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How do I threshold the image automatically based on its energy content?
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Say my threshold is taking in those components that constitute about 75% of energy of image and making the remaining as zero.How do I do that?
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Image Analyst
le 14 Sep 2018
D_coder, try this:
clc; % Clear the command window.
clearvars;
close all; % Close all figures (except those of imtool.)
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
grayImage = imread('cameraman.tif');
subplot(2, 2, 1);
imshow(grayImage);
title('Original Image', 'FontSize', fontSize);
sortedGrayLevels = double(sort(grayImage(:), 'descend'));
% Sum up the energy from most energetic to least energy.
percentage = cumsum(sortedGrayLevels);
percentage = percentage / percentage(end);
subplot(2, 2, 2);
plot(percentage, 'b-', 'LineWidth', 2);
grid on;
title('Cumulative Distribution Function', 'FontSize', fontSize);
% Find the brighter 75%
% Find the gray level where 75 percent is
index75 = find(percentage >= 0.75, 1, 'first')
grayLevel75 = grayImage(index75)
% threshold the most energy 75%
binaryImage = grayImage > grayLevel75;
subplot(2, 2, 3);
imshow(binaryImage);
title('Brighter 75%', 'FontSize', fontSize);
% Find the darker 75%
% Find the gray level where 75 percent is
index75 = find(percentage >= 0.25, 1, 'first')
grayLevel25 = grayImage(index75)
% threshold the most energy 75%
binaryImage25 = grayImage < grayLevel25;
subplot(2, 2, 4);
imshow(binaryImage25);
title('Darker 75%', 'FontSize', fontSize);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/195663/image.png)
Each binary image will contain 75% of the energy. It just depends if you wanted to start with the darker pixels and work brighter, or start with the brightest pixels and work darker.
2 commentaires
Christie John Jacob
le 3 Fév 2020
Modifié(e) : Image Analyst
le 3 Fév 2020
While using this code matlab displayed an error message that there is error in imshow function
' Error using images.internal.imageDisplayValidateParams>validateCData (line 119)
If input is logical (binary), it must be two-dimensional.
Error in images.internal.imageDisplayValidateParams (line 27)
common_args.CData = validateCData(common_args.CData,image_type);
Error in images.internal.imageDisplayParseInputs (line 78)
common_args = images.internal.imageDisplayValidateParams(common_args);
Error in imshow (line 245)
images.internal.imageDisplayParseInputs({'Parent','Border','Reduce'},preparsed_varargin{:});
Error in gray (line 27)
imshow(binaryImage) '
Why is this coming ?
Image Analyst
le 3 Fév 2020
I just copied and ran the code and it ran beautifully. You must have altered it somehow. Maybe you read in a true color RGB image instead of a gray scale image to fix that, put this right after the call to imread():
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Use weighted sum of ALL channels to create a gray scale image.
grayImage = rgb2gray(grayImage);
% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
% which in a typical snapshot will be the least noisy channel.
% grayImage = grayImage(:, :, 2); % Take green channel.
end
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