Find and plot the variation of R, G, and B values of the image

Looking for help on finding and plotting the values of R, G, and B of the attached image. Also to find pixel locations of the dark lines and the wavelength of the dark lines. I am new to MatLab and could use a little help. Thank you in advance.

[Walter Roberson]

No image was attached.

[Image Analyst]

What do you mean by wavelengths of the image you forgot to post? If you mean like color, wavelength in nanometers, then you can't get that from an RGB image. Lots of different single wavelengths, and continuous spectra (multiple groups of wavelengths), can produce the same RGB value.

[Walter Roberson]

I speculate the dark lines might be approximately regularly spaced and the spacing is to be calculated from the image. But we need further explanation.

[Garrett Nagy]

I thought I attached the image but I guess not sorry about that

[Walter Roberson]

Okay, but how would you like to "plot" the values of R, G, and B ?

[Garrett Nagy]

Each color on its own graph along the x direction. So the amount of color vs frequency probably

Answer 1

[Walter Roberson]

RGB = imread('YourImage.tif');
Red = RGB(:,:,1);
histogram(Red(:))

[Garrett Nagy]

i got the red to work but i cannot do the same thing for green or blue, i get an error that says index exceeds matrix dimensions. I tried to do BLUE = RGB(:,:,3) and GREEN = RGB(:,:,2) and came up with that error above.

[Walter Roberson]

It sounds like your tif might be pseudocolor

[img, map] = imread('YourImage.tif');

and check to see if img comes out 2 dimensional and map comes out non-empty. If so then you can use ind2rgb() to convert it to RGB

Answer 2

[Image Analyst]

Like I said before, you can't get wavelength from an RGB color. But if what you really want is a plot of the red signal, green signal, and blue signal as a function of distance along your x axis, then you can do that with this code:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 20;

% Open an image.
% Browse for the image file. 
[baseFileName, folder] = uigetfile('*.jpg', 'Specify a JPG image file'); 
fullImageFileName = fullfile(folder, baseFileName); 
if folder == 0
  return;
end

% Read in image into an array.
[rgbImage, storedColorMap] = imread(fullImageFileName); 
[rows, columns, numberOfColorBands] = size(rgbImage)
% If it's monochrome (indexed), convert it to color. 
if numberOfColorBands < 3
  uiwait(warndlg('It must be a color image'));
end

% Display the original image.
subplot(2, 1, 1);
imshow(rgbImage);
title('RGB Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis on;

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 

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

subplot(2, 1, 2);
% Plot the red signal
plot(redChannel(1, :), 'r', 'LineWidth', 2);
grid on;
hold on;
% Plot the green signal
plot(greenChannel(1, :), 'g', 'LineWidth', 2);
% Plot the blue signal
plot(blueChannel(1, :), 'b', 'LineWidth', 2);
title('Colors as function of distance along x axis', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Distance in Pixels', 'FontSize', fontSize');
ylabel('Gray Levels', 'FontSize', fontSize');
legend('Red', 'Green', 'Blue');

In addition, see the attached demo below, colormaps_plotted.m, where I do the same thing for any of the standard colormaps that you select.