MATLAB: Show a ROI over the original image

Question

Hi friends;

I´m using imfreehand to select a region (roi) on a greyscale image in order to show this roi over the greyscale image. The question is…I would like to attribute a colormap for the roi (like to open it using imagesc), however I don´t know how to do that. My code is:

if true
  i = imread('cameraman.tif');
imshow(i);
h = imfreehand;
mask = createMask(h);
i(~mask) = NaN;
figure;
image(i);
j = imread('cameraman.tif');
mergeim = imadd(j,i);
figure;
imshow(mergeim);
end

Answer 1

Henrique, see the demo code below that I wrote to produce this figure:

% Demo to have the user freehand draw an irregular shape over
% a gray scale image, have it convert that portion to a
% color RGB image defined by a colormap.
clc;  % Clear command window.
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, 2, 1);
imshow(grayImage, []);
axis on;
drawnow;
title('Original Grayscale Image', 'FontSize', fontSize);
% Display the freehand mask.
subplot(2, 2, 2);
imshow(binaryImage);
axis on;
title('Binary mask of the region', 'FontSize', fontSize);
% Convert the grayscale image to RGB using the jet colormap.
rgbImage = ind2rgb(grayImage, jet(256));
% Scale and convert from double (in the 0-1 range) to uint8.
rgbImage = uint8(255*rgbImage);
% Display the RGB image.
subplot(2, 2, 3);
imshow(rgbImage);
axis on;
title('RGB Image from Jet Colormap', 'FontSize', fontSize);
% Extract the red, green, and blue channels from the color image.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Create a new color channel images for the output.
outputImageR = grayImage;
outputImageG = grayImage;
outputImageB = grayImage;
% Transfer the colored parts.
outputImageR(binaryImage) = redChannel(binaryImage);
outputImageG(binaryImage) = greenChannel(binaryImage);
outputImageB(binaryImage) = blueChannel(binaryImage);
% Convert into an RGB image
outputRGBImage = cat(3, outputImageR, outputImageG, outputImageB);
% Display the output RGB image.
subplot(2, 2, 4);
imshow(outputRGBImage);
axis on;
title('Output RGB Image', 'FontSize', fontSize);