OpenCV - 使用C ++从图像中裁剪非矩形区域 [英] OpenCV - Cropping non rectangular region from image using C++

问题描述

如何从图像裁剪非矩形区域？

How can I crop a non rectangular region from image?

想象一下，我有四个点，我想裁剪它，这个形状不会是一个三角形！

Imagine I have four points and I want to crop it, this shape wouldn't be a triangle somehow!

例如我有以下图片：

我想从图像中裁剪出来：

and I want to crop this from image :

我该怎么做？
问候..

How can I do this? regards..

推荐答案

裁剪任意四边形（或任何多边形）部分的过程image总结为：

The procedure for cropping an arbitrary quadrilateral (or any polygon for that matter) part of an image is summed us as:

• 生成掩码。你想要保留图像的面具是黑色，而你不想保留它的是白色。


• 计算输入图像和面具之间的bitwise_and

因此，我们假设你有一张图片。在整个过程中，为了简单起见，我将使用30x30的图像大小，您可以根据您的使用情况进行更改。

So, lets assume you have an image. Throughout this I'll use an image size of 30x30 for simplicity, you can change this to suit your use case.

cv::Mat source_image = cv::imread("filename.txt");

你有4个点想要用作角落：

And you have four points you want to use as the corners:

cv::Point corners[1][4];
corners[0][0] = Point( 10, 10 );
corners[0][1] = Point( 20, 20 );
corners[0][2] = Point( 30, 10 );
corners[0][3] = Point( 20, 10 );
const Point* corner_list[1] = { corners[0] };

您可以使用函数 cv :: fillPoly 在蒙版上绘制此形状：

You can use the function cv::fillPoly to draw this shape on a mask:

int num_points = 4;
int num_polygons = 1;
int line_type = 8;
cv::Mat mask(30,30,CV_8UC3, cv::Scalar(0,0,0));
cv::fillPoly( mask, corner_list, &num_points, num_polygons, cv::Scalar( 255, 255, 255 ),  line_type);

然后只需计算图像的bitwise_and并屏蔽：

Then simply compute the bitwise_and of the image and mask:

cv::Mat result;
cv::bitwise_and(source_image, mask, result);

结果现在有裁剪的图像。如果你想让边缘变成白色而不是黑色，你可以改为：

result now has the cropped image in it. If you want the edges to end up white instead of black you could instead do:

cv::Mat result_white(30,30,CV_8UC3, cv::Scalar(255,255,255));
cv::bitwise_and(source_image, mask, result_white, mask);

在这种情况下，我们使用 bitwise_and 's mask参数只能执行掩码中的bitwise_and。有关更多信息和所有链接，请参见本教程。我提到的功能。

In this case we use bitwise_and's mask parameter to only do the bitwise_and inside the mask. See this tutorial for more information and links to all the functions I mentioned.

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