Problem with to calculated the prewitt

Dear colleague I have a problem to calculate a parameter of feature of a image. This parameter is calculated by means the sum of intensity pixels of orginal images where the filter prewitt is one between the total pixel that filter prewitt is equal a one for each regions of my images.

I try in matlab the following sentences:

PW=edge(L,'prewitt'); %L is the label matrix with all regions of my images

for k=1:num  %num is the number of regions in L, In this case 47

ind=find(L==k);

li=length(ind);

for i=1:li

if(PW(ind)~=0)

cont(i)=cont(i)+1;

sum(i)=y2(ind);

end

end

end

but these sentences give a error. What is the problem? Could someone help me?, please.

Thank you vey much in advance

[Walter Roberson]

Related question by the same author: http://www.mathworks.com/matlabcentral/answers/20464-problem-with-generate-exterior-border-of-regions

Answer 1

[Walter Roberson]

"ind" will usually be a vector, and indeed you loop "i" over the length of that vector. But you access PW(ind) and since ind is generally a vector, PW(ind) will generally be a vector. Your test

if(PW(ind)~=0)

is thus an "if" applied to a vector. MATLAB does define the meaning of that: it defines the test as being true only if all of values in the vector are non-zero (true) . Supposing that does happen, then you increment cont(i) and then extract y2(ind)... which is generally going to be a vector result. You then try to store that vector in the single element sum(i) which is going to fail. And then you loop around and for the next value of "i", you make exactly the same test.

Inside the loop, your references to ind should probably be references to ind(i)

Note: using "sum" as a variable name usually results in program bugs, as "sum" is the name of an important and commonly used MATLAB function.

[Cristina]

Do you say me that I change ind by ind(i)and the name sum?

If I change it, the sentences in Matlab are:

for k=1:num %num is the number of regions in L, In this case 47

ind=find(L==k);

li=length(ind);

for i=1:li

if(PW(ind(i))~=0)

cont(i)=cont(i)+1;

suma(i)=suma(i)+y2(ind(i));

end

end

end

But it give me a error "??? Undefined function or method 'suma' for input arguments of type 'double'" also the variable cont isn´t calculate. Cont after the this instruction has a one of value.

I believe that I don`t understand your answers. Could you explain it again, please?

Thank you very much

[Walter Roberson]

You did not initialize suma anywhere. Before the loop, put

cont = zeros(li,1);

suma = zeros(li,1);

[Walter Roberson]

All of your cont values will be either 0 or 1. You set up your code that way. I do not know what you are expecting cont to count, so I cannot offer any suggestions.