MATLAB: Imhist() is not generating histogram image of image

histogramImage Processing Toolboximhist

i have an RGB image and i am trying to generate histogram from the intensity image of the RGB. but my code is not generating histogram. please let me know how to solve

Pic = 'violet.bmp';
s1 = imread(Pic);
I1 = rgb2gray(s1);
imhist(I1);
imshow(I1);
drawnow();

this code only generatig till rgb2gray(), it is not generating imhist() part.

Best Answer

imhist(), as you called it, will display the histogram only. It will not return the histogram bin values. However, you immediately cover it up with the image so that the histogram can no longer be shown. Try this:

baseFileName = 'violet.bmp';
fullFileName = fullfile(pwd, baseFileName);
if exist(fullFileName)
  rgbImage = imread(fullFileName);
  grayImage= rgb2gray(rgbImage);
  [pixelCounts grayLevels] = imhist(grayImage, 256);
  bar(grayLevels, pixelCounts);
  xlim([0 255]);
  uiwait(msgbox('Click OK to see the image'));
  imshow(grayImage);
else
  warningMessage = sprintf('Error: file not found\n%s', fullFileName);
  uiwait(warndlg(warningMessage));
end

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Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 25;
% 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.
  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
referenceGrayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(referenceGrayImage);
if numberOfColorBands > 1
  % It's not really gray scale like we expected - it's color.
  % Convert it to gray scale by taking only the green channel.
  referenceGrayImage = referenceGrayImage(:, :, 2); % Take green channel.
end
% Display the original gray scale image.

subplot(2, 2, 1);
imshow(referenceGrayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
% Let's compute and display the histogram.
[pixelCount, grayLevels] = imhist(referenceGrayImage);
subplot(2, 2, 2);
bar(grayLevels, pixelCount);
grid on;
title('Histogram of original image', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
srcFiles = dir(fullfile(folder, '*.jpg')); %directory of the source folder
Im1 = im2double(referenceGrayImage); % Calculate the Normalized Histogram
hn1 = imhist(referenceGrayImage)./numel(referenceGrayImage);
for i = 1 : length(srcFiles)      % determins how many images are there in the folder,
  filename = fullfile(folder,srcFiles(i).name)
  thisImage = imread(filename);
  % Display the original gray scale image.
  subplot(2, 2, 3);
  imshow(thisImage);
  title(filename, 'FontSize', fontSize);
  drawnow;
  Im2=rgb2gray(thisImage);
  Im2 = im2double(Im2);
  hn2 = imhist(Im2)./numel(Im2);
  
  % Calculate the histogram error

  f(i) = sum((hn1 - hn2).^2);% Calculate the histogram error
  f(i) %display the result to console  
  
  promptMessage = sprintf('f=%f\nDo you want to Continue processing,\nor Cancel to abort processing?',f(i));
  titleBarCaption = 'Continue?';
  button = questdlg(promptMessage, titleBarCaption, 'Continue', 'Cancel', 'Continue');
  if strcmpi(button, 'Cancel')
    break;
  end
end

MATLAB: IMAGE 3D into 2D

[indI, cmapI] = rgb2ind(I);
imhist(indI, cmapI)

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