Some thoughts on whether the judgment point is located in the contour

stay CSDN We found a method to judge whether the point is inside the polygon , Links are as follows ：
https://blog.csdn.net/u011722133/article/details/52813374
https://blog.csdn.net/hjk61314/article/details/82587196

Then can we use the above method to judge whether the point is within the contour ？
The answer is ： have to (děi) Sub situation .
When the width of our outline is 1 when , Sure , But when the outline width is not 1 Time is not allowed .

For example, the following outline is ok ：

But the following outline is not allowed ：

Why not? , Why you can , According to the methods provided in the above two blog posts, it is easy to think .

In fact, when the width is 1 when , You can use functions drawContours() Draw the outline point set in a solid way ( Parameters thickness The value of the set FILLED). Then judge whether a point is inside the contour .
When the outline is drawn in a solid way , For example, the following is drawn as a solid outline ：

I just need to judge whether the pixel gray value at a certain point is greater than a certain threshold , For example, judge whether the gray value of the pixel is greater than 200. Greater than 200 It is thought to be on or inside the contour , Less than 200 It is thought to be outside the contour .