RGB images are 3-D(i.e 3 , 2-D array for R,G,B ), can we extract these array seperatly?

I want to convert the 3-D image array into 1-D array, so if i got R,G & B array seperatly then these can be converted into 2-D array easily.. so how to get these 3 (R,G,B) array??

Answer 1

[Wayne King]

You just select each "page" of the matrix.

im = imread('ngc6543a.jpg');
Rim = im(:,:,1);
Gim = im(:,:,2);
Bim = im(:,:,3);

[priyanka]

When i am using imtool() function and checking the pixel information,pixel value is not matched with the pixel value which is obtained by redChannel = rgbImage(:, :, 1); greenChannel = rgbImage(:, :, 2); blueChannel = rgbImage(:, :, 3);

[Image Analyst]

To solve that we will need you to attach a screenshot of imtool with your cursor showing one RGB and x,y set of values, and your original image and code

Something like

rgbImage = imread('peppers.png');
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
imtool(rgbImage);
x = 10;
y = 300;
hold on;
plot(x, y, 'r+', 'MarkerSize', 30);
fprintf('RGB(%d, %d) = (%d, %d, %d)\n',...
redChannel(y, x), greenChannel(y, x), blueChannel(y, x));

Are you sure you didn't confuse (x,y) with row,column)? Very very common mistake. Remember (x,y) is (column, row), NOT (row, column) like you need to program into your code.

[priyanka]

Thank you,, its working .:)

[MAHMOOD QADIR]

Thank you very much

Answer 2

[Image Analyst]

Extract each color channel

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);

as shown in my attached demo that takes RGB histograms of every image in your folder.

Screenshot:

[Yassine Zaafouri]

is this working for tif Image with a sensor alignment 'grbg' ?

[Image Analyst]

Yes, if you're looking at the demosaiced (normal) image. If you're looking at the "raw" (non-demosaiced) image, then you'll have 4 color channels and you can just take the histogram of 4 instead of 3 color channels. I'm not sure where the demosaicing takes place in your system - while it's saving out to a tiff, or if it's expecting you to do that yourself later. If it demosaiced it before saving, like most cameras, then when imread reads it back in, it should be a 3 color channel RGB image, not a 4 channel image.

[Yassine Zaafouri]

So i have a raw Image from a camera (1280*980 unit16 grbg) , then i extracted from it just a smaller Image ( 644*640 ) because i do not need the rest . Then i Worte with this new Matrix a new image and i saved it with the format tif because i think it is easier to work with when you compare it to .raw . Then when i call your function with this image it doesn't work that's why i called the function demosaic and then wrote a new image . After that i called your function with this image but the results are strange . There is my code and i hope you understand the Problem .

if true
  new = im_raw(y1:y4, x1:x4 );
imwrite(uint16(new),'xyz.tif','compression','none')
test=double(imread('.\xyz.tif'))
figure; imshow(test,[160 4000])
title ('tif image ')
test1=imread('.\xyz.tif')
J = demosaic(test1,'grbg');
imwrite(uint16(J),'abc.tif')

end

[Image Analyst]

Why is im_raw not 3D? It should be 1280 rows by 980 columns by 4 color channels, shouldn't it? How did you get im_raw read in, and what is its layout? Why is it only 2D?

[Yassine Zaafouri]

it is an image sensor for automotive aand i took a monochrome image . But i think when i do that, the rgb informations are stored with the raw image, shouldn't it? so when i want to extract the rgb layers it should work.

if true
 Sensor info:
//  Width          = 1280
//  Height         = 980
//  Image Format   = Bayer 12
//  Subformat      = GRBG
//  Sensor output  = 12 bits per pixel
//
//  .RAW file info:
//  stored as      = 16 bits unsigned short
end 
and that's how i read the image 

if true
  fid1 = fopen('capture0003.raw');
helpinterx = fread(fid1,'uint16');
helpinter=reshape(helpinterx,1280,964);
helpinter = helpinter';
im_raw=helpinter;
end

[Image Analyst]

That doesn't look right. If the image is 980 by 1280 by 4 color channels, and you've read in all the data, then your reshape would not work since your new desired size does not contain all the pixels. I suggest you start your own discussion thread (rather than keep bugging priyanka), and read this and attach your actual image.

[Jeykishan]

Thank you for the code. Very informative and usefl for me.

Answer 3

[priyanka]

When i am using imtool() function and checking the pixel information,pixel value is not matched with the pixel value which is obtained by redChannel = rgbImage(:, :, 1); greenChannel = rgbImage(:, :, 2); blueChannel = rgbImage(:, :, 3);

[Image Analyst]

Attach your image. There's a good possibility you're cheking the value using the x,y from the cursor in imtool as redChannel(x,y), which would be incorrect. Remember y is row, not x, so it needs to be redChannel(y, x), NOT redChannel(x, y);