MATLAB: How to plot gray-level value versus image height

image processing

i have uploaded an image in the link
http://img28.imageshack.us/img28/5363/r1r2.png
in that fig(b) says to plot gray-level value versus image height…. how to plot gray-level value versus image height as shown in that figure(b) and how to get those values R1 and R2 from that… please do reply sir…. i need to get the region between R1 and R2 and draw lines in R1 and R2 as in figure(c) and display that much portion in another figure….. please do reply….

Best Answer

Iorg = imread('./../../Downloads/r1r2.png');
I = rgb2gray(Iorg(58:242, 60:198, :));
s = sum(I');
[notused R1] = max(s);
minthreshold = 30;
R2 = min(find(s  < minthreshold));
subplot(2, 3, [1:3]), imshow(Iorg)
subplot(2,3,4), imshow(I)
subplot(2,3,5),
% plot vertical histogram
N = numel(s);
for i=1:N, line([0 s(i)], N-[i i]+1), end
axis tight
set(gca, 'PlotBoxAspectRatio', [1 size(I,1)/size(I, 2) 1])
xlabel('Gray-level value')
ylabel('Image height')
subplot(2,3,6)
imshow(I)
line(xlim, [R1 R1], 'Color', 'y')
line(xlim, [R2 R2], 'Color', 'y')
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