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try interpolating theta

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This commit is contained in:
John Cupitt 2018-02-05 09:22:58 +00:00
parent ce6d37189c
commit 43cbd32955
1 changed files with 121 additions and 13 deletions
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134
libvips/convolution/canny.c
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@ -88,13 +88,13 @@ vips_canny_polar_generate( VipsRegion *or,
for( band = 0; band < Gx->Bands; band++ ) {
int x = p1[band] - 128;
int y = p2[band] - 128;
int a = 360 + VIPS_DEG( atan2( x, y ) );
int a = VIPS_DEG( atan2( x, y ) ) + 360;
/* Faster than hypot() for int args. Scale down
* or we'll clip on very hard edges.
*/
q[0] = 0.5 * sqrt( x * x + y * y );
q[1] = ((a + 22) / 45) & 0x3;
q[1] = 256 * a / 360;
q += 2;
}
@ -111,13 +111,8 @@ vips_canny_polar_generate( VipsRegion *or,
* code theta as below. Scale G down by 0.5 so that we
* don't clip on hard edges.
*
* For a white disc on a black background, theta is:
*
* 1 | 0 | 3
* --+---+--
* 2 | X | 2
* --+---+--
* 3 | 0 | 1
* For a white disc on a black background, theta is 0 at the bottom, 64 on the
* right, 128 at the top and 192 on the left edge.
*/
static int
vips_canny_polar( VipsImage **args, VipsImage **out )
@ -163,6 +158,12 @@ vips_canny_nonmax_generate( VipsRegion *or,
/* For each of the four directions, the offset to get to that pixel
* from the top-left of our 3x3. offseta is the left/up direction, or
* the lower memory address.
*
* 1 | 0 | 3
* --+---+--
* 2 | X | 2
* --+---+--
* 3 | 0 | 1
*/
offseta[0] = psk;
offsetb[0] = psk + 2 * lsk;
@ -183,8 +184,9 @@ vips_canny_nonmax_generate( VipsRegion *or,
for( band = 0; band < out_bands; band++ ) {
int G = p[lsk + psk];
int theta = p[lsk + psk + 1];
VipsPel low = p[offseta[theta]];
VipsPel high = p[offsetb[theta]];
int a = ((theta + 16) / 32) & 0x3;
VipsPel low = p[offseta[a]];
VipsPel high = p[offsetb[a]];
/* Set G to 0 if it's not the local maxima in
* the direction of the gradient. If G is equal
@ -230,6 +232,111 @@ vips_canny_nonmax( VipsImage *in, VipsImage **out )
return( 0 );
}
static int
vips_canny_nonmaxi_generate( VipsRegion *or,
void *vseq, void *a, void *b, gboolean *stop )
{
VipsRegion *in = (VipsRegion *) vseq;
VipsRect *r = &or->valid;
VipsImage *im = in->im;
int out_bands = or->im->Bands;
VipsRect rect;
int x, y, band;
int lsk;
int psk;
int offset[8];
rect = *r;
rect.width += 2;
rect.height += 2;
if( vips_region_prepare( in, &rect ) )
return( -1 );
lsk = VIPS_REGION_LSKIP( in );
psk = VIPS_IMAGE_SIZEOF_PEL( im );
/* For each of the 8 directions, the offset to get to that pixel from
* the top-left of the 3x3.
*
* 5 | 4 | 3
* --+---+--
* 6 | X | 2
* --+---+--
* 7 | 0 | 1
*/
offset[0] = psk + 2 * lsk;
offset[1] = 2 * psk + 2 * lsk;
offset[2] = 2 * psk + lsk;
offset[3] = 2 * psk;
offset[4] = psk;
offset[5] = 0;
offset[6] = lsk;
offset[7] = 2 * lsk;
for( y = 0; y < r->height; y++ ) {
VipsPel *p = (VipsPel * restrict)
VIPS_REGION_ADDR( in, r->left, r->top + y );
VipsPel *q = (VipsPel * restrict)
VIPS_REGION_ADDR( or, r->left, r->top + y );
for( x = 0; x < r->width; x++ ) {
for( band = 0; band < out_bands; band++ ) {
int G = p[lsk + psk];
int theta = p[lsk + psk + 1];
int low_theta = (theta / 32) & 0x7;
int high_theta = (low_theta + 1) & 0x7;
int residual = theta - low_theta * 32;
int lowa = p[offset[low_theta]];
int lowb = p[offset[high_theta]];
int low = (lowa * (32 - residual) +
lowb * residual) / 32;
int higha = p[offset[(low_theta + 4) & 0x7]];
int highb = p[offset[(high_theta + 4) & 0x7]];
int high = (higha * (32 - residual) +
highb * residual) / 32;
/* Set G to 0 if it's not the local maxima in
* the direction of the gradient.
*/
if( G <= low ||
G < high )
G = 0;
q[band] = G;
p += 2;
}
q += out_bands;
}
}
return( 0 );
}
/* Remove non-maximal edges. At each point, compare the G to the G in either
* direction and 0 it if it's not the largest.
*/
static int
vips_canny_nonmaxi( VipsImage *in, VipsImage **out )
{
*out = vips_image_new();
if( vips_image_pipelinev( *out,
VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
return( -1 );
(*out)->Bands /= 2;
(*out)->Xsize -= 2;
(*out)->Ysize -= 2;
if( vips_image_generate( *out,
vips_start_one, vips_canny_nonmaxi_generate, vips_stop_one,
in, NULL ) )
return( -1 );
return( 0 );
}
static int
vips_canny_build( VipsObject *object )
{
@ -292,7 +399,8 @@ vips_canny_build( VipsObject *object )
if( vips_embed( in, &t[10], 1, 1, in->Xsize + 2, in->Ysize + 2,
"extend", VIPS_EXTEND_COPY,
NULL ) ||
vips_canny_nonmax( t[10], &t[11] ) )
//vips_canny_nonmax( t[10], &t[11] ) )
vips_canny_nonmaxi( t[10], &t[11] ) )
return( -1 );
in = t[11];
@ -344,7 +452,7 @@ vips_canny_class_init( VipsCannyClass *class )
static void
vips_canny_init( VipsCanny *canny )
{
canny->sigma = 1.4;
canny->sigma = 1.5;
}
/**