在 OpenCV 的 findContours () 中使用层次结构?

问题描述

在查找轮廓时，我使用了 CV_RETR_CCOMP 参数.这应该创建一个两级层次结构 - 第一级用于外轮廓，第二级用于孔的边界.然而，我之前从未使用过层次结构，所以我对此并不熟悉.

When finding contours, I used the CV_RETR_CCOMP argument. This is supposed to create a two level hierarchy - the the first level are for outer contours, the second level are for boundaries of the holes. However, I have never used a hierarchy before so I am not familiar with this.

有人可以指导我如何仅访问孔的边界吗?我想忽略外部轮廓，只绘制孔边界.代码示例将不胜感激.我使用的是 C++ 接口而不是 C，所以请不要建议使用 C 函数(即使用 findContours () 而不是 cvFindContours ()).

Could someone instruct my on how to access the boundaries of the holes only? I want to disregard the outer contours and only draw the hole boundaries. Code examples will be appreciated. I am using the C++ interface not the C, so please don't suggest C functions (i.e. use findContours () instead of cvFindContours ()).

推荐答案

findContours 返回的层次结构具有以下形式:hierarchy[idx][{0,1,2,3}]={下一个轮廓(同级)，前一个轮廓(同级)，子轮廓，父轮廓}

The hierarchy returned by findContours has the following form: hierarchy[idx][{0,1,2,3}]={next contour (same level), previous contour (same level), child contour, parent contour}

CV_RETR_CCOMP，返回外部轮廓和孔的层次结构.这意味着 hierarchy[idx] 的元素 2 和 3 至多有一个不等于 -1:也就是说，每个元素要么没有父级或子级，要么有父级但没有子级，或者一个孩子，但没有父母.

CV_RETR_CCOMP, returns a hierarchy of outer contours and holes. This means elements 2 and 3 of hierarchy[idx] have at most one of these not equal to -1: that is, each element has either no parent or child, or a parent but no child, or a child but no parent.

具有父元素但没有子元素的元素将是孔的边界.

An element with a parent but no child would be a boundary of a hole.

这意味着您基本上要通过 hierarchy[idx] 并使用 hierarchy[idx][3]>-1 绘制任何内容.

That means you basically go through hierarchy[idx] and draw anything with hierarchy[idx][3]>-1.

类似的东西(在 Python 中工作，但还没有测试 C++.不过这个想法很好.):

Something like (works in Python, but haven't tested the C++. Idea is fine though.):

findContours( image, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );

if ( !contours.empty() && !hierarchy.empty() ) {

    // loop through the contours/hierarchy
    for ( int i=0; i<contours.size(); i++ ) {

        // look for hierarchy[i][3]!=-1, ie hole boundaries
        if ( hierarchy[i][3] != -1 ) {
            // random colour
            Scalar colour( (rand()&255), (rand()&255), (rand()&255) );
            drawContours( outImage, contours, i, colour );
        }
    }
}

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