looking for an alternative to ginput(n) to select a region on an image

Is there any built in function allowing to select a region on an image (interactively like in ginput) resulting in printing out corresponding coordinates?

Answer 1

[Image Analyst]

I think you're wanting impixelinfo(). Check out the documentation. It lets you mouse around over the image and a status text label updates the (x,y) location (or row,column - I don't remember) and the grayscale or RGB color.

[Alex]

thank you, If am not mistaken the impixelinfo() does allow to print out the results, also I need to select a region of an image using mouse not just one pixel. impixelinfo() gives info about just one pixel like in ginput().

[Image Analyst]

Define "print out". Do you actually mean to a paper printer?

Or perhaps you mean im2html, like discussed in Steve's blog:

http://blogs.mathworks.com/steve/2012/06/28/how-im2html-works/

Or perhaps you need imrect, imfreehand, imellipse, rbbox, or some other built-in function. Let me know - I have demos for all of those.

[Alex]

sorry for the slip of tongue. I need to select a region of an image using mouse and get coordinates of all pixels inside the region as a matrix. I studied docs and came to realize that all of the above do the job. I would be grateful if you could share your demos for imrect and rbbox. I would study them in great detail. Thank you in advance.

[Image Analyst]

imfreehand demo:

% Demo to have the user freehand draw an irregular shape over
% a gray scale image, have it extract only that part to a new image,
% and to calculate the mean intensity value of the image within that shape.
% Also calculates the perimeter, centroid, and center of mass (weighted centroid).

% Change the current folder to the folder of this m-file.
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end
clc;  % Clear command window.
clear;  % Delete all variables.
close all;  % Close all figure windows except those created by imtool.
imtool close all;  % Close all figure windows created by imtool.
workspace;  % Make sure the workspace panel is showing.
fontSize = 16;

% 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);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize);
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
message = sprintf('Left click and hold to begin drawing.\nSimply lift the mouse button to finish');
uiwait(msgbox(message));
hFH = imfreehand();
% Create a binary image ("mask") from the ROI object.
binaryImage = hFH.createMask();
xy = hFH.getPosition;

% Now make it smaller so we can show more images.
subplot(2, 3, 1);
imshow(grayImage, []);
axis on;
drawnow;
title('Original Grayscale Image', 'FontSize', fontSize);

% Display the freehand mask.
subplot(2, 3, 2);
imshow(binaryImage);
axis on;
title('Binary mask of the region', 'FontSize', fontSize);

% Label the binary image and computer the centroid and center of mass.
labeledImage = bwlabel(binaryImage);
measurements = regionprops(binaryImage, grayImage, ...
    'area', 'Centroid', 'WeightedCentroid', 'Perimeter');
area = measurements.Area
centroid = measurements.Centroid
centerOfMass = measurements.WeightedCentroid
perimeter = measurements.Perimeter

% Calculate the area, in pixels, that they drew.
numberOfPixels1 = sum(binaryImage(:))
% Another way to calculate it that takes fractional pixels into account.
numberOfPixels2 = bwarea(binaryImage)

% Get coordinates of the boundary of the freehand drawn region.
structBoundaries = bwboundaries(binaryImage);
xy=structBoundaries{1}; % Get n by 2 array of x,y coordinates.
x = xy(:, 2); % Columns.
y = xy(:, 1); % Rows.
subplot(2, 3, 1); % Plot over original image.
hold on; % Don't blow away the image.
plot(x, y, 'LineWidth', 2);
drawnow; % Force it to draw immediately.

% Burn line into image by setting it to 255 wherever the mask is true.
burnedImage = grayImage;
burnedImage(binaryImage) = 255;
% Display the image with the mask "burned in."
subplot(2, 3, 3);
imshow(burnedImage);
axis on;
caption = sprintf('New image with\nmask burned into image');
title(caption, 'FontSize', fontSize);

% Mask the image and display it.
% Will keep only the part of the image that's inside the mask, zero outside mask.
blackMaskedImage = grayImage;
blackMaskedImage(~binaryImage) = 0;
subplot(2, 3, 4);
imshow(blackMaskedImage);
axis on;
title('Masked Outside Region', 'FontSize', fontSize);
% Calculate the mean
meanGL = mean(blackMaskedImage(binaryImage));

% Put up crosses at the centriod and center of mass
hold on;
plot(centroid(1), centroid(2), 'r+', 'MarkerSize', 30, 'LineWidth', 2);
plot(centerOfMass(1), centerOfMass(2), 'g+', 'MarkerSize', 20, 'LineWidth', 2);

% Now do the same but blacken inside the region.
insideMasked = grayImage;
insideMasked(binaryImage) = 0;
subplot(2, 3, 5);
imshow(insideMasked);
axis on;
title('Masked Inside Region', 'FontSize', fontSize);

