Just scan across the thresholded image finding the first and last rows where you have a pixel. Then you might have to get rid of outliers, maybe with a median filter. Then compute the area and divide by the width. Something like (untested):
[rows, columns, numberOfColorChannels] = size(grayImage);
mask = grayImage > someThreshold.
topRows = zeros(1, columns);
bottomRows = zeros(1, columns);
for col = 1 : columns
t = find(mask(:, col), 1, 'first');
if ~isempty(t)
topRows(col) = t;
bottomRows(col) = find(mask(:, col), 1, 'last');
end
end
x = 1 : columns;
hold on;
plot(x, topRows, 'r-', 'LineWidth', 2);
plot(x, bottomRows, 'r-', 'LineWidth', 2);
% Get heights as function of column.
heights = bottomRows - topRows;
% That is the area of each column.
% Divide by the number of columns to get the mean height.
meanHeight = sum(heights) / columns;
If you still need help, attach the original image (without any lines or annotations).
