如何确定OpenCV轮廓中的曲线点 [英] How to determine curve points in OpenCV contours

问题描述

大家好，



对于我的图像处理项目，我需要在轮廓中找到曲线点。



在下面显示的示例图像中，检测到的轮廓以红色显示。现在我需要在水平和/或垂直轴上找到曲线点/坐标（用蓝色箭头表示）。



http://imageshack.com/a/img540/7162/3NEzhC.jpg [ ^ ]



曲线未必完美省略号。



任何人都可以告诉我这样做的好方法。

一些参考代码块会非常感激，但会有一个解释单独也会有所帮助。

Hello everyone,

For my image processing project i need to find curve points in a contour.

In the example image shown below, detected contour is shown in Red. Now i need to find the curve points/coordinates (indicated with blue arrows) on horizontal and/or vertical axis.

http://imageshack.com/a/img540/7162/3NEzhC.jpg[^]

The curves may not necessarily be perfect ellipses.

Can anyone please let me know a good approach to do so.
Some reference code block would be much appreciated but an explanation alone would also be helpful.

推荐答案

Hello Everyone

Hello Everyone

我研究了一下，发现取轮廓的一阶导数（分别用于x和y）可以解决这个问题。

I studied a bit and found that taking the first order derivative of the contour (for x and for y separately) can solve this problem.

一阶导数用于找到局部最大值和最小值。在曲线点上，一阶导数的值从正变为负（对于峰值）和从负变为正（对于谷）。

The first order derivative is used to find Local Maxima and Minima. On the curve points the value of the first order derivative changes from positive to negative (for a peak) and from negative to positive (for a valley).

基本定义一维函数f（x）的一阶导数是差值

A basic definition of the first-order derivative of a one-dimensional function f(x) is the difference

df / dx = f（x + 1） - f（x）

要确定波谷和峰值（水平轴上的曲线点），只需要轮廓点的Y值。类似于确定垂直轴上的曲线点，只需要轮廓点的X值。

To determine valley and peaks (curve points on horizontal axis), only Y value of the contour points is required. Similarly to determine curve points on vertical axis, only X value of the contour points is required.

我在这里放了一小部分用于确定山谷的代码（Minima）在轮廓中。

I am putting here a small part of code used to determine only valleys (Minima) in a contour.

非常欢迎任何改进方法或代码的建议。

Any suggestion to improve the approach or the code is very much welcome.

int posCntr = 0;
int negCntr = 0;
var diffY = new List<List<int>>();
var diff2Y = new List<List<int>>();
var diffSeq = new List<List<int>>();
// Process each detected contour
for (int n = 0; n < validContours.Count; n++)
{
    posCntr = 0;
    negCntr = 0;
    diffY.Add(new List<int>());
    diffSeq.Add(new List<int>());
    for (int i = 0; i < validContours[n].Total - 1; i++)
    {
        // Taking first derivative of contour
        // df/dy = f(y+1) - f(y);
        diffY[n].Add(validContours[n][i + 1].Y - validContours[n][i].Y);
        // count continuous positive and negative values and add them to a list
        // list will have consecutive positives, negatives, positives, negatives, ...
        if (diffY[n][i] >= 0)
        {
            posCntr++;
            if (negCntr != 0)
            {
                diffSeq[n].Add(negCntr);
                negCntr = 0;
            }
        }
        else //if (diffY[n][i] < 0)
        {
            negCntr++;
            if (posCntr != 0)
            {
                diffSeq[n].Add(posCntr);
                posCntr = 0;
            }
        }
    }
    if (negCntr != 0)
    {
        diffSeq[n].Add(negCntr);
        negCntr = 0;
    }
    else if (posCntr != 0)
    {
        diffSeq[n].Add(posCntr);
        posCntr = 0;
    }
}
int cntr;
for (int n = 0; n < validContours.Count; n++)
{
    cntr = 0;
    for (int i = 0; i < diffSeq[n].Count - 1; i = i + 2)
    {
        // Check if the consequtive pos, neg seq counts are above a threshold level
        // if they are, means we have found a Minima
        if (diffSeq[n][i]     >= Constants.CURVE_SZ && 
            diffSeq[n][i + 1] >= Constants.CURVE_SZ)
            Console.WriteLine(validContours[n][cntr + diffSeq[n][i]].ToString());
        cntr += diffSeq[n][i] + diffSeq[n][i+1];
    }
}

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