MATLAB: Show a ROI over the original image


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');
h = imfreehand;
mask = createMask(h);
i(~mask) = NaN;
j = imread('cameraman.tif');
mergeim = imadd(j,i);

Best Answer

  • 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);
    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');
    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;
    title('Original Grayscale Image', 'FontSize', fontSize);
    % Display the freehand mask.
    subplot(2, 2, 2);
    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);
    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);
    axis on;
    title('Output RGB Image', 'FontSize', fontSize);