MATLAB: How to eliminate colormap

digital image processingimage analysisimage processing

a = imread('cameraman.tif') ;
image(a)

The commands are producing the image in a colormap, not in gray tone (original color). I do not want the colormap?

How to fix this without using imshow?

Thanks in advance!

Best Answer

When you supply a 2D array to image(), the values within that array are mapped to a colormap. The colormap is needed to convert scalar values to RGB triplets. imread() returns a 2D array for grayscale images, but you can supply the corresponding 3D array (where R=G=B) to image() if you want:

image(repmat(a,1,1,3))

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clear; clc;
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MATLAB: What is the difference between RGB Image and Colormap

In an RGB image, each pixel is individually supplied with the information about what its Red, Green, and Blue components are. The image can be painted directly.

In a pseudocolor image, each pixel is a single value which is a color number. The color numbers have no independent meaning: color #8 might be completely different than #7 or #9. The color numbers are references to a table of colors that say what the R, G, B components are for each color number. So two pixels that both have color #8 will be looked up in the same table location, and pixels with color #7 would be looked up in an adjacent table location, but the RGB values for the adjacent entries can be completely different.

pseudocolor is a "Paint By Number" set.

You can make a pseudocolor image look quite different visually by changing the colormap without changing the color numbers.

Color numbers do not themselves have any gray-level information; color numbers are just arbitrary. "I'll take whatever color is behind door #3, Bob." RGB images, on the other hand, directly have all the information needed in order to calculate brightness (gray) level.

Best Answer

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