i want to replace 2 pixels in the matrix by using this function between two pixels throw me this error

for k=1:ch2
    for i=1:r2
        for j=1:c2
            if New_im(i,j,k) >New_im(i+3,j,k)
                New_im(i+1,j,k)=New_im(round((((New_im(i,j,k) - New_im(i+3,j+3,k))/fact)*2) + New_im(i,j,k)),j,k) ;
                New_im(i+2,j,k)=New_im(round((((New_im(i,j,k) - New_im(i+3,j+3,k))/fact)*1) + New_im(i,j,k)),j,k) ;
            end
           
        end
    end
end

error that throwd

Index in position 1 is invalid. Array indices must be positive integers or logical values.

[Image Analyst]

What is the value of i, i+2, and i+3 when it throws the error? Are any of them floating point (have fractional parts), zero, negative, or larger than the number of rows in the New_im array?

What are the values of ch2, r2, c2, and fact?

You can reply after you read this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

Answer 1

[Jan]

Use the debugger to examine the problem:

dbstop if error

Then run the code again. When Matlab stops in the failing line, check the locally used variables. I guess that this is the line:

New_im(i+1,j,k)=New_im(round((((New_im(i,j,k) - New_im(i+3,j+3,k))/fact)*2) + New_im(i,j,k)),j,k);

Then check in the command window:

i, j, k
New_im(i,j,k)
(((New_im(i, j, k) - New_im(i+3, j+3, k)) / fact) * 2
round((((New_im(i, j, k) - New_im(i+3, j+3, k)) / fact) * 2) + New_im(i,j,k))

Obviously the index is not a positive integer.

[Walter Roberson]

Note in particular that the result of the round() + New_img(i,j,k) is being used as a index into New_im

Answer 2

[Voss]

Is this what you mean to do?

for k=1:ch2
    for i=1:r2
        for j=1:c2
            if New_im(i,j,k) > New_im(i+3,j,k)
                diff_im = (New_im(i,j,k) - New_im(i+3,j+3,k))/fact;
                New_im(i+1,j,k) = round(diff_im*2 + New_im(i,j,k));
                New_im(i+2,j,k) = round(diff_im + New_im(i,j,k));
            end
        end
    end
end