MATLAB: Cameraman.tif is an indexed image

image processing

Is the image "cameraman.tif" an indexed image?

[I , map] = imread('cameraman.tif')
size(map) % says an empty matrix

but changing the colormap changes it's color, why?

colormap(jet) % Changes the color of image.

Best Answer

Most likely, 'cameraman.tif' is just a greyscale image.

In any case, colormap works just as well for greyscale images, so is not any indication:

imshow(randi([0 255], 500, 500, 'uint8'));
colormap(summer);

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MATLAB: Colormap function not able to change colormap of an image

Correct - a colormap does not apply for a true color RGB image. RGB images don't have colormaps, which are essentially lookup tables to convert a gray level into a color. To change the color of a pixel in an RGB image you just do it directly by changing the R, G, and B values. There is no single "index" or gray level like there is with an indexed image. If you want to convert your RGB image into an indexed image, you can do so with the rgb2gray() function. Or you can do color segmentation (like in my File Exchange http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862 ) to identify some region of the image that matches some criteria you specify, and then create a binary image to change whole regions into the desired color.

MATLAB: How to create a white image

Try this to create a grayscale image:

whiteImage = 255 * ones(N, M, 'uint8');
imshow(whiteImage);

To create an RGB image, try this:

whiteImage = 255 * ones(480, 640, 3, 'uint8');
imshow(whiteImage);

Best Answer

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