MATLAB: How to count the number of pixels from an image for specifies colors

counting number of pixels of particular color

I have used the code stated below.

if true
  % code

imread color.jpg
load color.jpg
redChannel = color(:, :, 1);
greenChannel = color(:, :, 2);
blueChannel = color(:, :, 3);
whitePixels = redChannel    == 255 & ...
            greenChannel  == 255 & ...
            blueChannel   == 255; 
count = sum(whitePixels(:));
Red1Pixels = redChannel    == 255 & ...
            greenChannel  == 166 & ...
            blueChannel   == 166;
count = sum(Red1Pixels(:));
Red2Pixels = redChannel    == 254 & ...
            greenChannel  == 85 & ...
            blueChannel   == 82; 
count = sum(Red2Pixels(:))
Blue1Pixels = redChannel    == 179 & ...
            greenChannel  == 169 & ...
            blueChannel   == 250; 
count = sum(Blue1Pixels(:))
Blue2Pixels = redChannel    == 255 & ...
            greenChannel  == 255 & ...
            blueChannel   == 255; 
count = sum(Blue2Pixels(:))
end

and I am getting error as below.

if true
  % code
Index exceeds matrix dimensions.

Error in Try_03_07_2018 (line 17) greenChannel = color(:, :, 2); and Try_03_07_2018 is the file name.

Kindly help me out of this.

Regards,

Jotheeshwar V

Best Answer

Neither

imread color.jpg

nor

load color.jpg

import the pixels of the image to th variable color. Use this instead:

color = imread('color.jpg');

By the way: I'd expect load color.jpg to show an error already. So are you sure that your code run at all?

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MATLAB: How to convert specific pixel value to pseudocolor

Is one of these what you are looking for? Walter's right about the ambiguity so I picked a couple of possibilities (grayscale changing the image and not using a colormap, and RGB thresholding each channel individually) and programmed up a demo for you. If neither case is what you want, then you must clarify. Don't worry about the length, just copy, paste, and run, then study the code later.

clc;  % Clear command window.
clear;  % Delete all variables.
close all;  % Close all figure windows except those created by imtool.
imtool close all;  % Close all figure windows created by imtool.
workspace;  % Make sure the workspace panel is showing.
fontSize = 16;
% Read in a standard MATLAB color demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'football.jpg';
% Get the full filename, with path prepended.

fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % 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.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
rgbImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows columns numberOfColorBands] = size(rgbImage);
% Display the original color image.
subplot(2, 2, 1);
imshow(rgbImage, []);
title('Original Color Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Threshold each color channel to get pixels darker than 40.

redMask = redChannel < 40;
greenMask = greenChannel < 40;
blueMask = blueChannel < 40;
% Apply the mask

redChannel(redMask) = 255;
greenChannel(greenMask) = 0;
blueChannel(blueMask) = 0;
% Recombine into RGB image.

rgbImage = cat(3, redChannel, greenChannel, blueChannel);
% Display

subplot(2, 2, 2);
imshow(rgbImage, []);
title('Masked Color Image', 'FontSize', fontSize);
promptMessage = sprintf('Now we will do it for a gray scale image?');
titleBarCaption = 'Continue with gray scale example?';
button = questdlg(promptMessage, titleBarCaption, 'Continue', 'Cancel', 'Continue');
if strcmp(button, 'Cancel')
  return;
end
% 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);
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
subplot(2, 2, 3);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Get red, green, and blue channels.
redChannel = grayImage;
greenChannel = grayImage;
blueChannel = grayImage;
% Threshold each color channel to get pixels darker than 40.
mask = grayImage < 40;
% Apply the mask
redChannel(mask) = 255;
greenChannel(mask) = 0;
blueChannel(mask) = 0;
% Recombine into RGB image.
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
% Display
subplot(2, 2, 4);
imshow(rgbImage, []);
title('Masked Color Image', 'FontSize', fontSize);

MATLAB: How to make a crop image with a white color result

Do you want white space or not any space over cropped area. Refer this. Since you have not pasted the original image, I am taking your attached image as input.

A=imread('24.jpg');
subplot(1,2,1)
imshow(A)
subplot(1,2,2)
[m,n]=size(A);
imshow(A(round(m/2)-100:round(m/2)+100,round(m/2)-100:round(m/2)+100))

Best Answer

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MATLAB: How to convert specific pixel value to pseudocolor

MATLAB: How to make a crop image with a white color result

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