template <class P> static
StarDetector::Status Detect( DPoint& pos, int& radius, float threshold, const GenericImage<P>& img )
{
img.Status().DisableInitialization();
/*
* Iteratively find the barycenter of a star.
*/
for ( int it = 0; it < 10; ++it )
{
// Central pixel in the current search box
Point p0 = pos;
// Search box
Rect r0( p0-radius, p0+radius+1 );
if ( !img.Intersects( r0 ) )
return StarDetector::OutsideImage;
// Extract the search subimage
img.SelectRectangle( r0 );
r0 = img.SelectedRectangle(); // in case the search box is clipped
Image simg( img );
// Threshold background pixels
Threshold( simg, threshold );
// Begin searching from the brightest pixel
if ( simg.LocateMaximumPixelValue( p0 ) == simg.MinimumPixelValue() )
return StarDetector::NoSignificantData;
// Coordinate and intensity accumulators.
double sx = 0, sy = 0, si = 0;
// Star bounding rectangle.
Rect r( p0, p0 );
for ( int down = 0; down < 2; ++down )
{
if ( down ? (p0.y == simg.Height()-1) : (p0.y == 0) )
continue;
for ( int y = down ? p0.y+1 : p0.y; ; )
{
double yc = y + 0.5;
int xa, xb;
/*
* Explore the left segment of this row.
*/
for ( xa = p0.x+1; xa > 0; )
{
Image::sample f = simg.Pixel( xa-1, y );
if ( f == 0 )
break;
--xa;
sx += f*(xa + 0.5);
sy += f*yc;
si += f;
}
/*
* Explore the right segment of this row.
*/
for ( xb = p0.x; xb < simg.Width()-1; )
{
Image::sample f = simg.Pixel( xb+1, y );
if ( f == 0 )
break;
++xb;
sx += f*(xb + 0.5);
sy += f*yc;
si += f;
}
/*
* Update horizontal boundaries.
*/
if ( xa < r.x0 ) // left boundary
r.x0 = xa;
if ( xb >= r.x1 ) // right boundary
r.x1 = xb+1;
/*
* Update y to explore the next row.
*/
if ( down )
{
++y;
if ( y == simg.Height() )
break;
}
else
{
if ( y == 0 )
break;
--y;
}
/*
* Decide whether we are done with this star, or if there is at
* least one more row that has to be explored. This is true if
* there is at least one significant pixel touching the current row
* in the next row.
*/
bool nextRow = false;
for ( int x = xa; x <= xb; ++x )
if ( simg.Pixel( x, y ) != 0 )
{
nextRow = true;
break;
}
if ( !nextRow )
break;
/*
* Update vertical boundaries.
*/
if ( down )
r.y1 = y+1; // bottom boundary
else
r.y0 = y; // top boundary
}
}
/*
* Check if we have gathered some data.
*/
if ( 1 + si == 1 )
return StarDetector::NoSignificantData;
/*
* Update barycenter coordinates.
*/
DPoint lastPos = pos;
pos.x = r0.x0 + sx/si;
pos.y = r0.y0 + sy/si;
/*
* Update search radius.
*/
int r1 = Range( Max( r.Width(), r.Height() ), 5, 127 );
if ( r1 != radius )
radius = r1;
else
{
/*
* If the search radius has stabilized, check if we have reached
* convergence. We converge to within +/- 0.01 px.
*/
if ( Abs( pos.x - lastPos.x ) < 0.005 && Abs( pos.y - lastPos.y ) < 0.005 )
return (r.x0 > 0 && r.y0 > 0 && r.x1 < simg.Width() && r.y1 < simg.Height()) ?
StarDetector::DetectedOk : StarDetector::CrossingEdges;
}
}
return StarDetector::NoConvergence;
}
