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THRESMLWAHA

Section: C Library Functions (3)
Updated: 16 Mar 1998
Index

NAME

thresMlWaHa - Finds multiple thresholds by Wang & Haralickmethod.

SYNTAX

int thresMlWaHa( IBAND gray, IBAND tri,
    IBAND edge, int thVect[], int edgeTh,
    int numTh, int population, int n,
    int* totTh );

DESCRIPTION

The pixels in grayare first classified as either edgepixels or nonedge pixels. Edge pixels are then classified, onthe basis of their neighborhoods, as being relatively dark,relatively bright or gray. A histogram of the graytoneintensities is obtained for those pixels which are edgepixels and relatively dark, and another histogram is obtainedfor those which are edge pixels and relatively bright. Twocandidate thresholds are found at the intensity valuescorresponding to peaks in the two histograms. The thresholdgiving the highest probability of getting pure dark or brightregions is selected. If the selected threshold corresponds tothe peak in the dark edge histogram, the process is repeatedfor the graytone range above the threshold, if the thresholdcorresponds to the peak in the bright edge histogram, theprocess is repeated for the graytone range below thethreshold.

You can specify the number of thresholds to be found, or aminimum population of the two histograms at which to stop.The population of the two histograms decreases rapidly, andmight reach zero before the specified number of thresholds isfound. There is no peak in a histogram with only zero entriesand the process stops.

PARAMETERS

gray

The inband to be thresholded.

tri

A band to hold the tri-tone edge band. Can be NULL.

edge

A band to hold the sobel magnitude edge band. Can be NULL.

thVect

A 256 element int vector returning the threshold values inincreasing order. The number of thresholds found are returnedthrough the argument totTh.

edgeTh

The threshold-value at wich to threshold the edgeband.

numTh

The number of thresholds wanted.

pop

The minimum population allowed for the dark/bright edgehistograms. One and only one of numThand popmust bespecified, the other one should be zero.

n

An integer used to adjust the number of edge pixels classifiedas either dark or bright. The number of pixels classified aseither dark or bright increases with increasing n.Must bepositive and non-zero, usually n= 3.

totTh

The number of thresholds found.

REFERENCE

S. Wang and R. M. Haralick

"Automatic Multithreshold Selection".Computer Vision, Graphics, and Image Processing,25, 46-67 (1984).

RESTRICTIONS

gray,triand edgemust have pixel type unsigned byte.

RETURN VALUE

Status value:
    0 => ok
    1 => None or both "numTh" and "pop" specified.
    2 => Wrong pixeltype in "gray".
    3 => Wrong pixeltype in "tri".
    4 => Wrong pixeltype in "edge".
    5 => Malloc error. Not able to create temporary image.
    6 => "tri" size different from "gray" size.
    7 => "edge" size different from "gray" size.
    8 => "n" < 1.
    9 => No thresholds found.

AUTHOR

Jřrn Tilley Jacobsen, BLAB, Ifi, UiO

ID

$Id: thresMlWaHa.c,v 1.22 1997/01/14 13:09:28 svein Exp $

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