Converting 3D matrix to 2D matrix image

Question

Kartikeya 2023-10-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2034269-converting-3d-matrix-to-2d-matrix-image

评论： Image Analyst 2023-10-20

I am working with a JPEG image, if it results in a 3D matrix (225x225x3), you can convert it to 2D. If the image is grayscale, it will become a 2D matrix. If it contains color information, it will remain a 3D matrix. Could someone please share the code or steps to be followed.

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Answer 1

Matt J 2023-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/2034269-converting-3d-matrix-to-2d-matrix-image#answer_1334304

See rgb2gray or im2gray.

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Kartikeya 2023-10-16

Thanks

Kartikeya 2023-10-16

May i know what is meant by A, I, RGB in the names

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Answer 2

Image Analyst 2023-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/2034269-converting-3d-matrix-to-2d-matrix-image#answer_1334324

在 MATLAB Online 中打开

Try these two code snippets. The first one gives you a grayscale image, regardless of what's in the file.

originalImage = imread(fullFileName);
% To get a 2-D grayscale image from the file, converting from RGB
% to gray scale if it's not already grayscale.
% 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(originalImage)
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 red channel.
    grayImage = originalImage(:, :, 1); % 2 for green, 3 for blue.
    % OR ALTERNATIVELY use the rgb2gray() function to do a weighted average of all 3 color channels.
    grayImage = rgb2gray(originalImage);
else
    % It's already gray scale.  Just put it into our grayImage variable.
    grayImage = originalImage;
end

The second one gives you an RGB image regardless of what's in the file.

originalImage = imread(fullFileName);
% To get a 2-D grayscale image from the file, converting from RGB
% to gray scale if it's not already grayscale.
% 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(originalImage)
if numberOfColorChannels > 1
    % It's already RGB.  Just put it into our rgbImage variable.
    rgbImage = originalImage;
else
    % It's not really RGB like we expected - it's grayscale (or indexed).  We'll assume it's grayscale here.
    fprintf('It is not really RGB like we expected - it is grayscale.\n');
    % Concatenate the gray scale image to be all 3 color channels.
    rgbImage = cat(3, originalImage, originalImage, originalImage);
end

If it's indexed, we'll need some additional code to use ind2rgb to apply the colormap.

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Kartikeya 2023-10-18

在 MATLAB Online 中打开

greyface1.jpg

@Image Analyst Not getting channel 1 in an Face images even though in Grey-colour based on your code. Can you please help me. I am storing every image in jpeg format.

originalImage = imread('greyface1.jpg');
% To get a 2-D grayscale image from the file, converting from RGB
% to gray scale if it's not already grayscale.
% 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(originalImage)
rows = 183
columns = 275
numberOfColorChannels = 3
if numberOfColorChannels > 1
    % It's already RGB.  Just put it into our rgbImage variable.
    rgbImage = originalImage;
else
    % It's not really RGB like we expected - it's grayscale (or indexed).  We'll assume it's grayscale here.
    fprintf('It is not really RGB like we expected - it is grayscale.\n');
    % Concatenate the gray scale image to be all 3 color channels.
    rgbImage = cat(3, originalImage, originalImage, originalImage);
end

Image Analyst 2023-10-20

Not sure what you want. You're using the code snippet to make an image an RGB image, but your image is already an RGB image. See? It says numberOfColorChannels = 3 so that means it's already color, and so there is nothing really to do to make it color. I just put it into another, more secriptively named variable. So why should you get gray scale?

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