MATLAB: Difference between hist and imhist

histImage Processing Toolboximhist

Hi,

I have a fundamental question about the hist and imhist and an explanation will be great as I am a bit lost.

I am running this script:

I = imread('pout.tif');
figure;
x=imhist(I)
imhist(I)
figure(2);
hist(x)

and when I compare the two histograms they do not look alike, why?

How can I save the imhist data so that the hist will show the same plot?

Thanks

Best Answer

For a gray scale image imhist() will give 256 bins. hist() only gives 10 by default. But you did not use hist() to take the histogram of the image - the badly-named "I". You used it to take a histogram of the histogram counts, x - a pretty weird/strange thing to do.

Related Solutions

MATLAB: IMAGE 3D into 2D

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

MATLAB: 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.

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.

Best Answer

Related Solutions

MATLAB: IMAGE 3D into 2D

MATLAB: 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.

Related Question