Calculates the ordinate of the upper couple of nearest points
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% that will be used in the interpolation for the blue colour
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upperBlueY = flooredCoordinatesY;
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upperBlueY(mod(upperBlueY, 2) ~= 0) = ...
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upperBlueY(mod(upperBlueY, 2) ~= 0) - 1;
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upperBlueY = upperBlueY + 2;
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% Calculates the ordinate of the upper couple of nearest points
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% that will be used in the interpolation for the red colour
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upperRedY = flooredCoordinatesY;
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upperRedY(mod(upperRedY, 2) == 0) = ...
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upperRedY(mod(upperRedY, 2) == 0) - 1;
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upperRedY = upperRedY + 2;
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% Calculates the abscissa of the left couple of nearest points that
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% will be used in the interpolation for the blue colour
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leftBlueX = flooredCoordinatesX;
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leftBlueX(mod(leftBlueX, 2) == 0) = ...
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leftBlueX(mod(leftBlueX, 2) == 0) - 1;
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leftBlueX = leftBlueX + 2;
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% Calculates the abscissa of the left couple of nearest points that
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% will be used in the interpolation for the red colour
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leftRedX = flooredCoordinatesX;
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leftRedX(mod(leftRedX, 2) ~= 0) = ...
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leftRedX(mod(leftRedX, 2) ~= 0) - 1;
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leftRedX = leftRedX + 2;
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% Determines the indeces of the rows (even or odd) of the original
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% image that are closest to each ordinate of the new image grid
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centerPointRow = round(gridPointsCoordinatesY);
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% Determines the indeces of the columns (even or odd) of the
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% original image that are closest to each abscissa of the new image
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centerPointCol = round(gridPointsCoordinatesX);
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% Adds a padding to the original image, replicating the last two
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% rows and columns of each egde
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xbPadded = [xb(:, end - 1) xb(:, end - 2) xb xb(:, end - 2) ...
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xb(:, end - 1)];
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xbPadded = [xbPadded(1, :); xbPadded(2, :); xbPadded; ...
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xbPadded(end - 2, :); xbPadded(end - 1, :)];
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for currentRow = 1:M
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lowerInterpPointBlue = ...
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((leftBlueX + 2 - gridPointsCoordinatesX) / 2)' .* ...
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xbPadded(upperBlueY(currentRow) + 2, leftBlueX) + ...
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((gridPointsCoordinatesX - leftBlueX) / 2)' .* ...
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xbPadded(upperBlueY(currentRow) + 2, leftBlueX + 2);
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upperInterpPointBlue = ...
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((leftBlueX + 2 - gridPointsCoordinatesX) / 2)' .* ...
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xbPadded(upperBlueY(currentRow), leftBlueX) + ...
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((gridPointsCoordinatesX - leftBlueX) / 2)' .* ...
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xbPadded(upperBlueY(currentRow), leftBlueX + 2);
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xc.blue(currentRow, :) = ...
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((upperBlueY(currentRow) - ...
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gridPointsCoordinatesY(currentRow)) / 2) * ...
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lowerInterpPointBlue + ...
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((gridPointsCoordinatesY(currentRow) - ...
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upperBlueY(currentRow) + 2) / 2) * ...
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upperInterpPointBlue;
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lowerInterpPointRed = ...
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((leftRedX + 2 - gridPointsCoordinatesX) / 2)' .* ...
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xbPadded(upperRedY(currentRow) + 2, leftRedX) + ...
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((gridPointsCoordinatesX - leftRedX) / 2)' .* ...
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xbPadded(upperRedY(currentRow) + 2, leftRedX + 2);
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upperInterpPointRed = ...
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((leftRedX + 2 - gridPointsCoordinatesX) / 2)' .* ...
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xbPadded(upperRedY(currentRow), leftRedX) + ...
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((gridPointsCoordinatesX - leftRedX) / 2)' .* ...
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xbPadded(upperRedY(currentRow), leftRedX + 2);
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xc.red(currentRow, :) = ...
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((upperRedY(currentRow) - gridPointsCoordinatesY(currentRow)) / 2) * ...
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lowerInterpPointRed + ...
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((gridPointsCoordinatesY(currentRow) - upperRedY(currentRow) + 2) / 2) * ...
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upperInterpPointRed;
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for currentCol = 1:N
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if ((mod(centerPointRow(currentRow), 2) == 0 && ...
