how to set threshold value for comparing images in matlab?

Question

AFFY 2015-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/178534-how-to-set-threshold-value-for-comparing-images-in-matlab

评论： Image Analyst 2023-3-30

how do I compare one image for example Z with multiple images in a folder and find out the one which matches closely to the image Z.

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Answer 1

Image Analyst 2015-2-15

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You develop an algorithm. That's about all I can say, given the (lack of) information you've provided. Please read this and provide more info.

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AFFY 2015-2-16

thanks a lot. Is there any way of interfacing a scanner to MATLAB?? So that the images are directly read from the scanner without human intervention??

Image Analyst 2015-2-16

Not that I'm aware of. You might be able to use a twain interface or java robot but I can't help you there.

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Answer 2

Pranav Shukla 2023-3-28

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编辑：DGM 2023-3-28

在 MATLAB Online 中打开

close all; 
clc;
path='C:\Users\Vinayak Shukla\Documents\MATLAB\MATLAB PROJECTS\MASTER THESIS FOLDER 2023\happy15_encrpted4.bmp';
list=dir([path, '*.jpg']);
img=imread('C:\Users\Vinayak Shukla\Documents\MATLAB\MATLAB PROJECTS\MASTER THESIS FOLDER 2023\happy15_encrpted4.bmp');
%image to compare with X1=rgb2ind(img,16);
forx=1:length(list); 
images{x}=imread([path, list(x).name]);
X2=rgb2ind(images{x},16); 
c=corr2(X1,X2);
figure(x); 
subplot(1,2,1),imshow(images{x}), xlabel(['Image ',num2str(x)]); 
subplot(1,2,2),imshow(img);
if c==1 
    xlabel('The images are same.');  
else
    xlabel('The images are not same');
end 

This is the error i am getting

Unrecognized function or variable 'x'.

Error in pranav17 (line 8)

images{x}=imread([path, list(x).name]);

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DGM 2023-3-28

编辑：DGM 2023-3-28

在 MATLAB Online 中打开

Here. This is cleaned up.

I don't know why you were converting things to indexed color and then trying to compare the index arrays. The mapping is not continuous, so there would be no point in finding the correlation coefficients. They'd either be equal or not; coefficients less than 1 would be meaningless as a measure of image similarity. I simply omitted that.

If you need the images for later, preallocate by creating a cell array. If you don't need them outside the loop, don't bother storing them.

% read from a set of IPT test images
basepath = fullfile(matlabroot,'toolbox/images/imdata');
filenameexpr = 'AT3*.tif';
matchingfiles = dir(fullfile(basepath,filenameexpr));
% reference image
% doing rgb2ind() on images and then comparing them does not
% yield a comparison of the actual image values.
% i'm just going to grab the first image in the sequence
Xref = imread(fullfile(matchingfiles(1).folder,matchingfiles(1).name));
numimages = numel(matchingfiles);
imagestack = cell(numimages,1); % preallocate
for k = 1:numimages
    % read a file to test
    thispath = fullfile(matchingfiles(k).folder,matchingfiles(k).name);
    Xtest = imread(thispath);
    
    % store it if necessary
    % if you don't need to keep them for later, don't bother
    imagestack{k} = Xtest;
    
    % test it somehow (corr2, immse, isequal)
    c = immse(Xref,Xtest); % mean-square error
    
    % generate a pile of figures
    figure(k); 
    subplot(1,2,1),imshow(Xtest), xlabel(['Image ',num2str(k)]); 
    subplot(1,2,2),imshow(Xref);
    if c==0 % if error is zero
        xlabel('The images are same.');  
    else
        xlabel('The images are not same');
    end 
end

Pranav Shukla 2023-3-30

编辑：DGM 2023-3-30

在 MATLAB Online 中打开

basepath = fullfile(matlabroot,'toolbox/images/imdata');
filenameexpr = '(C:\Users\Vinayak Shukla\Documents\MATLAB\MATLAB PROJECTS\MASTER THESIS FOLDER 2023\happy15_encrpted4.bmp)';
matchingfiles = dir(fullfile(basepath,filenameexpr));
Xref = imread(fullfile(matchingfiles().folder,matchingfiles().name));
numimages = numel(matchingfiles);
imagestack = cell(numimages,1); % preallocate
for k = 1:numimages
    thispath = fullfile(matchingfiles(k).folder,matchingfiles(k).name);
    Xtest = imread(thispath);
    
    % store it if necessary
    % if you don't need to keep them for later, don't bother
    imagestack{k} = Xtest;
    
    % test it somehow (corr2, immse, isequal)
    c = immse(Xref,Xtest); % mean-square error
    
    % generate a pile of figures
    figure(k); 
    subplot(1,2,1),imshow(Xtest), xlabel(['Image ',num2str(k)]); 
    subplot(1,2,2),imshow(Xref);
    if c==0 % if error is zero
        xlabel('The images are same.');  
    else
        xlabel('The images are not same');
    end 
end