Global_Thresholding

clear, clc, close all

% Load test image
img = im2double(imread('paper.png'));

% Perform global thresholding with Otsu's method
level = graythresh(img);
globalBwImg = im2bw(img, level);

% Decide local thresholding parameters
[row col] = size(img);
stepSize = 16;
tileSize = 32;
varThresh = 0.0005;

% Perform locally adaptive thresholding
localBwImg = zeros(row, col);
uniformMask = zeros(row, col);
threshIm = zeros(row / stepSize, col/ stepSize);
for i = 1: row / stepSize

% Get indices for row
rowStep = (i - 1) * stepSize + 1 : i * stepSize;
rowTile = (i - 1) * stepSize + 1 : (i + 1) * stepSize;
if i == row / stepSize
rowTile = (i-2) * stepSize + 1 : i * stepSize;
end

% Calculate Otsu's threshold for row
rowThresh = graythresh(img(rowTile, :));
for j = 1: col / stepSize

% Get indices for column
colStep = (j - 1) * stepSize + 1 : j * stepSize;
colTile = (j - 1) * stepSize + 1 : (j + 1) * stepSize;
if j == col / stepSize
colTile = (j - 2) * stepSize + 1 : j * stepSize;
end

% Calculate local variance
step = img(rowStep, colStep);
varStep = var(step(:));

% Calculate local Otsu's threshold
tile = img(rowTile, colTile);
localThresh = graythresh(tile);

% Threshold based on local Otsu's threshold
if (varStep > varThresh)
localBwImg(rowStep, colStep) = im2bw(step, localThresh);
uniformMask(rowStep, colStep) = ones(stepSize, stepSize);
threshIm(i, j) = localThresh;

% Threshold based on local mean
else
localMean = mean(tile(:));
threshIm(i, j) = 0;
if (localMean > min(rowThresh,level))
localBwImg(rowStep, colStep) = ones(stepSize, stepSize);
else
localBwImg(rowStep, colStep) = zeros(stepSize, stepSize);
end
uniformMask(rowStep, colStep) = zeros(stepSize, stepSize);
end
end % j
end % i