MATLAB: How to iteratively append elements to an array

arrayimage processingMATLAB

I = imread(chart_image);
R = I(:,:,1);
G = I(:,:,2);
B = I(:,:,3);
N= zeros(24,3);
final_chart =zeros (24,3);
Vals = [175 175;  425 175; 650 175; 925 175;
        175 420; 425 420; 650 420; 925 420;
        175 670; 425 670; 650 670 ; 925 670 ;
        175 925;  425 925; 650 925; 925 925;
        175 1170; 425 1170; 650 1170; 925 1170;
        175 1425; 425 1425 ; 650 1425 ; 925 1425];
 for i = 1:24
    N(i)=[R(Vals(i,1),Vals(i,2)) G(Vals(i,1),Vals(i,2)) B(Vals(i,1),Vals(i,2))];   
    final_chart % the variable I want to modify to be able to store the vales of all N as it iterates over the 24 values in Vals into a single 24x3 matrix
  end
hello, I wanted to add the value of each N to a final array called final_chart, but I keep getting error "Unable to perform assignment because the left and right sides have a different number of elements.", I've tried other ways to append but for some reason I keep failing all of those. Can someone help me understand where I'm going wrong and help me fix my code. Thank you.

Best Answer

If I understood what you're trying to do, there's no need for the loop:
I = imread(chart_image);
R = I(:,:,1);
G = I(:,:,2);
B = I(:,:,3);
Vals = [175 175;  425 175; 650 175; 925 175;
        175 420; 425 420; 650 420; 925 420;
        175 670; 425 670; 650 670 ; 925 670 ;
        175 925;  425 925; 650 925; 925 925;
        175 1170; 425 1170; 650 1170; 925 1170;
        175 1425; 425 1425 ; 650 1425 ; 925 1425];
locations = sub2ind(size(R), Vals(:, 1), Vals(:, 2));
N = [R(locations), G(locations), B(locations)];
You don't even need to separate the image into colour planes:
I = imread(chart_image);
[width, height, ~] = size(I);
Vals = [175 175;  425 175; 650 175; 925 175;
        175 420; 425 420; 650 420; 925 420;
        175 670; 425 670; 650 670 ; 925 670 ;
        175 925;  425 925; 650 925; 925 925;
        175 1170; 425 1170; 650 1170; 925 1170;
        175 1425; 425 1425 ; 650 1425 ; 925 1425];
locations = sub2ind([width, height], Vals(:, 1), Vals(:, 2));
N = I(locations + (0:2) * width * height);
Related Question