用opencvSharp实现在任意多边形内寻找最大的内接正交矩形
之前写过一篇在任意多边形内寻找近似最大的内接正交矩形,但不怎么符合工作要求,于是再认真看了看之前那篇文章,最后总算是搞出来了。
原图:
结果:
1.第一步还是先求出多边形的近似轮廓,减少轮廓数量,方便后面计算。
2.根据轮廓画出所有点与点之间依次相连的矩形,比如一个有4个轮廓点,那就用第1个点和第2个点组成一个矩形,第1个和第3个组成,第1个和第4个,第2个和第3个,第2个和第4个,第3个和第4个。
//根据轮廓画出所有点与点之间依次相连的矩形
List<Rect> allRect = new List<Rect>();
for (int i = 0; i < contour.Count; i++)
{
for (int j = i + 1; j < contour.Count; j++)
{
var p1 = contour[i];
var p2 = contour[j];
if (Math.Abs(p1.Y - p2.Y) < 3 || Math.Abs(p1.X - p2.X) < 3)
continue;
var temp = FromTowPoint(p1, p2);
allRect.Add(temp);
//src.Rectangle(temp, Scalar.RandomColor());
}
}
3.在所有矩形中求出两两相交的矩形,把符合条件的相交矩形当作内部矩形。条件如下:非空和非重复的矩形;只要矩形包含一个轮廓内的点,就不算多边形的内部矩形;只要轮廓不包含该矩形,该矩形就不算多边形的内部矩形。
List<Rect> insideRects = new List<Rect>();
for (int i = 0; i < allRect.Count; i++)
{
for (int j = i + 1; j < allRect.Count; j++)
{
var r1 = allRect[i];
var r2 = allRect[j];
//在所有矩形中求出相交的矩形,把符合条件的相交矩形当作内部矩形
var r3 = r1.Intersect(r2);
if (r3.Width == 0 || r3.Height == 0
|| ContainsAnyPt(r3, contour) //只要矩形包含一个轮廓内的点,就不算多边形的内部矩形
|| !ContainPoints(contour, GetAllCorner(r3)) //只要轮廓不包含该矩形,该矩形就不算多边形的内部矩形
|| insideRects.Contains(r3))
continue;
src.Rectangle(r3, Scalar.RandomColor(), 1);
insideRects.Add(r3);
}
}
4.两两组合所有内部矩形,排除不符合条件的,然后面积最大的就是最大内接矩形。
比如最后只剩3个内部矩形,那就用第1个的左上角坐标和第2个的右下角坐标,组成一个新的矩形,先看新矩形是否依然是内部矩形,如果是则计算其面积,与最大面积比较,看看哪个大;然后同样的流程处理第1个和第3个,第2个第3个内部矩形。
//组合所有内部矩形,面积最大的就是最大内接矩形
for (int i = 0; i < insideRects.Count; i++)
{
for (int j = i + 1; j < insideRects.Count; j++)
{
var r1 = insideRects[i];
var r2 = insideRects[j];
var newRect = FromTowPoint(r1.Location, r2.BottomRight);
if (ContainsAnyPt(newRect, contour) || !ContainPoints(contour, GetAllCorner(newRect)))
continue;
if(newRect.Width * newRect.Height > maxInscribedRect.Width * maxInscribedRect.Height)
maxInscribedRect = newRect;
}
以上就是所有步骤了,代码实现起来还是比较简单的,但是这个方法的原理理解起来就比较困难了。
完整代码:
public Form1()
{
InitializeComponent();
Test();
}
private static void Test()
{
var src = Cv2.ImRead("C:\\Users\\Administrator\\Desktop\\test.png", ImreadModes.Color);
var dst = new Mat();
Cv2.CvtColor(src, dst, ColorConversionCodes.RGB2GRAY);
Cv2.FindContours(dst, out var contours, out var hierarchy, RetrievalModes.External,
ContourApproximationModes.ApproxSimple);
List<List<Point>> approxContours = new List<List<Point>>();
for (int i = 0; i < contours.Length; i++)
{
//先求出多边形的近似轮廓,减少轮廓数量,方便后面计算
var approxContour = Cv2.ApproxPolyDP(contours[i], 15, true);
approxContours.Add(approxContour.ToList());
DrawContour(src, approxContour, Scalar.White, 1);
}
foreach (var contour in approxContours)
{
GetMaxInscribedRect(src, contour);
}
Cv2.ImShow("src", src);
}
private static Rect GetMaxInscribedRect(Mat src, List<Point> contour)
{
Rect maxInscribedRect = new Rect();
//根据轮廓画出所有点与点之间依次相连的矩形
List<Rect> allRect = new List<Rect>();
for (int i = 0; i < contour.Count; i++)
{
for (int j = i + 1; j < contour.Count; j++)
