Not getting channel 1 in an Face images even though in Grey-colour

originalImage = imread('greyface2.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 = 264

columns = 191

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

Answer 1

[Harsha Vardhan]

Hi,

I understand that you want to check if an image is a gray scale image.

In many cases, gray colored images are stored as RGB images. When the R, G and B values of a pixel are either equal or very close to each other, that pixel gets the appearance of grayscale. In such cases, it must not inferred that the image is a gray scale image. Such an image can still contain 3 channels of R, G and B.

When you load such an image in MATLAB using imread, it will still read it as a 3-channel RGB image, because that's how the image is stored. That's why you're seeing numberOfColorChannels as 3.

To understand further, please execute the below code and observe the output.

originalImage(1,1,:)

  1×1×3 uint8 array

ans(:,:,1) =

   197


ans(:,:,2) =

   198


ans(:,:,3) =

   200

It can be seen from the above output that the first pixel - originalImage(1,1,:) has 3 channels associated with it. And the values of each channel are very close to each other. This gives an impression of greyscale inspite of having 3 channels.

If you want to ensure you're working with a true single-channel grayscale image in MATLAB, you can convert it using:

grayImage = im2gray(originalImage);  

This answer has more information about the values returned by the 'size' function in the context of images - https://www.mathworks.com/matlabcentral/answers/81089-finding-the-dimensions-of-an-image#answer_939490

Hope this helps in resolving your query!

[Kartikeya]

@Harsha Vardhan Can you please share the full code from starting to ending then i can understand in easy manner.

[Kartikeya]

@Harsha Vardhan But i want that its was gray in colour and if it is in colour image automically it should convert and print channel 1. If you have any code please share

[Harsha Vardhan]

@Kartikeya The image you attached 'greyface2.jpg' is a RGB image and not a greyscale image. As explained in the abvove answer, since the R,G and B values are close to each other at each pixel, the final mixed color appears grey.

Please explain what do you want to achieve with your code so that I can help you further.

[Kartikeya]

@Harsha Vardhan I need to achieve its in gray colour and print of 2d matrix. If you have any grey image please share i want run with my code.

[Harsha Vardhan]

@Kartikeya

As explaine here, https://www.mathworks.com/help/matlab/ref/im2gray.html#mw_b4fbc85d-d8ff-40b0-97c3-f00ec7fc2429

You can use 'im2gray' function to convert both RGB images as well as grey scale images to grey scale images without any verification.

originalImage = imread('greyface2.jpg');
grayImage = im2gray(originalImage);  

[Harsha Vardhan]

@Kartikeya

originalImage = imread('greyface2.jpg');
grayImage = im2gray(originalImage);  

'grayImage' contains a 2d matrix.

[Kartikeya]

@Harsha Vardhan

Thanks for Helping . I have done till this and now suppose it is R,G,B print its colour in channel 1, 2, 3 etc. And below i am sharing an image can you please tell how to identify whether it is 2d matrix or not.

Code :-

originalImage = imread('ali.jpg');

grayImage = rgb2gray(originalImage);

imshow(grayImage)

[Harsha Vardhan]

@Kartikeya

In the screenshot you attached, the colunm 'size' displays the size of the matrix. The 'grayImage'has 365x265 in the 'size' column. It means it can be identified as a 2-dimensional matrix since it has only rows X columns.

[Kartikeya]

@Harsha Vardhan Thanks If any doubts again i will ping in comment