Error - Index exceeds matrix dimensions..?

Im supposed to do the thresholding for a single row in an image spliting in to 5parts seperately and once it is done Im supposed to plot the all the parts together. when I run this prog, it shows Index exceeds matrix demension.... what am i supposed to do and where am I supposed to alter the code?? Somebody help me... Thank you......

I = imread('D:\1st Semester\Image analysis project\particles.tif');

B= fspecial('motion',33);

C= imfilter (I,B,'symmetric');

row1 = C(500,:);

[y z] = size (row1);

v = zeros(1,z)

for x = 1:500:z;

      level = graythresh(row1(1,x) : row1(1,x+500));
      BW = 255 * im2bw((row1(1,x) : row1(1,x+500)),level);

end

v(1,x:x+500) = BW(1,x:x+500)

figure;

hold on

plot (row1);

plot (BW,'g')

hold off

[Chandra Kurniawan]

What are the size of I?

[Jhay]

[y z] = size (row1)

which gives you,

y = 1

z = 2391

Answer 1

[Walter Roberson]

Your line

for x = 1:500:z

should be

for x = 1:500:z-500

Your z is the number of columns in row1, so with your original code x could be as high as the number of columns, but you then try to index the array up to column x+500

By the way: are you sure you want to be doing overlapping calculations? x = 1 the first time, so you access up to row1(1,1+500), which is row1(1,501) . Then the second time through the loop, x = 501, and you access 501 through 1001 which duplicates the access at 501.

I would suggest that you also consider whether you want to be creating vectors whose length depend upon the contents of the row. row1(1,x):row1(1,x+500) does not access row1 x through x+500: instead it looks into row1(1,x) and looks into row1(x,x+500) and uses those as the bounds for the ":" operator. Perhaps you instead want row1(1,x:x+500) ? (or, more likely, row1(1,x:x+499) ?)

Answer 2

[Jhay]

Overlapping should not be there. Thanks for saying this.. And why should I take x = 1:500:z-500 since I need all the values till the end of the column??? But I need to access row1 x through x+499 and then combining all parts together finally..

[y z] = size (row1)

which gives you,

y = 1 z = 2391

I = imread('D:\1st Semester\Image analysis project\particles.tif');

B= fspecial('motion',33);

C= imfilter (I,B,'symmetric');

row1 = C(500,:);

[y z] = size (row1);

v = zeros(1,z)

for x = 1:500:z;

      level = graythresh(row1(1,x:x+499));
      BW = 255 * im2bw((row1(1,x:x+499)),level);
end

v(1,x:x+499) = BW(1,x:x+499)

figure;

hold on

plot (row1);

plot (BW,'g')

hold off

[Walter Roberson]

Thinking again, z-500 is not needed after all.

[Jhay]

ya you are right.. z-100 is not at all needed...

Answer 3

[Jhay]

No I dint mean in the way you mentioned. HOw did you given the values for x roughly as 2001???

I have initiated a vector with zeros initially to the length of z (no. of columns) which is

v = zeros(1,z)

Now substituting the values of BW(1,x:x+499) in the respective places in the v(1,x:x+499)