{
var p1 = contour[i];
var p2 = contour[j];
if (Math.Abs(p1.Y - p2.Y) < 3 || Math.Abs(p1.X - p2.X) < 3)
continue;
var temp = FromTowPoint(p1, p2);
allRect.Add(temp);
//src.Rectangle(temp, Scalar.RandomColor());
}
}
//在所有矩形中找出多边形内部矩形
List<Rect> insideRects = new List<Rect>();
for (int i = 0; i < allRect.Count; i++)
{
for (int j = i + 1; j < allRect.Count; j++)
{
var r1 = allRect[i];
var r2 = allRect[j];
var r3 = r1.Intersect(r2);
if (r3.Width == 0 || r3.Height == 0
|| ContainsAnyPt(r3, contour) //只要矩形包含一个轮廓内的点,就不算多边形的内部矩形
|| !ContainPoints(contour, GetAllCorner(r3)) //只要轮廓不包含该矩形,该矩形就不算多边形的内部矩形
|| insideRects.Contains(r3))
continue;
src.Rectangle(r3, Scalar.RandomColor(), 1);
insideRects.Add(r3);
}
}
//组合所有内部矩形,面积最大的就是最大内接矩形
for (int i = 0; i < insideRects.Count; i++)
{
for (int j = i + 1; j < insideRects.Count; j++)
{
var r1 = insideRects[i];
var r2 = insideRects[j];
var newRect = FromTowPoint(r1.Location, r2.BottomRight);
if (ContainsAnyPt(newRect, contour) || !ContainPoints(contour, GetAllCorner(newRect)))
continue;
if(newRect.Width * newRect.Height > maxInscribedRect.Width * maxInscribedRect.Height)
maxInscribedRect = newRect;
}
}
if(insideRects.Count == 1)
maxInscribedRect = insideRects[0];
src.Rectangle(maxInscribedRect, Scalar.Yellow, 2);
return maxInscribedRect;
}
private static Point[] GetAllCorner(Rect rect)
{
Point[] result = new Point[4];
result[0] = rect.Location;
result[1] = new Point(rect.X + rect.Width, rect.Y);
result[2] = rect.BottomRight;
result[3] = new Point(rect.X, rect.Y + rect.Height);
return result;
}
private static bool ContainPoints(List<Point> contour, IEnumerable<Point> points)
{
foreach (var point in points)
{
if (Cv2.PointPolygonTest(contour, point, false) < 0)
return false;
}
return true;
}
private static void DrawContour(Mat mat, Point[] contour, Scalar color, int thickness)
{
for (int i = 0; i < contour.Length; i++)
{
if (i + 1 < contour.Length)
Cv2.Line(mat, contour[i], contour[i + 1], color, thickness);
}
}
/// <summary>
/// 是否有任意一个点集合中的点包含在矩形内,在矩形边界上不算包含
/// </summary>
/// <param name="rect"></param>
/// <param name="points"></param>
/// <returns></returns>
private static bool ContainsAnyPt(Rect rect, IEnumerable<Point> points)
{
foreach (var point in points)
{
if (point.X > rect.X && point.X < rect.X + rect.Width && point.Y < rect.BottomRight.Y && point.Y > rect.Y)
return true;
}
return false;
}
/// <summary>
/// 用任意两点组成一个矩形
/// </summary>
/// <param name="p1"></param>
/// <param name="p2"></param>
/// <returns></returns>
public static Rect FromTowPoint(Point p1, Point p2)
{
if (p1.X == p2.X || p1.Y == p2.Y)
return Rect.Empty;
if (p1.X > p2.X && p1.Y < p2.Y)
{
(p1, p2) = (p2, p1);
}
else if (p1.X > p2.X && p1.Y > p2.Y)
{
(p1.X, p2.X) = (p2.X, p1.X);
}
else if (p1.X < p2.X && p1.Y < p2.Y)
{
(p1.Y, p2.Y) = (p2.Y, p1.Y);
}
return Rect.FromLTRB(p1.X, p2.Y, p2.X, p1.Y);
}