mse calculation for part of matrix

I have 2 matrix one is original image and second is the attacked image(512*512), now I should divide both of them to 31*31 blocks and then do DCT on these blocks, after that I consider 3 areas in each blocks ( suppose I divide block with 3 diagonal lines) and I should compute mse between DCT of original block and attacked block in each area? how can I do it?

Answer 1

[Image Analyst]

There is an immse() function.

[nadia]

OK, but I want to calculate mse of part of image for example a triangle part in top of image not whole of image. how can I do it?can I be clearly explain my purpose?

[Image Analyst]

Make a triangular mask using poly2mask

mask = poly2mask(x, y, rows, columns);

Then extract the pixel values in the mask

pixelValues1 = grayImage1(mask);
pixelValues2 = grayImage2(mask);

Then compute mse

numPixels = numel(pixelValues1);
squareErrors = sqrt((double(pixelValues1)-double(pixelValues2)).^2);
meanSquareError = sum(squareErrors) / numPixels;

[nadia]

that's good, thank you but if I want to calculate mse for middle part of image that extract 2 triangle from top and bottom of it? do you have any idea?like the image mse for each part.

[Image Analyst]

I told you in the first post. You do have the x and y coordinates of the triangle vertices, don't you? You have to have some way of specifying those triangles. If you don't have that, then why do you even care about the triangles? If you care about what the MSE there is, then you must care about the location of the triangles and therefore you must know the x,y coordinates.

[nadia]

I want to begin from index 1 to 14 in row and column to build above triangle but I do not know how to build poly2mask and make x and y? can you help me. the following image show which I want. can you guide me please?

[nadia]

OK, thank you very much I got it.