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add edge thinning to canny

This commit is contained in:
John Cupitt 2018-02-03 10:14:09 +00:00
parent a93e8dd079
commit 6944f78452
1 changed files with 37 additions and 14 deletions
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51
libvips/convolution/canny.c
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@ -144,7 +144,9 @@ vips_canny_nonmax_generate( VipsRegion *or,
VipsRect rect;
int x, y, band;
int lsk;
int
int psk;
int offseta[4];
int offsetb[4];
rect = *r;
rect.width += 2;
@ -152,6 +154,19 @@ vips_canny_nonmax_generate( VipsRegion *or,
if( vips_region_prepare( in, &rect ) )
return( -1 );
lsk = VIPS_REGION_LSKIP( in );
psk = VIPS_IMAGE_SIZEOF_PEL( im );
/* For each of the four directions, the offset to get to that pixel
* from the top-left of our 3x3.
*/
offseta[0] = psk;
offsetb[0] = psk + 2 * lsk;
offseta[1] = 2 * psk;
offsetb[1] = 2 * lsk;
offseta[2] = 2 * psk + lsk;
offsetb[2] = lsk;
offseta[3] = 0;
offsetb[3] = 2 * psk + 2 * lsk;
for( y = 0; y < r->height; y++ ) {
VipsPel *p = (VipsPel * restrict)
@ -161,20 +176,19 @@ vips_canny_nonmax_generate( VipsRegion *or,
for( x = 0; x < r->width; x++ ) {
for( band = 0; band < im->Bands; band++ ) {
int G = p[0];
int theta = p[1];
int G = p[lsk + psk];
int theta = p[lsk + psk + 1];
VipsPel low = p[offseta[theta]];
VipsPel high = p[offsetb[theta]];
int v1, v2;
/* Set G to 0 if it's not the local maxima in
* the direction of the gradient.
*/
if( G < low ||
G < high )
G = 0;
if( theta == 0 ) {
v1 = p[
switch( theta ) {
case 0:
q[band] = x;
q[band] = G;
p += 2;
}
@ -193,7 +207,7 @@ static int
vips_canny_nonmax( VipsImage *in, VipsImage **out )
{
*out = vips_image_new();
if( vips_image_pipeline_arrayv( *out,
if( vips_image_pipelinev( *out,
VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
return( -1 );
(*out)->Bands /= 2;
@ -262,6 +276,15 @@ vips_canny_build( VipsObject *object )
return( -1 );
in = t[9];
/* Expand by two pixels all around, then thin.
*/
if( vips_embed( in, &t[10], 1, 1, in->Xsize, in->Ysize,
"extend", VIPS_EXTEND_COPY,
NULL ) ||
vips_canny_nonmax( t[10], &t[11] ) )
return( -1 );
in = t[11];
g_object_set( object, "out", vips_image_new(), NULL );
if( vips_image_write( in, canny->out ) )