MATLAB: How to extract RGB values of each pixel from an image

image processingMATLAB

I need to extract the RGB values of each pixel of a given image in a serial data format like R1:G1:B1, R2:G2:B2, R3:G3:B3… and so on.

Best Answer

Try this:

rgbImage = permute(rgbImage, [3,1,2])
serialValues = rgbImage(:)'

This will give you [r1,g1,b1, r2,g2,b2, r3,g3,b3, r4,g4,b4, ...] which is a row vector taken from the original RGB image in column major order.

Related Solutions

MATLAB: Sphere-based color slicing of image

Sucharita: Here, I've done 95% of it for you. If I do much more, then you'd just be turning in my answer as your own and I don't think your course rules allow that. You just need to replace the line that says "% code" with your own code and then display the output image after the loop is done.

% Demo to find color distances in RGB color space.  By Image Analyst, May 26, 2020.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
fprintf('Beginning to run %s.m ...\n', mfilename);
a1 = [134, 51, 143]
a2 = [131, 132, 4]
R0 = 30
%-----------------------------------------------------------------------------------------------------------------------------------
% Read in image.
folder = pwd;
baseFileName = 'image.jpeg';
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
	% The file doesn't exist -- didn't find it there in that folder.
	% Check the entire search path (other folders) for the file by stripping off the folder.
	fullFileNameOnSearchPath = baseFileName; % No path this time.
	if ~exist(fullFileNameOnSearchPath, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
rgbImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(rgbImage);
% Display the test image full size.
subplot(2, 2, 1);
imshow(rgbImage, []);
axis('on', 'image');
caption = sprintf('Reference Image : "%s"', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% Set up figure properties:
% Enlarge figure to full screen.
hFig1 = gcf;
hFig1.Units = 'Normalized';
hFig1.WindowState = 'maximized';
% 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.
hFig1.Name = 'Demo by Image Analyst';
[rows, columns, numberOfColorChannels] = size(rgbImage);
outputImage = zeros(rows, columns, numberOfColorChannels, class(rgbImage));
distanceImage = zeros(rows, columns);
for col = 1 : columns
	for row = 1 : rows
		thisR = double(rgbImage(row, col, 1));
		thisG = double(rgbImage(row, col, 2));
		thisB = double(rgbImage(row, col, 3));
		distanceImage(row, col) = sqrt((thisR - a1(1))^2 + (thisG - a1(2))^2 + (thisB - a1(3))^2); % or a2 for case ii
		if distanceImage(row, col) < R0
			% code...
		end
	end
end
maxDistance = max(distanceImage(:))
% Display the distance image.
subplot(2, 2, 2);
imshow(distanceImage, []);
axis('on', 'image');
caption = sprintf('Distance Image : "%s"', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
colorbar;
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Display the histogram of the distance image.
subplot(2, 2, 3);
histogram(distanceImage, 256);
grid on;
title('Histogram of Color Distances', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Gray Level', 'FontSize', fontSize, 'Interpreter', 'None');
ylabel('Count', 'FontSize', fontSize, 'Interpreter', 'None');
fprintf('Done running %s.m ...\n', mfilename);

MATLAB: Show a ROI over the original image

Henrique, see the demo code below that I wrote to produce this figure:

% Demo to have the user freehand draw an irregular shape over
% a gray scale image, have it convert that portion to a
% color RGB image defined by a colormap.
clc;  % Clear command window.
workspace;  % Make sure the workspace panel is showing.
fontSize = 16;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % File doesn't exist -- didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize);
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
message = sprintf('Left click and hold to begin drawing.\nSimply lift the mouse button to finish');
uiwait(msgbox(message));
hFH = imfreehand();
% Create a binary image ("mask") from the ROI object.
binaryImage = hFH.createMask();
xy = hFH.getPosition;
% Now make it smaller so we can show more images.
subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
drawnow;
title('Original Grayscale Image', 'FontSize', fontSize);
% Display the freehand mask.
subplot(2, 2, 2);
imshow(binaryImage);
axis on;
title('Binary mask of the region', 'FontSize', fontSize);
% Convert the grayscale image to RGB using the jet colormap.
rgbImage = ind2rgb(grayImage, jet(256));
% Scale and convert from double (in the 0-1 range) to uint8.
rgbImage = uint8(255*rgbImage);
% Display the RGB image.
subplot(2, 2, 3);
imshow(rgbImage);
axis on;
title('RGB Image from Jet Colormap', 'FontSize', fontSize);
% Extract the red, green, and blue channels from the color image.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Create a new color channel images for the output.
outputImageR = grayImage;
outputImageG = grayImage;
outputImageB = grayImage;
% Transfer the colored parts.
outputImageR(binaryImage) = redChannel(binaryImage);
outputImageG(binaryImage) = greenChannel(binaryImage);
outputImageB(binaryImage) = blueChannel(binaryImage);
% Convert into an RGB image
outputRGBImage = cat(3, outputImageR, outputImageG, outputImageB);
% Display the output RGB image.
subplot(2, 2, 4);
imshow(outputRGBImage);
axis on;
title('Output RGB Image', 'FontSize', fontSize);

Best Answer

Related Solutions

MATLAB: Sphere-based color slicing of image

MATLAB: Show a ROI over the original image

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