How can I implement the nearest neighbor interpolation properly by myself?

Hello!

I really need help with my code to implement the nearest neighbor interpolation properly for RGGB image without using any available functions. The script looks as follows:

clear all close all clc

x = imread('Flowers.tiff'); x = double(x)/255; [m, n]=size(x);

r_mask=repmat([1, 0;0, 0],[m/2, n/2]); g_mask=repmat([0, 1;1, 0],[m/2, n/2]); b_mask=repmat([0, 0;0, 1],[m/2, n/2]);

r=x.*r_mask; g=x.*g_mask; b=x.*b_mask;

R=r; G=g; B=b;

for i=2:(m-1) for j=2:(n-1)

        %red canal R
        if (r(i-1,j)==0 && r(i+1,j)==0) && (r(i,j-1)==0 && r(i,j+1)==0)
            if r(i,j)==0
                R(i,j)=r(i,j);
            end
        elseif (r(i,j-1)==0 && r(i,j+1)==0) && (r(i-1,j)~=0 && r(i+1,j)~=0)
            R(i,j)=r(i,j);
        elseif (r(i-1,j)==0 && r(i+1,j)==0) && (r(i,j-1)~=0 && r(i,j+1)~=0)
            R(i,j)=r(i,j);
        end

         %green canal G
        if g(i,j)==0
           G(i,j)=g(i,j);
        end

        %blue canal B
        if (b(i-1,j)==0 && b(i+1,j)==0) && (b(i,j-1)==0 && b(i,j+1)==0)
            if b(i,j)==0
                B(i,j)=b(i,j);
            end
        elseif (b(i,j-1)==0 && b(i,j+1)==0) && (b(i-1,j)~=0 && b(i+1,j)~=0)
            B(i,j)=b(i,j);
        elseif (b(i-1,j)==0 && b(i+1,j)==0) && (b(i,j-1)~=0 && b(i,j+1)~=0)
            B(i,j)=b(i,j);
        end

    end
end

y(:,:,1)=R; y(:,:,2)=G; y(:,:,3)=B;

figure(), imshow(y);

The result:

What am I doing wrong?

[Image Analyst]

Attach the original raw image. Is your code one you saw somewhere for demosaicing?

[Aleksandra Kowalczuk]

Here is the raw image, originally it's .tiff but I had to convert into .jpg to attach:

The code is based on this example for bilinear interpolation:

[m, n]=size(x);

r_mask=repmat([1, 0;0, 0],[m/2, n/2]); g_mask=repmat([0, 1;1, 0],[m/2, n/2]); b_mask=repmat([0, 0;0, 1],[m/2, n/2]);

r=x.*r_mask; g=x.*g_mask; b=x.*b_mask;

R=r; G=g; B=b;

for i=2:(m-1) for j=2:(n-1)

        %red canal R
        if (r(i-1,j)==0 && r(i+1,j)==0) && (r(i,j-1)==0 && r(i,j+1)==0)
            if r(i,j)==0
                R(i,j)=(r(i-1,j-1)+r(i-1,j+1)+r(i+1,j-1)+r(i+1,j+1))/4;
            end
        elseif (r(i,j-1)==0 && r(i,j+1)==0) && (r(i-1,j)~=0 && r(i+1,j)~=0)
            R(i,j)=(r(i-1,j)+r(i+1,j))/2;
        elseif (r(i-1,j)==0 && r(i+1,j)==0) && (r(i,j-1)~=0 && r(i,j+1)~=0)
            R(i,j)=(r(i,j-1)+r(i,j+1))/2;
        end

         %green canal G
        if g(i,j)==0
           G(i,j)=(g(i,j-1)+g(i,j+1)+g(i+1,j)+g(i-1,j))/4;
        end

        %blue canal B
        if (b(i-1,j)==0 && b(i+1,j)==0) && (b(i,j-1)==0 && b(i,j+1)==0)
            if b(i,j)==0
                B(i,j)=(b(i-1,j-1)+b(i-1,j+1)+b(i+1,j-1)+b(i+1,j+1))/4;
            end
        elseif (b(i,j-1)==0 && b(i,j+1)==0) && (b(i-1,j)~=0 && b(i+1,j)~=0)
            B(i,j)=(b(i-1,j)+b(i+1,j))/2;
        elseif (b(i-1,j)==0 && b(i+1,j)==0) && (b(i,j-1)~=0 && b(i,j+1)~=0)
            B(i,j)=(b(i,j-1)+b(i,j+1))/2;
        end

    end
end

y(:,:,1)=R; y(:,:,2)=G; y(:,:,3)=B;

[Image Analyst]

That does not look like a raw RGGB mosaiced image. Why do you think it is?

[Aleksandra Kowalczuk]

I've got such result from Matlab function "demosaic".