% Now crop the image.
leftColumn = min(x);
rightColumn = max(x);
topLine = min(y);
bottomLine = max(y);
width = rightColumn - leftColumn + 1;
height = bottomLine - topLine + 1;
croppedImage = imcrop(blackMaskedImage, [leftColumn, topLine, width, height]);
% Display cropped image.
subplot(2, 3, 6);
imshow(croppedImage);
axis on;
title('Cropped Image', 'FontSize', fontSize);

% Put up crosses at the centriod and center of mass
hold on;
plot(centroid(1)-leftColumn, centroid(2)-topLine, 'r+', 'MarkerSize', 30, 'LineWidth', 2);
plot(centerOfMass(1)-leftColumn, centerOfMass(2)-topLine, 'g+', 'MarkerSize', 20, 'LineWidth', 2);

% Report results.
message = sprintf('Mean value within drawn area = %.3f\nNumber of pixels = %d\nArea in pixels = %.2f\nperimeter = %.2f\nCentroid at (x,y) = (%.1f, %.1f)\nCenter of Mass at (x,y) = (%.1f, %.1f)\nRed crosshairs at centroid.\nGreen crosshairs at center of mass.', ...
meanGL, numberOfPixels1, numberOfPixels2, perimeter, ...
centroid(1), centroid(2), centerOfMass(1), centerOfMass(2));
msgbox(message);

[Image Analyst]

Circle masking demo:

% Demo to mask an image with a circle.
% Requires the Image Processing Toolbox.
%
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.
fontSize = 20;

% Change the current folder to the folder of this m-file.
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end
  
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
fullFileName = fullfile(folder, baseFileName);
% See if the image exists.
if ~exist(fullFileName, 'file')
  % Doesn't exist in that folder. See if it exists anywhere on the path.
  fullFileName = baseFileName;
  if ~exist(fullFileName, 'file')
    errorMessage = sprintf('Error: file %s not found', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
% Read in the image from disk.
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, []);
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Position', get(0,'Screensize')); 
set(gcf,'name','Image Analysis Demo','numbertitle','off') 

% Initialize parameters for the circle,
% such as it's location and radius.
circleCenterX = 130; 
circleCenterY =  75; % square area 0f 500*500 
circleRadius = 50;    % big circle radius 

% Initialize an image to a logical image of the circle. 
circleImage = false(rows, columns); 
[x, y] = meshgrid(1:rows, 1:columns); 
circleImage((x - circleCenterX).^2 + (y - circleCenterY).^2 <= circleRadius.^2) = true; 
% Display it in the upper right plot. 
subplot(2,2,2); 
imshow(circleImage, []); 
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Circle Mask', 'FontSize', fontSize); 
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.

% Mask the image with the circle.
maskedImage = grayImage; % Initialize with the entire image.
maskedImage(~circleImage) = 0; % Zero image outside the circle mask.
% Display it in the lower right plot. 
subplot(2, 3, 5); 
imshow(maskedImage, []); 
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Image masked with the circle.', 'FontSize', fontSize);

[Image Analyst]

Magic Wand demo:

% Demo to do similar to what the Magic Wand does in Photoshop.
% Only tested on gray scale images.
clc;  % Clear command window.
clear;  % Delete all variables.
close all;  % Close all figure windows except those created by imtool.
imtool close all;  % Close all figure windows created by imtool.
workspace;  % Make sure the workspace panel is showing.
fontSize = 15;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
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
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, 'Position', get(0,'Screensize')); 
set(gcf,'name','Image Analysis Demo','numbertitle','off') 

uiwait(msgbox('Click a point'));
[x, y] = ginput(1);
row = max([int32(y) 1]);
column = max([int32(x) 1]);
% Get the gray level of the point they clicked on.
grayLevel = grayImage(row, column);
tolerance = 10;

% Construct abinary image within the gray level tolerance 
% of where they clicked.
lowGL = grayLevel - tolerance;
highGL = grayLevel + tolerance;
binaryImage = grayImage >= lowGL & grayImage <= highGL;
subplot(2, 2, 2);
imshow(binaryImage, []);
caption = sprintf('Binary Image within \n+/- %d Gray Levels of %d', ...
  tolerance, grayLevel);
title(caption, 'FontSize', fontSize);

% Get a marker image to reconstruct just the connected region
% and not all the other disconnected regions.
binaryMarkerImage = logical(zeros(rows, columns));
binaryMarkerImage(row, column) = true;

outputImage = imreconstruct(binaryMarkerImage, binaryImage);
subplot(2, 2, 3);
imshow(outputImage, []);
title('Magic Wand Reconstructed Binary Image', 'FontSize', fontSize);

