OpenCV，从图像围绕对象绘制一个框 [英] Opencv, drawing a box around an object from an image
问题描述
我正在做一个有趣的项目，以了解有关OpenCV的更多信息.此刻，我想画一个给定图像的盒子.我有一个可以完成这项工作的功能，但是在将mouse_control函数传递给OpenCV的setMouseCallback函数时遇到了一些问题.
I am doing a project for fun to learn more about OpenCV. At the moment I want to draw a box given an image. I have a working function that achieves the job but I am having some problem regarding passing the mouse_control function into the setMouseCallback function from OpenCV.
我收到的错误是这样的:
The error I am receiving is this:
error C3867: 'Box::mouse_control': non-standard syntax; use '&' to create a pointer to member
当我尝试放置建议的参考文献时，出现此错误:
When I try to place the suggested reference I get this error:
error C2276: '&': illegal operation on bound member function expression
我是OpenCV的新手，所以我不确定如何调试和修复我的代码.
I am brand new to OpenCV so I am not sure exactly how to debug and fix the code I have.
这是我正在处理的类的头文件:
Here is the header file to the class I am working on:
#pragma once
#include "Image.h"
class Box : public Image
{
public:
Box() = default;
Mat draw_box(Mat& img, Rect box);
void mouse_control(int event, int x, int y, int flag, void* param);
private:
Rect g_rectangle;
bool g_drawbox;
};
这是与头文件关联的.cpp文件:
Here is the .cpp file associated to the header file:
#include "Box.h"
#define WINDOW_NAME "Drawing Rectangle"
void Box::mouse_control(int event, int x, int y, int flag, void* param)
{
Mat& image = *(cv::Mat*) param;
switch (event)
{
case EVENT_MOUSEMOVE:
{ // When mouse moves, get the current rectangle's width and height
if (g_drawbox)
{
g_rectangle.width = x - g_rectangle.x;
g_rectangle.height = y - g_rectangle.y;
}
}
break;
case EVENT_LBUTTONDOWN:
{ // when the left mouse button is pressed down,
// get the starting corner's coordinates of the rectangle
g_drawbox = true;
g_rectangle = Rect(x, y, 0, 0);
}
break;
case EVENT_LBUTTONUP:
{ // when the left mouse button is released,
// draw the rectangle
g_drawbox = false;
if (g_rectangle.width < 0)
{
g_rectangle.x += g_rectangle.width;
g_rectangle.width *= -1;
}
if (g_rectangle.height < 0)
{
g_rectangle.y += g_rectangle.height;
g_rectangle.height *= -1;
}
draw_box(image, g_rectangle);
}
break;
}
}
Mat Box::draw_box(Mat& img, Rect box)
{
// Get input from user to draw box around object of interest
rectangle(img, box.tl(), box.br(), Scalar(0, 255, 255), FILLED, LINE_8);
Mat tempImage;
//Mat srcImage(600, 800, CV_8UC3);
//srcImage = Scalar::all(0);
namedWindow(WINDOW_NAME);
setMouseCallback(WINDOW_NAME, mouse_control, (void*)& img);
while (1) {
img.copyTo(tempImage);
if (g_drawbox)
draw_box(tempImage, g_rectangle);
imshow(WINDOW_NAME, tempImage);
if (waitKey(10) == 27) // stop drawing rectanglge if the key is 'ESC'
break;
}
return img;
}
错误发生在这里:
setMouseCallback(WINDOW_NAME, mouse_control, (void*)& img);
这里是主文件，另一个标头和cpp文件需要复制错误:
Here is the main file and the other header and cpp file needed to duplicate the error:
#include <iostream>
#include "Box.h"
#include "Image.h"
int main()
{
// Declare image object and the name of the image (store image in project file)
Image img_obj;
std::string image_name = "hawaii.png";
// Read and display image
auto img1 = img_obj.get_image(image_name);
img_obj.display(img1);
Rect g_rectangle;
Box b;
auto new_img = b.draw_box(img1, g_rectangle);
b.display(new_img);
std::cin.get();
}
#pragma once
#include <opencv2/opencv.hpp>
using namespace cv;
class Image
{
public:
Image() = default;
// Member functions
const Mat get_image(std::string& image_name);
void display(Mat& img);
};
#include "Image.h"
const Mat Image::get_image(std::string& image_name)
{
Mat img = imread(image_name);
return img;
}
void Image::display(Mat& img)
{
namedWindow("image", WINDOW_NORMAL);
imshow("image", img);
waitKey(0);
}
推荐答案
成员函数和 normal 函数是两个不同的东西.
Member function and normal function are two different things.
setMouseCallback函数采用签名为:
handleMouse(int event, int x, int y, int flag, void* param)
您尝试通过mouse_control作为回调来调用setMouseCallback，但由于mouse_control是Box类的成员函数，因此无法正常工作.您调用特定对象的成员函数，就不能将其称为独立"-没有对象.这就是为什么您的代码无法编译的原因.
you try to call setMouseCallback passing mouse_control as callback, it cannot work because mouse_control is member function of Box class. You call member function for particular object, you cannot call it "standalone" - without object. That is why your code doesn't compile.
解决方案?
回调的最后一个参数是void*.现在，您正在将指针传递给Image，但是您可以将指针传递给Box，不是吗?因此，您可以将mouse_control设置为Box类的静态函数:
The last param of callback is void*. Now, you are passing pointer to Image, but you can pass pointer to Box, isn't it? So, you can make mouse_control as static function of Box class:
class Box : public Image {
public:
Box() = default;
Mat draw_box(Mat& img, Rect box);
static void mouse_control(int event, int x, int y, int flag, void* param); // static added
(静态函数不需要具有要调用的对象). 您可以通过调用以下内容来指向该指针:
(static function doesn't need to have an object to be called). Pointer to this you pass by calling:
setMouseCallback(WINDOW_NAME, mouse_control, this);
和内部:
void Box::mouse_control(int event, int x, int y, int flag, void* param) {
Box* box = (Box*)param;
// you can access member variable of Box by
box->g_rectangle
box->draw_box
还需要找出如何存储img的方法，也许是作为Box的数据成员吗?或者，您可以制作一些包装器
also you need to find out how to store img, maybe as data member of Box?. Or you can make some wrapper like
struct Foo {
Box* box;
Image img;
};
，并将指向此结构的指针作为回调的最后一个参数.
and pass pointer to this struct as the last parameter of your callback.
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