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CANNY

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

NAME

canny, canny_filters, canny_scale - detect edges in imageusing Canny operator

SYNTAX

int canny( IBAND input, IBAND magnitude,
    IBAND angle, IBAND laplace, int lngth,
    int h1[], int h2[], int h3[], double scale,
    int thin, int verbose );

int canny_filters( float sigma, int k, int h1[],
int h2[], int h3[], int verbose );

double canny_scale( double sigma, int k );

DESCRIPTION

cannyperforms the canny edge detector onthe input image input.Output from the functionare the edge magnitude,the edge angleandthe laplace.The filter is specified by agaussian function h1,the first derivative h2,and the second derivative h3,all of length lngth.The outputs are scaled down with a factor scale.If thinis true, thinning of the edge is performed.The function may be silent or verbose.

canny_filterscomputes the filters h1,h2,and h3.based on sigmaand k.The function returns the filterlength. You may try sigma=1.0 .. 7.0 and k=200 .. 500.John Canny has used 2.0 and 450 as default values.

canny_scalereturns a default scale value based onsigmaand magnification k.

RESTRICTIONS

The current implementation has a maximum filter lengthof 50, and a maximum input image width of 1024.

All the band parameters in cannymust have pixel typeunsigned byte.

RETURN VALUE

For canny_scale

The default scale value.

For canny_filters

Filter length.

For canny

0 : Ok
1 : Bad pixeltype
2 : Filter length too large
3 : Input image too small compared to filter
length

REFERENCE

John Canny: A computational Approach to Edge Detection.IEEE Transactions on Pattern analysis and Machine Int.Vol. PAMI-8 No 6 Nov. 1986

AUTHOR

Paul Kloschinsky
Modified for XITE by Otto Milvang and Svein Bře.

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