% Get the masked image - the original image in the region.
maskedImage = zeros(rows, columns, 'uint8');
maskedImage(outputImage) = grayImage(outputImage);
subplot(2, 2, 4);
imshow(maskedImage, [0 255]);
title('Magic Wand Grayscale Image', 'FontSize', fontSize);

msgbox('Done with demo');

[Image Analyst]

imcrop demo:

% Demo macro to extract frames and get frame means from an avi movie
% and save individual frames to separate image files.
% Also computes the mean gray value of the color channels.
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.
fontSize = 14;

% Change the current folder to the folder of this m-file.
% (The line of code below is from Brett Shoelson of The Mathworks.)
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end

% Open the rhino.avi demo movie that ships with MATLAB.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
movieFullFileName = fullfile(folder, 'rhinos.avi');
% Check to see that it exists.
if ~exist(movieFullFileName, 'file')
  strErrorMessage = sprintf('File not found:\n%s\nYou can choose a new one, or cancel', movieFullFileName);
  response = questdlg(strErrorMessage, 'File not found', 'OK - choose a new movie.', 'Cancel', 'OK - choose a new movie.');
  if strcmpi(response, 'OK - choose a new movie.')
    [baseFileName, folderName, FilterIndex] = uigetfile('*.avi');
    if ~isequal(baseFileName, 0)
      movieFullFileName = fullfile(folderName, baseFileName);
    else
      return;
    end
  else
    return;
  end
end

try
  videoObject = VideoReader(movieFullFileName)
  % Determine how many frames there are.
  numberOfFrames = videoObject.NumberOfFrames;
  vidHeight = videoObject.Height;
  vidWidth = videoObject.Width;
  
  numberOfFramesWritten = 0;
  % Prepare a figure to show the images in the upper half of the screen.
  figure;
  %   screenSize = get(0, 'ScreenSize');
  % Enlarge figure to full screen.
  set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
  
  % Ask user if they want to write the individual frames out to disk.
  promptMessage = sprintf('Do you want to save the individual frames out to individual disk files?');
  button = questdlg(promptMessage, 'Save individual frames?', 'Yes', 'No', 'Yes');
  if strcmp(button, 'Yes')
    writeToDisk = true;
    
    % Extract out the various parts of the filename.
    [folder, baseFileName, extentions] = fileparts(movieFullFileName);
    % Make up a special new output subfolder for all the separate
    % movie frames that we're going to extract and save to disk.
    % (Don't worry - windows can handle forward slashes in the folder name.)
    folder = pwd;   % Make it a subfolder of the folder where this m-file lives.
    outputFolder = sprintf('%s/Movie Frames from %s', folder, baseFileName);
    % Create the folder if it doesn't exist already.
    if ~exist(outputFolder, 'dir')
      mkdir(outputFolder);
    end
  else
    writeToDisk = false;
  end
  
  % Loop through the movie, writing all frames out.
  % Each frame will be in a separate file with unique name.
  meanGrayLevels = zeros(numberOfFrames, 1);
  meanRedLevels = zeros(numberOfFrames, 1);
  meanGreenLevels = zeros(numberOfFrames, 1);
  meanBlueLevels = zeros(numberOfFrames, 1);
  for frame = 1 : numberOfFrames
    % Extract the frame from the movie structure.
    thisFrame = read(videoObject, frame);
    
    % Display it
    hImage = subplot(2, 2, 1);
    image(thisFrame);
    caption = sprintf('Frame %4d of %d.', frame, numberOfFrames);
    title(caption, 'FontSize', fontSize);
    drawnow; % Force it to refresh the window.
    
    % Write the image array to the output file, if requested.
    if writeToDisk
      % Construct an output image file name.
      outputBaseFileName = sprintf('Frame %4.4d.png', frame);
      outputFullFileName = fullfile(outputFolder, outputBaseFileName);
      
      % Stamp the name and frame number onto the image.
      % At this point it's just going into the overlay,
      % not actually getting written into the pixel values.
      text(5, 15, outputBaseFileName, 'FontSize', 20);
      
      % Extract the image with the text "burned into" it.
      frameWithText = getframe(gca);
      % frameWithText.cdata is the image with the text
      % actually written into the pixel values.
      % Write it out to disk.
      imwrite(frameWithText.cdata, outputFullFileName, 'png');
    end
    
    % Calculate the mean gray level.
    grayImage = rgb2gray(thisFrame);
    meanGrayLevels(frame) = mean(grayImage(:));
    
    % Calculate the mean R, G, and B levels.
    meanRedLevels(frame) = mean(mean(thisFrame(:, :, 1)));
    meanGreenLevels(frame) = mean(mean(thisFrame(:, :, 2)));
    meanBlueLevels(frame) = mean(mean(thisFrame(:, :, 3)));
    
    % Plot the mean gray levels.
    hPlot = subplot(2, 2, 2);
    hold off;
    plot(meanGrayLevels, 'k-', 'LineWidth', 2);
    hold on;
    plot(meanRedLevels, 'r-');
    plot(meanGreenLevels, 'g-');
    plot(meanBlueLevels, 'b-');
    grid on;
    
