I'd threshold the image to get a mask, then scan across column by column getting the first row and last row. Something like
mask = grayImage > someThreshold;
[rows, columns] = size(mask);
topRows = nan(1, columns);
bottomrows = nan(1, columns);
for col = 1 : columns
t = find(mask(:, col), 1, 'first');
if ~isempty(t)
topRows(col) = 1;
bottomRows(col) = find(mask(:, col), 1, 'last');
end
end
hold on;
plot(topRows, 'w-', 'LineWidth', 5);
plot(bottomRows, 'n-', 'LineWidth', 5);
adapt as needed.
If you really can't figure it out, then attach your original image (not a screenshot with tickmarks, etc.).
