HOW TO APPLY A MEAN FILTER FOR 3x3
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I NEED TO APPLY THE 3x3 MEAN FILTER TO THE GRAY SCALE IMAGE. PLS SEND ME THE CODE FOR THAT
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Wayne King
2012-9-27
How about just:
h = 1/3*ones(3,1);
H = h*h';
% im be your image
imfilt = filter2(H,im);
6 个评论
Walter Roberson
2023-2-10
Check class() of the input image and class() of the output image. I suspect that class of the output is double and that you would get what you want if you uint8() that.
DGM
2023-2-10
What is the class and scale of the input and output? The rendering of an image depends on an assumption of where white and black are. Floating-point images are expected to be unit-scale (i.e. 0-1). If you're using the above code, then it will be uint8-scale (0-255)
% this is a uint8 image
im = imread('cameraman.tif');
% create filter
h = 1/3*ones(3,1);
H = h*h';
% the output of this will be class 'double', but scaled as if uint8
imfilt = filter2(H,im);
% cast it to a class appropriate for its scale
imfilt = uint8(imfilt);
% display it
imshow(imfilt)
See also:
更多回答(5 个)
Image Analyst
2012-9-27
filteredImage = conv2(single(grayscaleImage), ones(3)/9);
7 个评论
Ridho Liwardana
2022-3-23
It's depend of matrix that you wanna use as filter, if it's a 3x3 matrix, the value is 1/(3x3) -> 1/9.
Image Analyst
2022-3-23
@SP The reason you divide by windowWidth^2 (1/9 in this case) is because if you don't, the filtering is the sum of the filter window times the image to be filtered. So if the image were all 255 under the filter, you'd get an output value of 9*255 instead of 255. So the image would be 9 times as bright. To ensure that the filtered image lies in the same intensity range as the original image, you need to divide the filter values by windowWidth^2.
If you didn't have a uniform filter (like here where they are all 1's) you'd have to divide by the sum of the kernel:
% Divide unnormalized kernel by the sum of the values in it.
% This will ensure the output image has the same intensity range as the original.
kernel = kernel / sum(kernel(:));
outputImage = imfilter(grayImage, kernel);
Actually, that is the most general approach which will work for any filter.
Mohamed Batran
2015-7-11
thank you for your reply simple but helped a lot for customizing the filter i want
0 个评论
Geetha raja
2018-8-19
I NEED TO APPLY THE bilateral FILTER TO THE GRAY SCALE IMAGE for denoising. PLS SEND ME THE CODE FOR THAT
1 个评论
Image Analyst
2018-8-19
Geetha, there is a part of the web site called "File Exchange". You can look there for community-contributed programs: Search for bilateral filter
Jahid Hasan
2022-4-19
Sorry to ask here, how to write mean and median filter without using a in-built function? What are the way to do it? Any help or code syntax. Thank you
4 个评论
Walter Roberson
2022-4-19
Potential reference implementation. Not tested.
sum_of_elements = 0;
index_of_element = 0;
while true
index_of_element = index_of_element + 1;
try
sum_of_elements = sum_of_elements + YourVector(index_of_element);
catch ME
break; %we ran off the end of the array
end
end
number_of_elements = index_of_element - 1; %loop over-counts by 1
mean_of_YourVector = sum_of_elements ./ number_of_elements;
sorted_vector = bogosort(YourVector, number_of_elements);
index_of_element = 0;
while true
index_of_element = index_of_element + 1;
if index_of_element + index_of_element == number_of_elements
median_of_YourVector = YourVector(index_of_element);
break
elseif index_of_element + index_of_element + 1 == number_of_elements
median_of_YourVector = (YourVector(index_of_element) + YourVector(index_of_element+1)) / 2;
break
end
end
function sortedVector = bogosort(vectorToSort, number_of_elements)
%this is a legitimate sort
while true
neworder = randperm(number_of_elements);
sortedVector = vectorToSort(neworder);
index_of_element = 0;
while true
index_of_element = index_of_element + 1;
if index_of_element >= number_of_elements
%we got to the end of the list without detecting out-of-order
return;
end
if YourVector(index_of_element) > YourVector(index_of_element+1)
%detected something out of order, try again with a new order
break
end
end
end
end
DGM
2022-4-19
As far as sliding filter/convolution examples go, here are some links. I'm sure there are others. These are just the ones I have in my notes.
general sliding/moving window filter base
same thing only with a gaussian mean setup
basic mean filter example
basic 2D convolution build (full size)
basic 2D convolution build (same size)
另请参阅
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