为什么openCV中的输入图像findContours()要转灰度？

Question

我正在关注以下站点上的教程：

http://harismoonamkunnu.blogspot.co.uk/2013/06/opencv-find-biggest-contour-using-c.html

如果我遵循代码，它会完美运行。但是，我所做的是输入一个灰度图像（由 photoshop 灰度并保存为 jpg）并尝试跳过这一步：

cvtColor(src,thr,CV_BGR2GRAY); //Convert to gray

当我再次运行 Visual Studio 中的相同代码时，我收到运行时间错误显示：

Unhandled exception at 0x00007FFE56A79E08 in image_capture.exe: Microsoft C++ exception: cv::Exception at memory location 0x000000C1D58FE1F0. occurred

在 countours.cpp 文件：

scanner = cvStartFindContours( img, storage, cntHeaderSize, mode, method, offset );

我想尽量避免使用 cvtColor，因为在我的应用程序中，我的输入图像是灰度图片。我的代码如下：

#include "stdafx.h"
#include <iostream>
#include "opencv2\highgui\highgui.hpp"
#include "opencv\cv.h"
#include "opencv2\imgproc\imgproc.hpp"

using namespace cv;
using namespace std;
int main()
{
 int largest_area=0;
 int largest_contour_index=0;
 Rect bounding_rect;

 Mat src = imread("src.jpg"); //Load source image
 Mat thr(src.rows,src.cols,CV_8UC1); 
 Mat dst(src.rows,src.cols,CV_8UC1,Scalar::all(0));
 //cvtColor(src,thr,CV_BGR2GRAY); //Convert to gray
 threshold(src, src,25, 255,THRESH_BINARY); //Threshold the gray

    vector<vector<Point>> contours; // Vector for storing contour
    vector<Vec4i> hierarchy;

    findContours( src, contours, hierarchy,CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE ); // Find the contours in the image

     for( int i = 0; i< contours.size(); i++ ) // iterate through each contour. 
      {
       double a=contourArea( contours[i],false);  //  Find the area of contour
       if(a>largest_area){
       largest_area=a;
       largest_contour_index=i;                //Store the index of largest contour
       bounding_rect=boundingRect(contours[i]); // Find the bounding rectangle for biggest contour
       }

      }

 Scalar color( 255,255,255);
 drawContours( dst, contours,largest_contour_index, color, CV_FILLED, 8, hierarchy ); // Draw the largest contour using previously stored index.
 rectangle(src, bounding_rect,  Scalar(0,255,0),1, 8,0);  
 imshow( "src", src );
 imshow( "largest Contour", dst );
 waitKey(0);
}

知道如何避免 cvtColor() 吗？

谢谢

Answer 1

根据 opencv documentation，findContour 函数的输入图像必须是 8 位单通道，因此您必须通过 threshold、[=12] 将输入图像更改为该类型=]，等等。如果您的图像是灰度图像，只需以 CV_LOAD_IMAGE_GRAYSCALE 模式加载它。

cv::Mat rawImg = imread(imgName, CV_LOAD_IMAGE_GRAYSCALE);

为什么openCV中的输入图像findContours()要转灰度？

Why is the input image findContours() in openCV has to be converted to grayscale?

c++

opencv

opencv3.0