python - opencv.groupRectangles() c++ 和 python 层之间的差异

Question

我正在尝试将对 opencv 的 groupRectangles() 的调用从 python 转换为 c++，并且注意到 python 绑定(bind)的输出与 c++ 调用的输出不匹配。

我编辑了下面的输出以反射(reflect)在 ubuntu 18.04 上使用 opencv 3.2 重现此内容

库版本

我在 Ubuntu 18.04 上运行 opencv。

c++ 程序链接到 opencv 3.2.0(由 ldd 报告)。

python 模块报告版本 3.2.0

C++代码

我编写了以下程序来获取一组 (x1, y1, x2, y2) 输入并将它们传递给组阈值为 3 且 epsilon 为 0.02 的 groupRectangles()。为了便于比较，输出以python的列表格式打印。

#include <opencv2/opencv.hpp>
#include <iostream>
#include <vector>

// display in python format
std::ostream& operator<<(std::ostream& out, std::vector<cv::Rect>& rectangles)
{
    out << '[';
    for (auto i = 0u; i<rectangles.size(); ++i)
    {
        if (i)
            out << ',';
        out << '[' << rectangles[i].tl().x << ',' << rectangles[i].tl().y << ',' << rectangles[i].br().x << ',' << rectangles[i].br().y << ']';
    }
    return out << ']';
}

// inputs are x1,y1,x2,y2
constexpr const float inputs[][4] = {{547,432,701,639},{557,435,700,640},{560,438,695,641},{560,438,694,640},{88,443,336,663},{83,444,357,671},{83,444,373,676},{87,449,377,676},{87,454,380,677},{76,453,388,680},{72,447,394,683},{80,437,393,683},{101,430,392,678},{547,433,702,641},{555,433,701,645},{558,437,696,647},{556,440,696,644},{84,443,357,664},{73,448,369,665},{74,449,375,664},{81,451,373,664},{85,454,375,666},{81,454,385,672},{74,452,392,676},{77,445,396,679},{91,433,392,680},{547,430,705,644},{553,429,704,649},{555,434,697,649},{552,438,695,649},{85,445,365,661},{69,451,376,662},{69,452,379,663},{76,453,374,663},{80,452,377,666},{79,451,382,671},{74,449,388,673},{77,445,393,673},{90,434,389,674},{546,429,706,643},{553,428,703,647},{554,432,695,649},{553,435,693,654},{81,445,370,663},{68,454,383,664},{67,455,388,664},{72,454,384,667},{77,452,382,669},{71,448,386,671},{66,443,388,672},{73,438,389,671},{92,429,388,673},{545,429,706,642},{553,429,703,643},{553,432,695,647},{553,432,696,658},{79,450,367,664},{72,459,379,663},{71,459,387,665},{75,458,388,667},{75,455,390,666},{65,448,389,668},{63,441,387,669},{73,433,384,672},{100,425,388,675},{549,429,707,648},{550,429,701,652},{554,434,703,662},{79,462,356,665},{73,462,374,665},{74,461,383,666},{73,460,387,667},{69,457,391,664},{60,447,390,668},{63,435,385,673},{81,430,384,676},{116,433,390,677}};

int main()
{
    std::vector<cv::Rect> candidates;
    std::transform(std::begin(inputs), std::end(inputs), std::back_inserter(candidates),
        [](const float coord[4]) {
            return cv::Rect(cv::Point((int)coord[0], (int)coord[1]), cv::Point((int)coord[2], (int)coord[3]));
         });

    std::cout << "input:\n" << candidates << '\n';
    std::vector<int> weights(candidates.size());
    cv::groupRectangles(candidates, weights, 3, 0.02); 
    std::cout << "output:\n" << candidates << '\n';

    return EXIT_SUCCESS;
}

测试执行

当执行 c++ 程序时，我得到以下输出:

