Write a function called blur that blurs the input image. The function is to be called like this:

Write a function called blur that blurs the input image. The function is to be called like this:

output = blur(img,w);

where img, the input image is a two-dimensional matrix of grayscale pixel values between 0 and 255. Blurring is to be carried out by averaging the pixel values in the vicinity of every pixel. Specifically, the output pixel value is the mean of the pixels in a square submatrix of size 2w+1 where the given pixel sits in the center. For example, if w is 1, then we use a 3x3 matrix, that is, we average all the neighboring pixels of the given pixel and itself. Only use valid pixels when portions of the blurring matrix fall outside the image. For example, the blurred value corresponding to w = 1 at index (1,1) would be the mean of of elements (1,1), (1, 2), (2,1) and (2, 2). Both input img and output output are of type uint8.

You can download the test image here

Opens in new tab

to use in MATLAB.

Code to call your function

img = imread('vandy.png');

output = blur(img,2);

imshow(output);

Can anyone please tell me where I am going wrong with the following code for this question? The code doesnot blur the image and just shows me the image.

function output = blur(img,w)
B=double(img);
[row col] = size(B);
k=2*w+1;
for r=2:row-k
for c=2:col-k
     MeanPixelVal=0;
for r1=r:(r+k-1)
for c1=c:(c+k-1)
MeanPixelVal = MeanPixelVal + double(img(r1,c1));
end
end
MeanPixelVal = MeanPixelVal/(k*k);
blurimg(r,c) = uint8(MeanPixelVal);
end
end
subplot(1,2,1); imshow(img); title('gray image, image intensity 0 - 255');
subplot(1,2,2); imshow(blurimg); str = strcat('blur image, w = ',num2str(w)); title(str);
output = uint8(B);
end

[Walter Roberson]

[Merged from https://www.mathworks.com/matlabcentral/answers/472573-write-a-function-called-blur-that-blurs-the-input-image ]

• Simple testVariable output has an incorrect value. Tested with a 5x5 uint8 matrix with all 255-s in the first and last rows and columns and zeros everywhere else and w = 1

• Assessment result: incorrectUsing image fileVariable output has an incorrect value. Tested with the vandy.png file and w = 1

Answer 1

[Image Analyst]

You never assign blurimg to B, so B remains the input image that you assigned it to way up at the top.

[Namarta Kapil]

I did as you said but its still showing me the same thing as before.

[Image Analyst]

Show me exeactly what you did. Attach the script.

[Namarta Kapil]

function output = blur(img,w)
blurimg=img;
B=blurimg;
[row col] = size(B);
k=2*w+1;
for r=2:row-k
for c=2:col-k
MeanPixelVal=0;
for r1=r:(r+k-1)
for c1=c:(c+k-1)
MeanPixelVal = MeanPixelVal + double(img(r1,c1));
end
end
MeanPixelVal = MeanPixelVal/(k*k);
blurimg(r,c) = uint8(MeanPixelVal);
end
end
subplot(1,2,1); imshow(img); title('gray image, image intensity 0 - 255');
subplot(1,2,2); imshow(blurimg); str = strcat('blur image, w = ',num2str(w)); title(str);
output = uint8(B);
end

[Walter Roberson]

Where is B(1,1) accessed?

[Namarta Kapil]

NVM this code is not correct for this excercise. I was not supposed to use the imshow function.

[Walter Roberson]

imshow() has nothing to do with where you are access B(1,1) .

r starts from 2. r1 starts from r and so has a minimum of 2. You access img(r1,c1) so you never access img(1, anything) . Therefore you cannot possibly be bluring correctly for the first w+1 rows.

Answer 2

[Rohit Patil]

function output = blur(img,w)
blurimg=img;
B=blurimg;
[row col] = size(B);
k=2*w+1;
for r=2:row-k
for c=2:col-k
MeanPixelVal=0;
for r1=r:(r+k-1)
for c1=c:(c+k-1)
MeanPixelVal = MeanPixelVal + double(img(r1,c1));
end
end
MeanPixelVal = MeanPixelVal/(k*k);
blurimg(r,c) = uint8(MeanPixelVal);
end
end
subplot(1,2,1); imshow(img); title('gray image, image intensity 0 - 255');
subplot(1,2,2); imshow(blurimg); str = strcat('blur image, w = ',num2str(w)); title(str);
output = uint8(B);
en

d

[Neha Prajapati]

This code is not working

[Image Analyst]

The d should be attached to the en so the last line should be "end".

end

[Sana Hafeez]

@Rohit Patil This code is not working

problem in line 19

please help me...

I am tired Now....

[Image Analyst]

Sana, attach your code, or use my attached code, or use the built-in imfilter() function.