I am not sure how i can get histogram both the fig which i looked in are the same.. Anybody help me in completing the code.

clc;
close all;
clear all;
img=imread('C:\UsersDesktop\dipproj2\lena.bmp');
[p,q]=size(img)
k=1:0:256;
x= ones(1,256);

for k=1:0:256
        for i=1:size(p,1)
        for j=1:size(q,1)
            k=value(256,i)
           % if (img(i,j)==k)
              % x(k+1)=x(k+1)+1;
              x(k+1)=x(k+1)+1;
               end
            end
end
d=zeros(1,256);
d=x*(1/(p*q));
s=sum(k+1)
s(1)=d(1,1);

for i=2:256
    s(i)=s(i-1)+d(1,i);
end
y=ones(1,256);
u=y*256
%sk=255*s;
 z=floor(u);
 final=img;
for k=0:256
        for i=1:size(256,1)
        for j=1:size(256,1)
        if(img(i,j)==k)
        final(i,j)=z(1,k+1)+1;
        end
        end
        end
end
 figure(1),
 subplot(2,1,1),
 title('histogram'),
 imagesc(final),
 colormap(gray);
 subplot(2,1,2),
 imhist(final);
 figure(2),
 subplot(2,1,1),
 title('histogram1'), 
 imagesc(img),
 colormap(gray);
 subplot(2,1,2),
 imhist(img);

[Image Analyst]

What do you think this line will do:

for k=1:0:256

You have a step size of 0!!!!

Answer 1

[Image Analyst]

Why are you computing the histogram yourself??? You know, there is a function for that called imhist() in the Image Processing Toolbox. See this demo:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 22;

% Read in a standard MATLAB color demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'peppers.png';
% 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
% Read in the image from disk.
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);

% Get histograms for each color channel.
[pixelCountsR grayLevelsR] = imhist(redChannel, 256);
[pixelCountsG grayLevelsG] = imhist(greenChannel, 256);
[pixelCountsB grayLevelsB] = imhist(blueChannel, 256);

% Plot them
subplot(2, 2, 2);
bar(grayLevelsR, pixelCountsR, 'BarWidth', 1, 'FaceColor', 'r');
grid on;
title('Red Histogram', 'FontSize', fontSize);
subplot(2, 2, 3);
bar(grayLevelsG, pixelCountsG, 'BarWidth', 1, 'FaceColor', 'g');
grid on;
title('Green Histogram', 'FontSize', fontSize);
subplot(2, 2, 4);
bar(grayLevelsB, pixelCountsB, 'BarWidth', 1, 'FaceColor', 'b');
grid on;
title('Blue Histogram', 'FontSize', fontSize);

Regarding your code...What do you think this line will do:

for k=1:0:256

You have a step size of 0!!!! And in this line:

for k=0:256

what do you think will happen when k = 256 in this line:

final(i,j)=z(1,k+1)+1;

Normally you run from 0 to 255 (but not as indexes) or from 1 to 256, not from 0 to 256.

[sandeep]

I need to develop the code without the imhist function. please could you provide me another code for histogram equalization without using imhist function. Let me know if I change the step size and index, does the code works fine?

[Image Analyst]

It's easy enough for you to try. Just change 0 to 1 and run it.

[Image Analyst]

Well, because you at least gave a shot at it, I decided to correct the first part of the code. Hopefully you can get the last part where you apply the transform to the image to equalize it.

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 22;

% 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, 1);
imshow(grayImage, []);
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') 

% Compute the histogram
theHistogram= ones(1,256);
theHistogram = zeros(1,256);
for i=1:rows
  for j=1:columns
    % Get the gray level of this pixel
    grayLevel = grayImage(256,i);
    % Increment the histogram at that gray level.
    theHistogram(grayLevel+1) = theHistogram(grayLevel+1) + 1;
  end
end
% Plot the histogram as a bar chart.
subplot(2, 2, 2); 
bar(theHistogram);
grid on;
title('Histogram of original image', 'FontSize', fontSize);
xlim([0 256]); % Scale x axis manually.

% Compute the CDF of the histogram without using cumsum().
cdf(1)= theHistogram(1);
for k = 2 : 256
  cdf(k) = cdf(k - 1) + theHistogram(k);
end
% Plot CDF.
subplot(2, 2, 3); 
plot(cdf);
grid on;
title('CDF of original image', 'FontSize', fontSize);
xlim([0 256]); % Scale x axis manually.