Horizontal average on Image

Given that the mask is hor = 0 0 0, 1 1 1, 0 0 0

I have to apply to my image. Afterwards, find the sum and divide by 3.

My code is:

clear;    % Clear the workspace
A = imread('Nature.jpg');
I = imrotate(A,90,'bilinear','loose');
grey = 0.21*I(:,:,1)+0.72*I(:,:,2)+0.07*I(:,:,3);
Grey = double(grey);

HorMask = [0 0 0;1 1 1;0 0 0];
[r,c] = size(Grey);
OUT = zeros(r-3,c-3);

for i = 1:(r-3)
    for j = 1:(c-3)
        GreySquare = Grey(i:(i+2),j:(j+2));
        res = HorMask.*GreySquare;
        Divide = res./3;
        OUT(i,j) = sum(Divide);
    end
end

figure()
imshow(OUT);

However, I am not able to divide by 3. with error message:

Subscripted assignment dimension mismatch.
Error in HorizontalAverage (line 16)
        OUT(i,j) = sum(Divide);

[Jan]

"I am not able" does not explain, what the problem is. Do you get an error message? If so, please post it completely. It is much easier to solve a problem than to guess, what the problem is.

Answer 1

[Andrei Bobrov]

A = imread('Nature.jpg');
I = imrotate(A,90,'bilinear','loose');
grey = 0.21*I(:,:,1)+0.72*I(:,:,2)+0.07*I(:,:,3); 
Grey = double(grey);
OUT = conv2(Grey,[1,1,1]/3,'same'); % or OUT = filter2([1,1,1]/3,Grey);

[Edina Lee]

I do not want to use the in-build function. Is there a way?

[Andrei Bobrov]

Hm! Homework?

[m,n] = size(Grey);
g = [zeros(m,1),Grey,zeros(m,1)];
ii = reshape(1:numel(g),[m, n + 2]);
OUT = mean(g(bsxfun(@plus,ii(:,1:end-2),reshape(m*(0:2),1,1,[]))),3);

[Edina Lee]

There is a error, the dimension do not match. do I need to change to double for the mean and reshape?

[Image Analyst]

If Andrei's new answer of not using built-in functions satisfies your definition of not using built-in functions, then please mark it as accepted to give him reputation points. Otherwise see this link.

http://www.mathworks.com/matlabcentral/answers/38787-what-can-be-programmed-without-any-built-in-functions

[Andrei Bobrov]

Thank you Image Analyst!

Hi Edina! I'm fixed my first comment.

[Edina Lee]

there is still an error and it shows:

Error using sum
Trailing string input must be 'double','native', or 'default'.

Error in mean (line 82)
    y = sum(x,dim,flag)/size(x,dim);

Error in Untitled2 (line 10)
OUT = mean(g(bsxfun(@plus,ii(:,1:end-2),reshape(m*(0:2),1,1,[]))),3,'omitnan');

[Andrei Bobrov]

Again fixed.