label2rgb (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Convert a label matrix into an RGB image

Syntax

RGB = label2rgb(L)
RGB = label2rgb(L,map)
RGB = label2rgb(L,map,zerocolor)
RGB = label2rgb(L,map,zerocolor,order)

Description

RGB = label2rgb(L) converts a label matrix L, such as those returned by bwlabel or watershed, into an RGB color image for the purpose of visualizing the labeled regions. The label2rgb function determines the color to assign to each object based on the number of objects in the label matrix and range of colors in the colormap. The label2rgb function picks colors from the entire range.

RGB = label2rgb(L,map) defines the colormap map to be used in the RGB image. map can have any of the following values:

n-by-3 colormap matrix
String containing the name of a MATLAB colormap function, such as 'jet' or 'gray' (See colormap for a list of supported colormaps.)
Function handle of a colormap function, such as @jet or @gray

If you do not specify map, the default value is 'jet'.

RGB = label2rgb(L,map,zerocolor) defines the RGB color of the elements labeled 0 (zero) in the input label matrix L. As the value of zerocolor, specify an RGB triple or one of the strings listed in this table.

Value
Color

'b'
Blue

'c'
Cyan

'g'
Green

'k'
Black

'm'
Magenta

'r'
Red

'w'
White

'y'
Yellow

Value	Color
`'b'`	Blue
`'c'`	Cyan
`'g'`	Green
`'k'`	Black
`'m'`	Magenta
`'r'`	Red
`'w'`	White
`'y'`	Yellow

If you do not specify zerocolor, the default value for zero-labeled elements is [1 1 1] (white).

RGB = label2rgb(L,map,zerocolor,order) controls how label2rgb assigns colormap colors to regions in the label matrix. If order is 'noshuffle' (the default), label2rgb assigns colormap colors to label matrix regions in numerical order. If order is 'shuffle', label2rgb assigns colormap colors pseudorandomly.

Class Support

The input label matrix L can have any nonsparse, numeric class. It must contain finite, nonnegative integers. The output of label2rgb is of class uint8.

Example

I = imread('rice.png'); 
figure, imshow(I), title('original image') 
BW = im2bw(I, graythresh(I)); 
L = bwlabel(BW); 
RGB = label2rgb(L); 
RGB2 = label2rgb(L, 'spring', 'c', 'shuffle'); 
imshow(RGB), figure, imshow(RGB2)

See Also

bwlabel, colormap, ismember, watershed

lab2uint8 makecform