MATLAB Functions

Set and get the current colormap

colormap(map)
colormap('default')
cmap = colormap

Description

A colormap is an m-by-3 matrix of real numbers between 0.0 and 1.0. Each row is an RGB vector that defines one color. The kth row of the colormap defines the k-th color, where map(k,:) = [r(k) g(k) b(k)]) specifies the intensity of red, green, and blue.

colormap(map)

sets the colormap to the matrix map. If any values in map are outside the interval [0 1], MATLAB returns the error: Colormap must have values in [0,1]

colormap('default')

sets the current colormap to the default colormap.

cmap = colormap;

retrieves the current colormap. The values returned are in the interval [0 1].

Specifying Colormaps

M-files in the color directory generate a number of colormaps. Each M-file accepts the colormap size as an argument. For example,

colormap(hsv(128))

creates an hsv colormap with 128 colors. If you do not specify a size, MATLAB creates a colormap the same size as the current colormap.

Supported Colormaps

MATLAB supports a number of colormaps.

autumn varies smoothly from red, through orange, to yellow.
bone is a grayscale colormap with a higher value for the blue component. This colormap is useful for adding an "electronic" look to grayscale images.
colorcube contains as many regularly spaced colors in RGB colorspace as possible, while attempting to provide more steps of gray, pure red, pure green, and pure blue.
cool consists of colors that are shades of cyan and magenta. It varies smoothly from cyan to magenta.
copper varies smoothly from black to bright copper.
flag consists of the colors red, white, blue, and black. This colormap completely changes color with each index increment.
gray returns a linear grayscale colormap.
hot varies smoothly from black, through shades of red, orange, and yellow, to white.
hsv varies the hue component of the hue-saturation-value color model. The colors begin with red, pass through yellow, green, cyan, blue, magenta, and return to red. The colormap is particularly appropriate for displaying periodic functions. hsv(m) is the same as hsv2rgb([h ones(m,2)]) where h is the linear ramp, h = (0:m-1)'/m.
jet ranges from blue to red, and passes through the colors cyan, yellow, and orange. It is a variation of the hsv colormap. The jet colormap is associated with an astrophysical fluid jet simulation from the National Center for Supercomputer Applications. The following commands display the flujet data using the jet colormap:

    load flujet
    image(X)
    colormap(jet)

lines produces a colormap of colors specified by the Axes ColorOrder property and a shade of gray.
pink contains pastel shades of pink. The pink colormap provides sepia tone colorization of grayscale photographs.
prism repeats the six colors red, orange, yellow, green, blue, and violet.
spring consists of colors that are shades of magenta and yellow.
summer consists of colors that are shades of green and yellow.
white is an all white monochrome colormap.
winter consists of colors that are shades of blue and green.

Examples

The Images and colormaps demo, imagedemo, provides an introduction to colormaps. Select Color Spiral from the menu (starts automatically on the Macintosh). This uses the pcolor function to display a 16-by-16 matrix whose elements vary from 0 to 255 in a rectilinear spiral. The hsv colormap starts with red in the center, then passes through yellow, green, cyan, blue, and magenta before returning to red at the outside end of the spiral. Selecting Colormap Menu gives access to a number of other colormaps (except for on the Macintosh).

The rgbplot function plots colormap values. Try rgbplot(hsv), rgbplot(gray), and rgbplot(hot).

The demos directory contains a CAT scan image of a human spine. To view the image:

load spine 
image(X)
colormap bone

Algorithm

Each Figure has its own ColorMap property. colormap is an M-file that sets and gets this property.