use a character for loop in matlab

Question

I want to use a character in for loop but I can't because I'm using ginput function and it's possible to first and end pixel in for loop changed by every mouse click I cant use an exact pixel it's my error when run my code.

Subscript indices must either be real positive integers or logicals.

A=imread('peppers.png');
C=imshow(A);
F=rgb2gray(A);
figure,imshow(F)
B=ginput(4)
a=min(B);
b=max(B);
a1=a(1)
a2=a(2)
b1=b(1)-a(1)
b2=b(2)-a(2)
for i=a1:a1+b1
    for j=a2:a2+b2
       F(j,i)=0;
    end
end
figure,imshow(F)

I recommend to read the MATLAB documentation about Indexing. It can save you a lot of work. F(a1:a1+b1,a2:a2+b2)=0 fully replaces the two loops and is faster. — Daniel
– Daniel, Commented Feb 15, 2016 at 11:46

Daniel · Accepted Answer · 2016-02-15 12:40:57Z

1

The values you get from input are slightly off the full integer. Use B-round(B) and you see the error.

To fix it, use round

B=round(ginput(4))

The error message was really curious

Attempted to access F(142,162); index must be a positive integer or logical.

edited Feb 15, 2016 at 12:40

answered Feb 15, 2016 at 11:38

Daniel

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1 Comment

Daniel Over a year ago

@StewieGriffin: The comment you deleted was right, you can still break it simply clicking the area outside the image.

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