Converting 3D matrix to 2D matrix image

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Kartikeya
Kartikeya 2023-10-16
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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Matt J
Matt J 2023-10-16
See rgb2gray or im2gray.
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Kartikeya
Kartikeya 2023-10-16
May i know what is meant by A, I, RGB in the names

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Image Analyst
Image Analyst 2023-10-16
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
Kartikeya 2023-10-18
Ran in:
@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
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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