How do I use IMFILTER to high pass filter an image?

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Sonoma Rich
Sonoma Rich 2011-8-5
评论： DGM 2022-4-27
How can I high pass filter an image (A) using IMFILTER(A,H)? What must the filter matrix (H) be to perform a high pass filter?

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Ashish Uthama
Ashish Uthama 2011-8-5
This tutorial might help.
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Image Analyst
Image Analyst 2011-8-6
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
imtool close all; % Close all imtool figures.
clear; % Erase all existing variables.
workspace; % Make sure the workspace panel is showing.
fontSize = 20;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
fullFileName = fullfile(folder, baseFileName);
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
% Didn't find it there. Check the search path for it.
fullFileName = baseFileName; % No path this time.
if ~exist(fullFileName, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image. numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Position', get(0,'Screensize'));
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')
% Filter 1
kernel1 = -1 * ones(3)/9;
kernel1(2,2) = 8/9
% Filter the image. Need to cast to single so it can be floating point
% which allows the image to have negative values.
filteredImage = imfilter(single(grayImage), kernel1);
% Display the image.
subplot(2, 2, 2);
imshow(filteredImage, []);
title('Filtered Image', 'FontSize', fontSize);
% Filter 2
kernel2 = [-1 -2 -1; -2 12 -2; -1 -2 -1]/16;
% Filter the image. Need to cast to single so it can be floating point
% which allows the image to have negative values.
filteredImage = imfilter(single(grayImage), kernel2);
% Display the image.
subplot(2, 2, 3);
imshow(filteredImage, []);
title('Filtered Image', 'FontSize', fontSize);
Tony
Tony 2011-8-9
A typical high-pass (or high emphasize filter) would be an unsharp mask.
H = fspecial('unsharp');
Pramod Bhat
Pramod Bhat 2011-8-25
Simple averaging your image can fulfill your need if u are not particular with the pass band.

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