LABEL_REGION

The LABEL_REGION function consecutively labels all of the regions, or blobs, of a bi-level image with a unique region index. This process is sometimes called "blob coloring". A region is a set of non-zero pixels within a neighborhood around the pixel under examination.

The argument for LABEL_REGION is an n-dimensional bi-level integer type array—only zero and non-zero values are considered.

Statistics on each of the regions may be easily calculated using the HISTOGRAM function as shown in the examples below.

Syntax

Result = LABEL_REGION( Data [, /ALL_NEIGHBORS] [, /ULONG] )

Return Value

The result of the function is an integer array of the same dimensions with each pixel containing its region index. A region index of zero indicates that the original pixel was zero and belongs to no region. Output values range from 0 to the number of regions.

Arguments

Data

A n-dimensional image to be labeled. Data is converted to integer type if necessary. Pixels at the edges of Data are considered to be zero.

Keywords

ALL_NEIGHBORS

Set this keyword to indicate that all adjacent neighbors to a given pixel should be searched. (This is sometimes called 8-neighbor searching when the image is 2-dimensional). The default is to search only the neighbors that are exactly one unit in distance from the current pixel (sometimes called 4-neighbor searching when the image is 2-dimensional).

ULONG

Set this keyword to specify that the output array should be an unsigned long integer.

Examples

Note
Also see Analyzing Image Shapes (Image Processing in IDL).

Example 1

This example counts the number of distinct regions within an image, and their population. Note that region 0 is the set of zero pixels that are not within a region:

image = DIST(40)

; Get blob indices:
b = LABEL_REGION(image)

; Get population of each blob:
h = HISTOGRAM(b)
FOR i=0, N_ELEMENTS(h)-1 DO PRINT, 'Region ',i, $
', Population = ', h[i]

Example 2

This example also prints the average value and standard deviation of each region:

PRO label_region_ex_2

image = DIST(40)

; Get blob indices:
b = LABEL_REGION(image)

; Get population and members of each blob:
h = HISTOGRAM(b, REVERSE_INDICES=r)

; Each region
FOR i=0, N_ELEMENTS(h)-1 DO BEGIN
   ;Find subscripts of members of region i.
   p = r[r[i]:r[i+1]-1]

   ; Pixels of region i
   q = image[p]
   PRINT, 'Region ', i, $
      ', Population = ', h[i], $
      ', Standard Deviation = ', STDEV(q, mean), $
      ', Mean = ', mean
ENDFOR
END

label_region_ex_2

Version History


Pre 4.0	Introduced
Pre 6.1	Deprecated the EIGHT keyword

For more information on deprecated features, see IDL API History.