Extract RGB values of multiple images

Hello,

I have 300 images that I would like to extract the rgb values of each image individually. How can I do that?

Thanks

Answer 1

[Image Analyst]

Use imread to get the RGB values of each image

for k = 1 : 300
    filename = whatever
    rgbValues = imread(filename);
end

[Danah Abdulghani A Aljishi]

thanks for the help. But this does not give the (R), the (G), and the (B) seperately for each file individually.

I know how to manually do that for each file, but I can't figure out how to do it for a batch of files at once.

this is the code I ran:

myFolder = '......./Pictures/Coarse - 1';

filePattern = fullfile(myFolder, '*.jpg');

theFiles = dir(filePattern);

for k = 1 : length(theFiles)

baseFileName = theFiles(k).name;

fullFileName = fullfile(myFolder, baseFileName);

rgbValues2 = imread(fullFileName);

end

Thanks.

[DGM]

Use imsplit() or basic array indexing to separate the color channels. Doing this in the loop is no different than doing it with a single file. Any further complications are a consequence of what you intend to do with the data. Since that's something that hasn't been revealed, there is no way to give you a bespoke tool that does everything you want. It'll be up to you to apply the concepts to the multiple-file workflow, whatever that is.

inpict = imread('peppers.png');

% split image using imsplit()
[R G B] = imsplit(inpict);

% or split image using basic array indexing
R = inpict(:,:,1);
G = inpict(:,:,2);
B = inpict(:,:,3);

Note that both examples presume that the input is always RGB. It'll be up to you to make sure all inputs are RGB, or otherwise to decide what should happen when the inputs aren't RGB.

[Danah Abdulghani A Aljishi]

Thank you both for the help! it worked and I managed to do it like this:

myFolder = '......./Pictures/Fine - 1';
filePattern = fullfile(myFolder, '*.jpg'); 
theFiles = dir(filePattern);
n = length(theFiles);
R = cell(n,1);
G = cell(n,1);
B = cell(n,1);
for k = 1 : n
    baseFileName = theFiles(k).name;
    fullFileName = fullfile(myFolder, baseFileName);
    inpict = imread(fullFileName);
    R{k} = inpict(:,:,1) ; % Red
    G{k} = inpict(:,:,2) ; % Green
    B{k} = inpict(:,:,3) ; % Blue
end

[Image Analyst]

I see no reason for storing all the color channels for every images. You may run out of memory if you have too many images. Why are you storing them? Do you need them later (in a different loop of function) for some reason and don't want to read them in again and would rather keep them all stored in memory? If you need to do something with the R, G, and B matrices, then just operate on them there in that single loop. If you really think you need them stored forever (for the rest of your program) then explain why - I'm willing to be convinced if you show me proof it's needed.

[Danah Abdulghani A Aljishi]

I need to extract them from matlab and use them in another program.

I'm not a matlab user so if there's a better way to extract them, do share.

[DGM]

I don't know what other program has problems separating color channels, but there are a lot of things I don't know. If all you truly need to do is split the images and save the image channels independently, then I don't see why you can't do that in the loop. You'll just have to use imwrite() to write each channel to an appropriate filename and directory.

I will point out that it would be a generally bad idea to use JPG as the output file format. Use PNG if data integrity is of any concern.

[Image Analyst]

Then you'll need to use imwrite instead of stuffing them all into a cell array, which your other program won't understand.

myFolder = '......./Pictures/Fine - 1';
filePattern = fullfile(myFolder, '*.jpg'); 
theFiles = dir(filePattern);
n = length(theFiles);
R = cell(n,1);
G = cell(n,1);
B = cell(n,1);
for k = 1 : n
    baseFileName = theFiles(k).name;
    fullFileName = fullfile(myFolder, baseFileName);
    rgbImage = imread(fullFileName);
    [r, g, b] = imsplit(rgbImage);
    % Get file parts
    [folder, baseFileNameNoExt, ext] = fileparts(fullFileName);
    % Save images to disk for the other program that needs them.
    % Save red channel.
    outputBaseFileName = sprintf('%s_R.png', baseFileNameNoExt);
    outputFullFileName = fullfile(folder, outputBaseFileName);
    imwrite(r, outputFullFileName);
    % Save green channel.
    outputBaseFileName = sprintf('%s_G.png', baseFileNameNoExt);
    outputFullFileName = fullfile(folder, outputBaseFileName);
    imwrite(g, outputFullFileName);
    % Save blue channel.
    outputBaseFileName = sprintf('%s_R.png', baseFileNameNoExt);
    outputFullFileName = fullfile(folder, outputBaseFileName);
    imwrite(b, outputFullFileName);
end