MATLAB: Trouble with image importing

image importingimage processing

In my project, which focuses on image processing techniques, I have a significant fundamental problem. When I try to import a black and white or grayscale image, matlab interprets it as a three-dimensional matrix, where I guess the third matrix is a color map (even though we aren't using color images). I have used the command rbgtogray, and while that solves the dimension problem, the result is always an image that is not gray. Is there something I'm missing?

Best Answer

Right, now we've got to the bottom of the problem:

You're using the wrong function to display your image. Instead of

image(I); %or I2

Use

imshow(I); % or I2

As per documentation of image, image creates an image graphics object by interpreting each element in a matrix as an index into the figure's colormap. Another option would be to change the figure colormap to greyscale with

colormap([0:255; 0:255; 0:255]' / 255);

Related Solutions

MATLAB: To display an 8bit image

If you want to zero out the red and blue channels of your RGB image, you can do this:

rgbImage(:, :, [1, 3]) = 0;
imshow(rgbImage);

The reason that it was appearing gray is that the red and blue channels are the same as the green channel. Zeroing them out will make it look green.

Alternatively you can extract the green channel and apply a colormap.

rgbImage = imread('peppers.png'); % Sample image.
greenChannel = rgbImage(:, :, 2); % Extract green channel
z = zeros(256, 1);
ramp = (0:255)' / 255;
cmap = [z, ramp, z];
colormap(cmap);
colorbar;
imshow(greenChannel, cmap);

MATLAB: Convert grayscale to RGB

Try it like this if you want to pick some color out of the jet colormap:

workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Create a jet colormap
c = 128;
map = jet(c);
pO2value=double(109); % 109 is an arbitrary number out of 1:128
r = ceil(map(pO2value,1)*c)
g = ceil(map(pO2value,2)*c)
b = ceil(map(pO2value,3)*c)
% Now let's do it to a gray scale image.
% Read in a standard MATLAB gray scale demo image.
grayImage = imread('cameraman.tif');
handleToFigure2 = figure;
subplot(2,2,1);
imshow(grayImage);
title('Gray Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Convert the gray image into RGB so we can get it into hsv space.
rgbImage = cat(3, grayImage, grayImage, grayImage);
hsv = rgb2hsv(rgbImage);
% Make the hue plane of the hsv image this same hue
hsvOfThisPixel = rgb2hsv([r g b])
hsv(:, :, 1) = hsvOfThisPixel(1);
% Make the saturation 1 so we'll see color.
% Originally it was zero which meant that the image would be gray.
hsv(:, :, 2) = 1;
% Convert back to rgb space.
singleHueRGBImage = uint8(255*hsv2rgb(hsv));
% Display the new, single hue color image.
subplot(2, 2, 2);
imshow(singleHueRGBImage);
title('New, Single Hue Color Image', 'FontSize', fontSize);
message = sprintf('Done with demo.');
uiwait(msgbox(message));

Best Answer

Related Solutions

MATLAB: To display an 8bit image

MATLAB: Convert grayscale to RGB

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