How can i get a RGB values from a picture?

Hi,

My goal is to get the RGB values of the image taken with the webcam and I need the matlab code to accomplish this purpose. I am a new matlab user, please help me.

Best regards.

Answer 1

[Walter Roberson]

See https://www.mathworks.com/help/supportpkg/usbwebcams/ug/acquire-images-from-webcams.html on how to work with webcams.

Once you have done the snapshot(), then just index into the resulting array to get the RGB values. For example,

img(183, 17, :)

would extract the R, G, and B components (in that order) of row 183 column 17 of the image.

[caner kaya]

Thank you, but do you have a sample code with all the algorithms.I can be very basic at this level, sory, but I am very happy if you can help.

[Walter Roberson]

The link above shows code that should get you at least as far as being able to get an image from the camera.

[caner kaya]

thank you so much, To summarize, I will associate the photo taken with the webcam with matlab using the code above and then use an appropriate function to get the RGB value of this photo.

[Walter Roberson]

Yes.

[caner kaya]

oke, thank you and lastly, can you give me some more information on getting RGB values, please. I ask many questions, forgive me:)

[Tiago Batanete Marques]

Walter, I was browsing through this question because it seemed similar to one I have. The solution your provided works fine if I want to know the RGB values of specific pixels of my photo. However, what if I want to store all the RGB values of all the pixels of the photo in one array, how can I do it? And what type of array I might get? Thank you in advance.

[Image Analyst]

In Walter's example, img is the storage of ALL the RGB values of ALL the pixels of the photo in one array. The array is usually of class uint8 (unsigned 8 bit integer).

[Tiago Batanete Marques]

But assuming that I have this:

camera = webcam;

img = snapshot(camera);

The variable 'img' is an 720x1280x3 uint8 array (in my case), right? This array represents the image itself, am I right? I know that this array contains information about the color, but my goal is to create a different variable, like 'color_matrix' in which I have an array with just the color information, which I can use later in function such as pointCloud(). I don't know if my question makes sense... Thanks in advance.

[Image Analyst]

For example:

img = imread('peppers.png');
colorcloud(img)

[Walter Roberson]

color_matrix = reshape(img, [], 3);

There would be one row for each of the (row times columns) of the original matrix. For example,

[R,C] = ndgrid(1:size(img,1), 1:size(img,2));
X = C(:); Y = R(:);
color_matrix = reshape(img, [], 3);
pointsize = 10;
scatter3(X, Y, pointsize, color_matrix);

[Tiago Batanete Marques]

Thanks for both answers. I tried to do that and now I have a different problem. The reshape function did in fact reshape and extract the RGB values. However, I ended up with a 2-D array. To use this "color_array" in the pointCloud function, this "color_array" needs to be tridimensional, that is, with the same dimension as the picture used in the same pointCloud function. I tried to do a little research but I found nothing. Could you help me, please? I don't even know if this is possible in Matlab.

[Image Analyst]

What do you want represented along each axis? LIke R along , G along Y and B along Z?

Like this:

rgbImage = double(imread('peppers.png'));
[r, g, b] = imsplit(rgbImage);
xyz = [r(:), g(:), b(:)];
ptCloud = pointCloud(xyz);
pcshow(ptCloud)

Looks pretty much like what you get from colorcloud():

[Walter Roberson]

Your color data can be either 2D or 3D

numFaces = 600;
[x,y,z] = sphere(numFaces);
xyz2d = [x(:), y(:), z(:)];
xyz3d = cat(3,x,y,z);
img = imresize(imread('flamingos.jpg'), [numFaces+1, numFaces+1]);
color_matrix_2d = reshape(img, [], 3);
color_matrix_3d = img;
pcshow(xyz2d, color_matrix_2d); title('data arranged as 2d')

pcshow(xyz3d, color_matrix_3d); title('data arranged as 3d')

Answer 2

[Chad Greene]

Hi Caner,

The imread function will read any image and give you the RGB values like this:

A = imread('myimage.jpg');

Then the red layer is the first slice of A, blue is the second slice, and green is the third:

R = A(:,:,1); 
G = A(:,:,2); 
B = A(:,:,3);

If you need the RGB values of a specific pixel, say, row 22, column 50, it would be:

[R(22,50) G(22,50) B(22,50)]

If you're not sure what the row and column numbers are of the pixel you want, display the image with the image function, then use ginput to click around and get the coordinates you want:

image(A) 
[col,row] = ginput

[Walter Roberson]

Note: imread() applies to image files, not to getting images from webcams, for which you should use snap(). However, the information about color slices is relevant.

[Shri.s]

This solution does not shows the RGB values?

[DGM]

This does show the RGB values at a specific pixel.

% an image
A = imread('peppers.png');

% split the channels
R = A(:,:,1); 
G = A(:,:,2); 
B = A(:,:,3);

% address each channel to find the color at (22,50)
[R(22,50) G(22,50) B(22,50)]

ans = 1×3

61 35 65

% of course, this is the same as
permute(A(22,50,:),[1 3 2])

ans = 1×3

61 35 65

Answer 3

[Image Analyst]

To build on what the others said, you should look at impixelinfo() which is a function that puts a status bar on your figure that gives you the (x,y) location and RGB values as you mouse over the displayed image.

There is also a function called impixel() that gives you the RGB value but I never use it.

[caner kaya]

Are there any files or links I can get information about these functions?

[Walter Roberson]

https://www.mathworks.com/help/images/ref/impixelinfo.html

[caner kaya]

thank you, As far as I can tell, I can get RGB values of the image using only this function, I am sure? Do you have a code for this algorithm,I am very basic at this level, sory!

[Walter Roberson]

No, there are other ways to get RGB values from an image. But which RGB values do you want to get?

imshow(YourImage);
datacursormode('on')

Now left click on the image and notice that a box comes up showing your location and the pixels. If you left click somewhere else, it will show the values for that location. If you left click and hold the mouse and move, it will update the information as you move.

These are useful if you want to manually examine an image, but if want compute something with the image, such as average brightness, then you would not use these at all: you would access array locations like Chad and I showed.

[caner kaya]

I need to find R G B values between 0 and 255 for a picture for example if the picture pure red then R=255, G=0, B=0, I should get these values

[caner kaya]

I also have a problem, the RGB values I get are not affected by the environment. I mean I should get the * same* values even if I'm in the dark or the bright environment with the using the webcam

Answer 4

[Bryan Benedict Ordas]

Hello Guys!

I am also in need of help on getting the RGB values in a multiple images. I was able to know also that you can pick a certain coordinates using your mouse to select the pixel you wanted to obtain the RGB Values. What if I wanted to use this function for multiple pictures? is there a way on looping this activity? (selecting pixels and getting the RGB Values of Multiple Pictures).

My purpose was to gather data of a certain object for neural networks.

Thanks!!!

[Bryan Benedict Ordas]

I'm new on using Matlab so please be easy on me... hehe, thanks!

[Image Analyst]

See the FAQ for code samples on how to read in multiple images and get their RGB values.

FAQ : Process a sequence of files