## how to plot gray-level value versus image height

on 16 Jan 2013

### Thorsten (view profile)

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....

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### Thorsten (view profile)

on 16 Jan 2013

```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')
```

Elysi Cochin

### Elysi Cochin (view profile)

on 17 Jan 2013

thank u sir for ur reply.... sir i got the top line R1 but for R2 error is being displayed as......

??? Error using ==> line

Vectors must be the same lengths.

Error in ==> Thorsten at 33

line(xlim, [R2 R2], 'Color', 'y')

what should i do sir to rectify this error... please do reply sir.... sir the lines R1 and R2 should be plotted on Iorg so i changed to

```    subplot(2,3,6)
imshow(Iorg)
line(xlim, [R1 R1], 'Color', 'y')
line(xlim, [R2 R2], 'Color', 'y')```

then also line R2 is not getting displayed sir.... please do reply sir...

Walter Roberson

### Walter Roberson (view profile)

on 17 Jan 2013

Please show size(R1) and size(R2) and size(s)

Elysi Cochin

### Elysi Cochin (view profile)

on 17 Jan 2013

why sir.....

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