MATLAB: How to code the total pixels number and white pixels and black area pixels number

Image Processing Toolboxpixels

how to code the total pixels number and white pixels and black area pixels number. If I just need half image how to do that? I'm learner in matlab. thanks

[fname path]=uigetfile('*.png','select an image');
fname=strcat(path,fname);
im=imread(fname);
imshow(im);
numWhitePixels = sum(im(:));
numPixels = sum(im(:));

Best Answer

Try this:

[baseName, folder]=uigetfile('*.png','select an image');
fullFileName = fullfile(folder, baseName);
grayImage = imread(fullFileName);
% Get the dimensions of the image.  
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Use weighted sum of ALL channels to create a gray scale image.
  grayImage = rgb2gray(grayImage); 
  % ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
  % which in a typical snapshot will be the least noisy channel.
  % grayImage = grayImage(:, :, 2); % Take green channel.
end
% Display the image.
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', 20, 'Interpreter', 'None');
% Assuming grayImage is a binary image...
numWhitePixels = nnz(grayImage); % Sum of non-zero pixels.
numPixels = numel(grayImage);
numBlackPixels = numPixels - numWhitePixels

Related Solutions

MATLAB: Why do not white pixels equal black pixels

Both your assumptions and your code are wrong. The pixels are not exclusively black or white, because there are also many many gray pixels in that image:

>> I = imread('photo.jpg');
>> U = unique(I(:));
>> H = histc(I(:),U);
>> [uint32(U),H]
ans =
           0        6000
           1      234000
          54        1200
         253        1200
         254        1200
         255      236400

The first column shows the RGB value, and the second column shows how many occurrences of each value are in that image.

This is a good example of how beginners often have some belief about what code is doing. But they do not bother to actually check. Code does not care is in your head, nor what you imagine it to be doing. Your job is to check what it is actually doing. Just because you imagine that all pixels are exactly black or white does not mean that they are. And any code that made that assumption would be pretty awful code!

MATLAB: Masking some desired portion of an image

It definitely DOES work, but you need to make your mask in the range 0-1. Here's proof:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
fontSize = 20;
format compact;
% Read in a standard MATLAB color demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'peppers.png';
fullFileName = fullfile(folder, baseFileName);
% 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]); % Maximize figure.
mask = zeros(rows, columns, 'uint8');
mask(30:300, 50:150) = 1;
% Normalize to 0 - 1.
mask = mask / 255;
% Display the mask.

subplot(2, 2, 2);
imshow(mask, []);
title('Mask', 'FontSize', fontSize);
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask,class(rgbImage)));
% Display the mask.
subplot(2, 2, 3);
imshow(maskedRgbImage, []);
title('MaskedImage', 'FontSize', fontSize);

Best Answer

Related Solutions

MATLAB: Why do not white pixels equal black pixels

MATLAB: Masking some desired portion of an image

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