    % Put title back because plot() erases the existing title.
    title('Mean Gray Levels', 'FontSize', fontSize);
    if frame == 1
      xlabel('Frame Number');
      ylabel('Gray Level');
      % Get size data later for preallocation if we read
      % the movie back in from disk.
      [rows columns numberOfColorChannels] = size(thisFrame);
    end
    
    % Update user with the progress.  Display in the command window.
    if writeToDisk
      progressIndication = sprintf('Wrote frame %4d of %d.', frame, numberOfFrames);
    else
      progressIndication = sprintf('Processed frame %4d of %d.', frame, numberOfFrames);
    end
    disp(progressIndication);
    % Increment frame count (should eventually = numberOfFrames
    % unless an error happens).
    numberOfFramesWritten = numberOfFramesWritten + 1;
    
    % Now let's do the differencing
    alpha = 0.5;
    if frame == 1
      Background = thisFrame;
    else
      % Change background slightly at each frame
      %       Background(t+1)=(1-alpha)*I+alpha*Background
      Background = (1-alpha)* thisFrame + alpha * Background;
    end
    % Display the changing/adapting background.
    subplot(2, 2, 3);
    imshow(Background);
    title('Adaptive Background', 'FontSize', fontSize);
    % Calculate a difference between this frame and the background.
    differenceImage = thisFrame - uint8(Background);
    % Threshold with Otsu method.
    grayImage = rgb2gray(differenceImage); % Convert to gray level
    thresholdLevel = graythresh(grayImage); % Get threshold.
    binaryImage = im2bw( grayImage, thresholdLevel); % Do the binarization
    % Plot the binary image.
    subplot(2, 2, 4);
    imshow(binaryImage);
    title('Binarized Difference Image', 'FontSize', fontSize);
  end
  
  % Alert user that we're done.
  if writeToDisk
    finishedMessage = sprintf('Done!  It wrote %d frames to folder\n"%s"', numberOfFramesWritten, outputFolder);
  else
    finishedMessage = sprintf('Done!  It processed %d frames of\n"%s"', numberOfFramesWritten, movieFullFileName);
  end
  disp(finishedMessage); % Write to command window.
  uiwait(msgbox(finishedMessage)); % Also pop up a message box.
  
  % Exit if they didn't write any individual frames out to disk.
  if ~writeToDisk
    return;
  end
  
  % Ask user if they want to read the individual frames from the disk,
  % that they just wrote out, back into a movie and display it.
  promptMessage = sprintf('Do you want to recall the individual frames\nback from disk into a movie?\n(This will take several seconds.)');
  button = questdlg(promptMessage, 'Recall Movie?', 'Yes', 'No', 'Yes');
  if strcmp(button, 'No')
    return;
  end
  
  % Read the frames back in from disk, and convert them to a movie.
  % Preallocate recalledMovie, which will be an array of structures.
  % First get a cell array with all the frames.
  allTheFrames = cell(numberOfFrames,1);
  allTheFrames(:) = {zeros(vidHeight, vidWidth, 3, 'uint8')};
  % Next get a cell array with all the colormaps.
  allTheColorMaps = cell(numberOfFrames,1);
  allTheColorMaps(:) = {zeros(256, 3)};
  % Now combine these to make the array of structures.
  recalledMovie = struct('cdata', allTheFrames, 'colormap', allTheColorMaps)
  for frame = 1 : numberOfFrames
    % Construct an output image file name.
    outputBaseFileName = sprintf('Frame %4.4d.png', frame);
    outputFullFileName = fullfile(outputFolder, outputBaseFileName);
    % Read the image in from disk.
    thisFrame = imread(outputFullFileName);
    % Convert the image into a "movie frame" structure.
    recalledMovie(frame) = im2frame(thisFrame);
  end
  % Get rid of old image and plot.
  delete(hImage);
  delete(hPlot);
  % Create new axes for our movie.
  subplot(1, 3, 2);
  axis off;  % Turn off axes numbers.
  title('Movie recalled from disk', 'FontSize', fontSize);
  % Play the movie in the axes.
  movie(recalledMovie);
  % Note: if you want to display graphics or text in the overlay
  % as the movie plays back then you need to do it like I did at first
  % (at the top of this file where you extract and imshow a frame at a time.)
  msgbox('Done with this demo!');
  
catch ME
  % Some error happened if you get here.
  stError = lasterror;
  strErrorMessage = sprintf('Error extracting movie frames from:\n\n%s\n\nError: %s\n\n)', movieFullFileName, stError.message);
  uiwait(msgbox(strErrorMessage));
end

Answer 2

[Azzi Abdelmalek]

You can use imrect function