function [result]=convexityDefects(ptr,hptr,image)
%获取图像的高和宽，通道
[rows,cols,channels]=size(image);
%获取轮廓的点数
npoints=length(ptr);
%获取凸包的点数
hpoints=length(hptr);
%检测到的结果，第一列为凸缺陷的开始点，第二个为凸缺陷的结束点，第三个为凸缺陷的凹点，第四个为凹点距离开始和结束线的距离
defects=zeros(hpoints,4);
%只有轮廓点数大于3时，才进行下去
if npoints>3
num=1;
hcurr=hptr(1);
％判断凸包点集的顺序
if ((hptr(2) > hptr(1)) + (hptr(3) > hptr(2)) + (hptr(1) > hptr(3))) ~= 2
rev_orientation=1;
else
rev_orientation=0;
end
%当凸包点集为顺序时，则从第一个凸包点开始遍历
if rev_orientation==1
hcurr=hptr(1);
%当凸包点集为逆序时，则从最后一个凸包点开始遍历
else
hcurr=hptr(hpoints);
end
％开始遍历凸包点
for i = 1:hpoints
%下一个凸包点
hnext=hptr(hpoints-i+1);
%当凸包点集为顺序时，则下一个凸包点是从尾开始
if rev_orientation==1
hnext=hptr(hpoints-i+1);
%当凸包点集为逆序时，则下一个凸包点是从头开始
else
hnext=hptr(i);
end
%计算这两个凸包点的x和y的距离，和直线距离为1/scale
pt0 = ptr(hcurr,:);
pt1 = ptr(hnext,:);
dx0 = pt1(2) - pt0(2);
dy0 = pt1(1) - pt0(1);
scale=0.0;
if dx0 == 0 && dy0 == 0
scale=0.0;
else
scale=1./sqrt(dx0*dx0 + dy0*dy0);
end
%凹点的下标
defect_deepest_point = -1;
%凸缺陷的深度
defect_depth = 0;
%判断是否检测到凸缺陷的标志位
is_defect = 0;
%遍历轮廓点
j=hcurr;
while(1)
j=j+1;
tempj=0;
%如果大于了轮廓点数，则从头遍历
if j>npoints
j=1;
% else
% tempj=-1;
end
% j =j & tempj;
%当j等于下一个凸包点时，则跳出
if j == hnext
break;
end
%计算凹点和凸包起始点的x和y距离
dx = ptr(j,2) - pt0(2);
dy = ptr(j,1) - pt0(1);
dist = abs(-dy0*dx + dx0*dy) * scale;
%存储最大的深度，和对应的凹点
if dist > defect_depth
defect_depth = dist;
defect_deepest_point = j;
is_defect = true;
end
end
%如果检测到凸缺陷，则加入检测结果
if is_defect
idepth = round(defect_depth*256);
defects(num,1)=hcurr;
defects(num,2)=hnext;
defects(num,3)=defect_deepest_point;
defects(num,4)=idepth;
num=num+1;
end
hcurr = hnext;
end
end
resultMum=0;
figure(5), imshow(image), title('original image');
hold on;
%筛选，筛选条件为当凸缺陷的深度>20且<200时，并且凸包点不在图像边缘时，则为手指尖点
for i=1:length(defects)
dist=defects(i,4)/256;
if defects(i,1)~=0 && defects(i,2)~=0 && dist>20 && dist<200 && ptr(defects(i,1),1)>3 && ptr(defects(i,1),1)<(cols-3) && ptr(defects(i,1),2)>3 && ptr(defects(i,1),2)<(rows-3)
resultMum=resultMum+1;
end
end
%将结果通过result返回，并显示
resultCount=1;
result=zeros(resultMum,2);
for i=1:length(defects)
dist=defects(i,4)/256;
if defects(i,1)~=0 && defects(i,2)~=0 && dist>20 && dist<200 && ptr(defects(i,1),1)>3 && ptr(defects(i,1),1)<(cols-3) && ptr(defects(i,1),2)>3 && ptr(defects(i,1),2)<(rows-3)
result(resultCount,1)=ptr(defects(i,1),1);
result(resultCount,2)=ptr(defects(i,1),2);
resultCount=resultCount+1;
plot(ptr(defects(i,1),1),ptr(defects(i,1),2),'.','markersize',30);
end
end