input:
[[547,432,701,639],[557,435,700,640],[560,438,695,641],[560,438,694,640],[88,443,336,663],[83,444,357,671],[83,444,373,676],[87,449,377,676],[87,454,380,677],[76,453,388,680],[72,447,394,683],[80,437,393,683],[101,430,392,678],[547,433,702,641],[555,433,701,645],[558,437,696,647],[556,440,696,644],[84,443,357,664],[73,448,369,665],[74,449,375,664],[81,451,373,664],[85,454,375,666],[81,454,385,672],[74,452,392,676],[77,445,396,679],[91,433,392,680],[547,430,705,644],[553,429,704,649],[555,434,697,649],[552,438,695,649],[85,445,365,661],[69,451,376,662],[69,452,379,663],[76,453,374,663],[80,452,377,666],[79,451,382,671],[74,449,388,673],[77,445,393,673],[90,434,389,674],[546,429,706,643],[553,428,703,647],[554,432,695,649],[553,435,693,654],[81,445,370,663],[68,454,383,664],[67,455,388,664],[72,454,384,667],[77,452,382,669],[71,448,386,671],[66,443,388,672],[73,438,389,671],[92,429,388,673],[545,429,706,642],[553,429,703,643],[553,432,695,647],[553,432,696,658],[79,450,367,664],[72,459,379,663],[71,459,387,665],[75,458,388,667],[75,455,390,666],[65,448,389,668],[63,441,387,669],[73,433,384,672],[100,425,388,675],[549,429,707,648],[550,429,701,652],[554,434,703,662],[79,462,356,665],[73,462,374,665],[74,461,383,666],[73,460,387,667],[69,457,391,664],[60,447,390,668],[63,435,385,673],[81,430,384,676],[116,433,390,677]]
output:
[[546,431,704,642],[70,447,389,672],[555,435,696,647],[74,455,381,666]]

在 python 中，我将 c++ 输入剪切并粘贴为 groupRectangles() 的输入，但得到完全不同的结果:

cv2.groupRectangles([[547,432,701,639],[557,435,700,640],[560,438,695,641],[560,438,694,640],[88,443,336,663],[83,444,357,671],[83,444,373,676],[87,449,377,676],[87,454,380,677],[76,453,388,680],[72,447,394,683],[80,437,393,683],[101,430,392,678],[547,433,702,641],[555,433,701,645],[558,437,696,647],[556,440,696,644],[84,443,357,664],[73,448,369,665],[74,449,375,664],[81,451,373,664],[85,454,375,666],[81,454,385,672],[74,452,392,676],[77,445,396,679],[91,433,392,680],[547,430,705,644],[553,429,704,649],[555,434,697,649],[552,438,695,649],[85,445,365,661],[69,451,376,662],[69,452,379,663],[76,453,374,663],[80,452,377,666],[79,451,382,671],[74,449,388,673],[77,445,393,673],[90,434,389,674],[546,429,706,643],[553,428,703,647],[554,432,695,649],[553,435,693,654],[81,445,370,663],[68,454,383,664],[67,455,388,664],[72,454,384,667],[77,452,382,669],[71,448,386,671],[66,443,388,672],[73,438,389,671],[92,429,388,673],[545,429,706,642],[553,429,703,643],[553,432,695,647],[553,432,696,658],[79,450,367,664],[72,459,379,663],[71,459,387,665],[75,458,388,667],[75,455,390,666],[65,448,389,668],[63,441,387,669],[73,433,384,672],[100,425,388,675],[549,429,707,648],[550,429,701,652],[554,434,703,662],[79,462,356,665],[73,462,374,665],[74,461,383,666],[73,460,387,667],[69,457,391,664],[60,447,390,668],[63,435,385,673],[81,430,384,676],[116,433,390,677]], 3, 0.02)
(array([[553, 433, 700, 647],
       [ 75, 449, 382, 669],
       [ 95, 430, 390, 676]], dtype=int32), array([[23],
       [46],
       [ 5]], dtype=int32))

这是我转换为 cv::Rect 的问题，groupRectangles() 中的非确定性或其他问题吗？

Answer 1

上面的问题完全在python <-> c++ cv::Rect 转换上。在 python 中，list[4] 是 x, y, height, width，not x1, y1, x2, y2(正如我被移植的代码中的错误所误导的那样)。

如果我更改以下行，上面的代码将正常工作。

打印时:

out << '[' << rectangles[i].tl().x << ',' << rectangles[i].tl().y << ',' << rectangles[i].width << ',' << rectangles[i].height << ']';

在构建 cv::Rect 时:

return cv::Rect((int)coord[0], (int)coord[1], (int)coord[2], (int)coord[3]);