MATLAB: Images appear black and white instead of coloured

.jpgimagesctif

I plot a montage of images onto a UIPanel and it worked fine when the images were tiffs. My images are now jpgs and I notice that the coloured images now appear black and white. I can't see why this would be the case. Here is my code

This is in a loop for all images.

       hp = handles.uipanelM;
       h=subplot('Position',positionVector,'Parent',hp); %to enable deleting use handles
       colormap (jet);
       % update handle array
       hSubplots = [hSubplots ; h];   %Concatenate
       axis off;
       hold off;
       %Create thumbnail sized image
       IM1=imresize(IM, 0.05);
       allImgs{y1,x1} = IM1 ;             
       imagesc(Image,[mlo mhi])
       colormap (jet);
       axis off;
       set(gca,'ytick',[]);
       set(gca,'xtick',[]);
       drawnow;

Best Answer

JPG images are usually color, even if they appear as gray scale - it's just that all the color channels are the same. Try:

imshow(IM1, []);  % Display color image

Or extract one of the color channels:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
imshow(redChannel, []);  % Display one monochrome color channel
colormap(jet(256));

Or convert to grayscale if the color channels are NOT all identical:

grayImage = rgb2gray(IM1);
imshow(grayImage); % Display converted image.
colormap(jet(256));
colorbar;

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MATLAB: How to include a colorbar for an RGB image overlayed with a black & white image

The missing lines are just being subsampled away when you go to display. They're still in the image, just use the magnifying glass to zoom in and you'll see them.

How about this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
image1 = imread('image1.jpg');
% Get the dimensions of the image.  
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(image1);
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Use weighted sum of ALL channels to create a gray scale image.
  image1 = rgb2gray(image1); 
  % ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
  % which in a typical snapshot will be the least noisy channel.
  % grayImage = grayImage(:, :, 2); % Take green channel.
end
% This image is supposed to be binary.
image1 = image1 > 128;
imshow(image1);
hp = impixelinfo();
% Display the image.

subplot(2, 2, 1);
imshow(image1, []);
axis on;
hold on;
title('Image1', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hold on
image2 = imread('image2.jpg');
% Display the image.
subplot(2, 2, 2);
imshow(image2, []);
hp = impixelinfo();
axis on;
hold on;
title('Image2', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
h3 = subplot(2, 2, 3:4);
% Mask the image using bsxfun() function
% maskedRgbImage = bsxfun(@times, image2, cast(image1, 'like', image2));
imshow(image1, []);
hp = impixelinfo();
hold on;
h=imshow(image2);
set(h,'Alphadata', 0.6);
axis on;
theColorMap = jet(256);
theColorMap(1,:) = 0; % First row is black.
theColorMap(end,:) = 1; % last row is white.
colormap(h3, theColorMap);
colorbar(h3);
caxis([0,0.6]);
title('Image1 with Image2 in overlay', 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.05, 1, .95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

MATLAB: How to display the intensity of 2D image as a colormap

You need to pass in a colormap, N-by-3 array with values between 0 and 1, to to the colormap() function, NOT an image. And you should probably also pass in a handles to the axes you want to apply it to, otherwise it will apply that colormap to every axes in the figure window, which is probably not what you want. So in short, you want:

myColorMap = hsv(256);      % Create a colormap.


colormap(gca, myColorMap);  % Now apply the colormap.

You can also pass the colormap directly into imshow() and skip calling the colormap() function if you want.

See this full demo and study it:

grayImage = imread('cameraman.tif');
subplot(3, 1, 1);
imshow(grayImage);
axis('on', 'image');
title('Original Image');
subplot(3, 1, 2);
% Create a colormap.
myColorMap = hsv(256);
% Display image with that colormap.
imshow(grayImage, 'Colormap', myColorMap);
colorbar;
axis('on', 'image');
title('Overlay Image');
% Or equivalently, using the colormap() function:
subplot(3, 1, 3);
% Display image with no colormap.
imshow(grayImage);
% Create a colormap.
myColorMap = hsv(256);
% Now apply the colormap.  Pass in the axes or else it will apply the colormap
% to ALL images on the figure, which is probably not what you want.
colormap(gca, myColorMap);
colorbar;
axis('on', 'image');
title('Overlay Image');

Now, if you already have a colormap, and you want to produce an RGB image, like to write to a file on disk rather than just pseudocoloring a displayed image, you want to call ind2rgb()

rgbImage = ind2rgb(grayImage, myColorMap);

Best Answer

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MATLAB: How to include a colorbar for an RGB image overlayed with a black & white image

MATLAB: How to display the intensity of 2D image as a colormap

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