MATLAB: Counting the number of black pixels in an image

image processingImage Processing Toolboxmask

Hello, I need help counting the number of black pixels in an image that was just taken through a camera. My current program is able to take an image and then convert the image into a black and white image based on the colors in the first image. I need to count the amount of black pixels in the processed image that was just taken that only contains black and white pixels. If it helps, here is my code so far (P.S. This includes some code that I have commented out to get the program working to this point):

clc
clear
clear all
images= []
webcamlist()
cam= webcam(1)
preview(cam)
pause(2);
images= snapshot(cam)
imshow(images)
r_channel= images(:,:,1);
g_channel= images(:,:,2);
b_channel= images(:,:,3);
images(:,:,1) =0;
images(:,:,3) = 0;
image(images);
mask= g_channel > 100, b_channel > 800, r_channel < 800, b_channel < 0, r_channel < 0;
imshow(mask)
 gr_ratio = double(g_channel)./double(r_channel);
 gb_ratio = double(g_channel)./double(b_channel);
 rb_ratio = double(r_channel)./double(b_channel);
 
% gr_ratio(isnan(g_ratio))=0;
% grayImage = rgb2gray(image);
% binaryImage = grayImage > 20;
% binaryImage = bwareaopen(binaryImage, 50);
% binaryImage = imfill(binaryImage, 'holes');
% grayImage(~binaryImage) = 0;
falseMatrix= zeros(7,7);
targetMatrix= ones(7,7);
checkMatrix= ones(7,7);
if targetMatrix == checkMatrix
%     cam = camStop;
    return
end

Best Answer

If "mask" is the image you want to count black pixels in, you can either do it like this:

numBlackPixels = numel(mask) - nnz(mask)

or like this:

numBlackPixels = sum(~mask(:))

Related Solutions

MATLAB: Segment Image based on Color pixels.

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = 'A1.jpg';
folder = pwd;
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
%=======================================================================================
% Read in demo image.
rgbImage = imread(fullFileName);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(rgbImage)
% Display image.
subplot(2, 2, 1);
imshow(rgbImage, []);
impixelinfo;
axis on;
caption = sprintf('Original Color Image\n%s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% 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')
drawnow;
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% get a mask for the red line.
mask = redChannel > greenChannel;
% Display the image.


subplot(2, 2, 2);
imshow(mask);
caption = sprintf('Color Segmentation Mask Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
axis('on', 'image');
drawnow;
% fill holes.
mask = imfill(mask, 'holes');
% Take the largest blob only.
mask = bwareafilt(mask, 1);
% Shrink two layers of pixels to come inside the red lines.
mask = imerode(mask, true(5));
% Display the image.
subplot(2, 2, 3);
imshow(mask);
title('Final Mask', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
axis('on', 'image');
% Get a masked image.
% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));
% Display the image.
subplot(2, 2, 4);
imshow(maskedRgbImage);
title('Masked RGB Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
axis('on', 'image');
% Tell user the answer.
message = sprintf('Done!');
uiwait(helpdlg(message));

MATLAB: Unable to perform assignment because the size of the left side is 122-by-123 and the size of the right side is 146-by-158.

The variable filtered_img is existing before. Either use

clear filtered_img

before assigning a new value. Or better store the code in a function, such that the workspace is not polluted by old variables. Or create the variable completely instead of this indexing method:

filtered_img = cat(3, medfilt2(R_channel), medfilt2(G_channel), medfilt2(B_channel));

This overwrites a formerly existing variable.

Best Answer

Related Solutions

MATLAB: Segment Image based on Color pixels.

MATLAB: Unable to perform assignment because the size of the left side is 122-by-123 and the size of the right side is 146-by-158.

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