ERROR : Index exceeds matrix dimensions.

i am new user of matlab, i want to get the number of zero crosses and the total energy of a audio wave, but when i do run this program it gives an error :

>>[ plot(blocks(1,1:len))
Index exceeds matrix dimensions.]

the code :

len = length(blocks);

n = sum(size(blocks)) - len;

min = n+1;

max = 0;

sumthreshtotal = len * sumthresh;

zerocrossthreshtotal = len * zerocrossthresh;

for i = 1:n

    currsum = sum(abs(blocks(i,1:len)));

    currzerocross = zerocross(blocks(i,1:len));

    if or((currsum > sumthreshtotal),(currzerocross > zerocrossthreshtotal))
      if i < min

        min = i;

      end

      if i > max;

        max = i;

      end

    end

end

what should i change in order to make it run ?

thank you in advance.

[Geoff Hayes]

Hi Mouhamed,

Your above code seems incomplete. Is this a function that returns something? Why is there a plot command at the first line? Is the plot causing the error?

Have you tried stepping through the code to determine where your error originates?

The error "Index exceeds matrix dimensions" typically means that the code is trying to access an element of the array or matrix that does not exist. For example,

x=zeros(3,4);  % a 3x4 matrix of zeros
x(3,5);        % will generate the error since the third row has only 
               % four columns

So you should consider all places in the code that attempts to access any array or matrix element(s). There appears to be only two or three.

What are the dimensions of the blocks variable? Judging by the code, it seems that you are expecting it to have more than one row. Is it two dimensional? You are using the local variable n to access the rows in blocks . Rather than setting n as

n = sum(size(blocks)) - len;  % summing all dimensions and subtracting 
                              % max dimension length (assumes 2D)

try and replace it with

n = size(blocks,1);  % get the first dimension (number rows) in blocks

Likewise, since you are assuming that len is the number of columns in blocks , then just do

len = size(blocks,2);  % get the number of columns

Since you use n and len as information concerning the rows and columns of blocks respectively, then just use the size command to get this information for you, rather than length which just returns the maximum size of any dimension.

Else there may be a problem with zerocross .

Geoff

[Huda Zulfiqar]

Index exceeds matrix dimensions.
Error in Green (line 10)
a_g = a( :, :, 2 );

When i run the below code it shows the error "index exceeds matrix dimensions"

can anyone plzz tell me my mistake in this code??

clc;
clear;
close;
% Read the image 
a=imread('mouse.png');
% Convert to grayscale incase it is color
a = rgb2gray(a);
a_g = a( :, :, 2 );
b=size(a_g);
a=double(a_g);
% Loop for Getting the Histogram of the image
hist1 = zeros(1,256);
for i=1:b(1)
    for j=1:b(2)
        for k=0:255
            if a(i,j)==k
                hist1(k+1)=hist1(k+1)+1;
            end
        end
    end
end
%Generating PDF out of histogram by diving by total no. of pixels
pdf=(1/(b(1)*b(2)))*hist1;
%Generating CDF out of PDF
cdf = zeros(1,256);
cdf(1)=pdf(1);
for i=2:256
    
    cdf(i)=cdf(i-1)+pdf(i);
end
cdf = round(255*cdf);
ep = zeros(b);
for i=1:b(1)                                        %loop tracing the rows of image
    for j=1:b(2)                                    %loop tracing thes columns of image
        t=(a(i,j)+1);                               %pixel values in image
        ep(i,j)=cdf(t);                             %Making the ouput image using cdf as the transformation function
    end                                             
end
% Loop for Getting the Histogram of the image
hist2 = zeros(1,256);
for i=1:b(1)
    for j=1:b(2)
        for k=0:255
            if ep(i,j)==k
                hist2(k+1)=hist2(k+1)+1;
            end
        end
    end
end
subplot(2,2,1);
imshow(uint8(a_g));
title('Original Image');
subplot(2,2,2);
imshow(uint8(ep));
title('Image after Histogram Equalization');
subplot(2,2,3);
stem(hist1);
title('Histogram of the Original Image');
subplot(2,2,4);
stem(hist2);
title('Histogram after Histogram Equalization of the Original Image');
suptitle(' The original green channel image along with image after histogram equalization with their respective histograms')

[Geoff Hayes]

Huda - in the code

% Convert to grayscale incase it is color
a = rgb2gray(a);
a_g = a( :, :, 2 );

when you call rg2gray, a will be a grayscale image with dimensions mxnx1 and so trying to access the green component will fail. You probably want to create a second variable for the grayscale image so that you don't lose the original

% Convert to grayscale incase it is color
aGrayScale = rgb2gray(a);
a_g = a( :, :, 2 );