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mod(centerPointCol(currentCol), 2)) == 0 || ...
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(mod(centerPointRow(currentRow), 2) ~= 0 && ...
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mod(centerPointCol(currentCol), 2) ~= 0))
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% This point of the original image DOES contain
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% information about the green colour
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% Calculates the vertical displacement of the two
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% diagonal lines that cross this point
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b1 = centerPointRow(currentRow) - ...
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centerPointCol(currentCol);
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b2 = centerPointRow(currentRow) + ...
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centerPointCol(currentCol);
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% Calculates the ordinate of the two diagonals at the
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% abscissa of the current point (currentCol)
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y1 = gridPointsCoordinatesX(currentCol) + b1;
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y2 = -gridPointsCoordinatesX(currentCol) + b2;
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% Initializes temporary coordinates of the point which
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% will be selected as the center
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fixedCenterPointRow = centerPointRow(currentRow);
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fixedCenterPointCol = centerPointCol(currentCol);
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% Checks the relative position between the point and
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% the two diagonals
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if (gridPointsCoordinatesY(currentRow) >= y1 && ...
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gridPointsCoordinatesY(currentRow) >= y2)
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fixedCenterPointRow = centerPointRow(currentRow) - 1;
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elseif (gridPointsCoordinatesY(currentRow) < y1 && ...
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gridPointsCoordinatesY(currentRow) < y2)
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fixedCenterPointRow = centerPointRow(currentRow) + 1;
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elseif (gridPointsCoordinatesY(currentRow) >= y1 && ...
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gridPointsCoordinatesY(currentRow) < y2)
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fixedCenterPointCol = centerPointCol(currentCol) - 1;
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elseif (gridPointsCoordinatesY(currentRow) < y1 && ...
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gridPointsCoordinatesY(currentRow) >= y2)
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fixedCenterPointCol = centerPointCol(currentCol) + 1;
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end
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if (fixedCenterPointRow < 1)
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% Fix for the marginal first row case
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fixedCenterPointRow = 1;
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fixedCenterPointCol = fixedCenterPointCol - 1;
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end
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xc.green(currentRow, currentCol) = ...
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tiltedInterp(gridPointsCoordinatesX(currentCol), ...
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gridPointsCoordinatesY(currentRow), ...
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fixedCenterPointCol, fixedCenterPointRow, xbPadded);
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else
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xc.green(currentRow, currentCol) = ...
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tiltedInterp(gridPointsCoordinatesX(currentCol), ...
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gridPointsCoordinatesY(currentRow), ...
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centerPointCol(currentCol), ...
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centerPointRow(currentRow), xbPadded);
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end
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end
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end
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end
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% Combines colours to a single image array and shows the result
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rgbImage = cat(3, xc.blue, xc.green, xc.red);
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figure();
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imshow(rgbImage);
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end
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function value = tiltedInterp(xw, yw, xc, yc, xbPadded)
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% Calculates the vertical displacement of the main diagonal that
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% crosses this point
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bw = yw - xw;
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% Calculates the abscissas of the points of intersection
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x1 = (yc + xc - 1 - bw) / 2;
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%x2 = (yc + xc + 1 - bw) / 2;
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% Calculates perpendicular distance of point w to the line connecting
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% the lower point and the left point
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dist = sqrt((x1 - xw) ^ 2 + (x1 + bw - yw) ^ 2);
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% Calculates the lengths of the upper parts of the lines connecting the
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% points
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h1 = sqrt(((xc - 1 - xw) ^ 2 + (yc - yw) ^ 2) - dist ^ 2);
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lowerLeftInterpPoint = ...
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((sqrt(2) - h1) / sqrt(2)) * ...
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xbPadded(yc + 2, xc - 1 + 2) + ...
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(h1 / sqrt(2)) * ...
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xbPadded(yc + 1 + 2, xc + 2);
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upperRightInterpPoint = ...
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((sqrt(2) - h1) / sqrt(2)) * ...
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xbPadded(yc - 1 + 2, xc + 2) + ...
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(h1 / sqrt(2)) * ...
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xbPadded(yc + 2, xc + 1 + 2);
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value = ...
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(sqrt(2) - dist) / sqrt(2) * lowerLeftInterpPoint + ...
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dist / sqrt(2) * upperRightInterpPoint;
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end
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