OpenCV 3.1 convexityDefects 错误修正。

最新推荐文章于 2024-09-09 10:48:35 发布

lm111111

最新推荐文章于 2024-09-09 10:48:35 发布

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针对3.1版本中convexityDefects函数存在的凸缺陷检测错误进行了修复。问题在于循环内部未对变量j进行初始化，导致结果出现偏差。通过在循环开始前设置j等于当前凸包点hcurr，解决了该问题。

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3.1版本的convexityDefects 结果总是有错，没办法，只好看看源代码了。发现还真是有问题。

问题原因：在每次for(;;)循环开始前，没对变量 j 进行初始化。

修改为：在for(;;) 语句前加：j = hcurr;

其它版本是否有类似问题，大家可以找找看。

3.1版本的原码如下：

void convexityDefects( InputArray _points, InputArray _hull, OutputArray _defects )
{
Mat points = _points.getMat();
int i, j = 0, npoints = points.checkVector(2, CV_32S);
CV_Assert( npoints >= 0 );

if( npoints <= 3 )
{
_defects.release();
return;
}

Mat hull = _hull.getMat();
int hpoints = hull.checkVector(1, CV_32S);
CV_Assert( hpoints > 2 );

const Point* ptr = points.ptr<Point>();
const int* hptr = hull.ptr<int>();
std::vector<Vec4i> defects;

// 1. recognize co-orientation of the contour and its hull
bool rev_orientation = ((hptr[1] > hptr[0]) + (hptr[2] > hptr[1]) + (hptr[0] > hptr[2])) != 2;

// 2. cycle through points and hull, compute defects
int hcurr = hptr[rev_orientation ? 0 : hpoints-1];
CV_Assert( 0 <= hcurr && hcurr < npoints );

for( i = 0; i < hpoints; i++ )
{
int hnext = hptr[rev_orientation ? hpoints - i - 1 : i];
CV_Assert( 0 <= hnext && hnext < npoints );

Point pt0 = ptr[hcurr], pt1 = ptr[hnext];
double dx0 = pt1.x - pt0.x;
double dy0 = pt1.y - pt0.y;
double scale = dx0 == 0 && dy0 == 0 ? 0. : 1./std::sqrt(dx0*dx0 + dy0*dy0);

int defect_deepest_point = -1;
double defect_depth = 0;
bool is_defect = false;

for(;;)
{
// go through points to achieve next hull point
j++;
j &= j >= npoints ? 0 : -1;
if( j == hnext )
break;

// compute distance from current point to hull edge
double dx = ptr[j].x - pt0.x;
double dy = ptr[j].y - pt0.y;
double dist = fabs(-dy0*dx + dx0*dy) * scale;

if( dist > defect_depth )
{
defect_depth = dist;
defect_deepest_point = j;
is_defect = true;
}
}

if( is_defect )
{
int idepth = cvRound(defect_depth*256);
defects.push_back(Vec4i(hcurr, hnext, defect_deepest_point, idepth));
}

hcurr = hnext;
}

Mat(defects).copyTo(_defects);
}

修改完成以后，源代码为：

void convexityDefects( InputArray _points, InputArray _hull, OutputArray _defects )
{
Mat points = _points.getMat();
int i, j = 0, npoints = points.checkVector(2, CV_32S);
CV_Assert( npoints >= 0 );

if( npoints <= 3 )
{
_defects.release();
return;
}

Mat hull = _hull.getMat();
int hpoints = hull.checkVector(1, CV_32S);
CV_Assert( hpoints > 2 );

const Point* ptr = points.ptr<Point>();
const int* hptr = hull.ptr<int>();
std::vector<Vec4i> defects;

// 1. recognize co-orientation of the contour and its hull
bool rev_orientation = ((hptr[1] > hptr[0]) + (hptr[2] > hptr[1]) + (hptr[0] > hptr[2])) != 2;

// 2. cycle through points and hull, compute defects
int hcurr = hptr[rev_orientation ? 0 : hpoints-1];
CV_Assert( 0 <= hcurr && hcurr < npoints );

for( i = 0; i < hpoints; i++ )
{
int hnext = hptr[rev_orientation ? hpoints - i - 1 : i];
CV_Assert( 0 <= hnext && hnext < npoints );

Point pt0 = ptr[hcurr], pt1 = ptr[hnext];
double dx0 = pt1.x - pt0.x;
double dy0 = pt1.y - pt0.y;
double scale = dx0 == 0 && dy0 == 0 ? 0. : 1./std::sqrt(dx0*dx0 + dy0*dy0);

int defect_deepest_point = -1;
double defect_depth = 0;
bool is_defect = false;

j = hcurr;

for(;;)
{
// go through points to achieve next hull point
j++;
j &= j >= npoints ? 0 : -1;
if( j == hnext )
break;

// compute distance from current point to hull edge
double dx = ptr[j].x - pt0.x;
double dy = ptr[j].y - pt0.y;
double dist = fabs(-dy0*dx + dx0*dy) * scale;

if( dist > defect_depth )
{
defect_depth = dist;
defect_deepest_point = j;
is_defect = true;
}
}

if( is_defect )
{
int idepth = cvRound(defect_depth*256);
defects.push_back(Vec4i(hcurr, hnext, defect_deepest_point, idepth));
}

hcurr = hnext;
}

Mat(defects).copyTo(_defects);
}