Converting 3D matrix to 2D matrix image

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.

Answer 1

[Matt J]

See rgb2gray or im2gray.

[Kartikeya]

Actually i am getting 3d Matrix only even though changed to greycolour . I need to get 2d matrix

Name Size Bytes Class Attributes

I 225x225 50625 uint8

RGB 225x225x3 151875 uint8

a 225x225 405000 double

i 225x225x3 1215000 double

[Matt J]

We can't see what you did to produce these results. Please run the operations here in the forum from start to finish.

[Kartikeya]

RGB = imread('photo_2023-10-16_18-46-00.jpg');
I = rgb2gray(RGB);
imshow(I);

[Dyuman Joshi]

@Kartikeya, I is a 2D array, see below -

RGB = imread('photo_2023-10-16_18-46-00.jpg');
I = rgb2gray(RGB);
whos

  Name          Size                Bytes  Class    Attributes

  I           225x225               50625  uint8              
  RGB         225x225x3            151875  uint8              
  ans           1x54                  108  char               
  cmdout        1x33                   66  char               

imshow(I);

[Kartikeya]

Is it possible to get RGB 225x225x3 as 225x225x2 because 225 is row and columns and 3 is a 3d matrix i need code for If the image is grayscale, it will become a 2D matrix. If it contains color information, it will remain a 3D matrix in loop cycle.

[Dyuman Joshi]

No, you can't have RBG as 225x225x2.

"i need code for If the image is grayscale, it will become a 2D matrix. If it contains color information, it will remain a 3D matrix in loop cycle. "

You are misunderstanding. Grayscale images are by definition 2D matrices, and RGB images are by definition 3D matrices. You don't need to convert them.

[Kartikeya]

Thanks

[Kartikeya]

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

Answer 2

[Image Analyst]

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.

[Kartikeya]

Thanks for code its helpful for me

[Kartikeya]

@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]

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?