How can i crop the image based on white pixel value

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Stephen john 2022-7-31

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评论： Image Analyst 2022-8-2

Hello Everyone, I hope you are doing well. i have the following image I want to crop the image based on min and maximum value. as you can see i have the pixel value at 348 , 343 and 338 , so he minimum value is 338 and maximum value is 348 so i want to crop the image and so the values lies in the image.

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Image Analyst 2022-7-31

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Not sure I see anything from that image. Anyway if you crop the image based on the image's min and max value, you will of course end up with the entire image - all pixels.

If the image has values below some other "min" value you specify you can do

mask = grayImage >= minValue & grayImage <= maxValue;
[r, c] = find(mask);
row1 = min(r);
row2 = max(r);
col1 = min(c);
col2 = max(c);
croppedImage = grayImage(row1:row2, col1:col2);

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Image Analyst 2022-8-1

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Try this:

% Demo by Image Analyst
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
markerSize = 40;
%--------------------------------------------------------------------------------------------------------
% READ IN IMAGE
folder = pwd;
baseFileName = 'image1.png';
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
    % The file doesn't exist -- didn't find it there in that folder.
    % Check the entire search path (other folders) for the file by stripping off the folder.
    fullFileNameOnSearchPath = baseFileName; % No path this time.
    if ~exist(fullFileNameOnSearchPath, 'file')
        % Still didn't find it.  Alert user.
        errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
        uiwait(warndlg(errorMessage));
        return;
    end
end
rgbImage = imread(fullFileName);
% 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(rgbImage)
if numberOfColorChannels > 1
    % It's not really gray scale like we expected - it's color.
    fprintf('It is not really gray scale like we expected - it is color\n');
    % Extract the blue channel.
    grayImage = rgbImage(:, :, 1);
else
    grayImage = rgbImage;
end
%--------------------------------------------------------------------------------------------------------
% Display the gray scale image.
subplot(2, 1, 1);
imshow(grayImage);
impixelinfo;
axis('on', 'image');
title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
drawnow;
mask0 = grayImage ~= 0;
minValue = min(grayImage(mask0))
maxValue = max(grayImage(mask0))
mask = grayImage >= minValue & grayImage <= maxValue;
[r, c] = find(mask);
row1 = min(r);
row2 = max(r);
col1 = min(c);
col2 = max(c);
croppedImage = grayImage(row1:row2, col1:col2);
%--------------------------------------------------------------------------------------------------------
% Display the image.
subplot(2, 1, 2);
imshow(croppedImage);
impixelinfo;
axis('on', 'image');
title('Cropped Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
drawnow;

Stephen john 2022-8-2

@Image Analyst Your code work good. If i want to crop 5 pixel above and 5 pixel below the Values how can i do that?

Image Analyst 2022-8-2

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croppedImage = grayImage((row1 - 5) : (row2 + 5), col1 : col2);

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DGM 2022-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/1771555-how-can-i-crop-the-image-based-on-white-pixel-value#answer_1018690

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pepcircmask.png

Assuming that the image is 2D, this is one way

A = imread('pepcircmask.png');

imshow(A)

% find the first and last row containing nonzero elements

nzrows = any(A,2);

idx1 = find(nzrows,1,'first');

idx2 = find(nzrows,1,'last');

% extract that region

A = A(idx1:idx2,:);

imshow(A)

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Stephen john 2022-8-2

@Image Analyst Okay i think i can't deliver it properly . the code you share work Okay, I want to use the same code and crop the image 5 pixel above the one white pixel value and 5 pixel below the 5 pixel value so i can get some black background too.