c++ - 通过opencv中的选定像素裁剪图像

Question

我试图通过将图像的高度和宽度减半并裁剪来将原始图像减半。 [待裁剪图片][1]

下面是我的代码，但它导致运行时异常，并且 .exe 文件停止工作并出现以下错误:

OpenCV Error: Assertion failed (rect.width >= 0 && rect.height >= 0 && rect.x < image->width && rect.y < image->height && rect.x + rect.width >= (int)(rect.width > 0) && rect.y + rect.height >= (int)(rect.height > 0)) in cvSetImageROI, file C:\Development\opencv\sources\modules\core\src\array.cpp, line 3006

This application has requested the Runtime to terminate it in an unusual way.

Please contact the application's support team for more information.

下面是代码:

#include <iostream>
#include <string>
#include <opencv/cv.h>
#include <opencv/cxcore.h>
#include <opencv/highgui.h>

using namespace std;
using namespace cv;

int main(int argc, char** argv) {
   IplImage *img1 = cvLoadImage("image/testcase.jpg");
   cvNamedWindow("Image1:",1);
   cvShowImage("Image1:",img1);
   cout << "Width:" <<  img1->width <<" pixels"<< endl;
   cout << "Height:" <<  img1->height <<" pixels"<< endl;
   int width = img1->width ;
   int lenght = img1->height;

   // cropping the image

   Rect roi;
   roi.x = width;
   roi.y = lenght;
   roi.width = (roi.x)/2;
   roi.height = (roi.y)/2;

   Mat image_test;
   image_test = imread("image/testcase");
   // Must have dimensions of output image

   IplImage* cropped = cvCreateImage(cvSize(roi.width,roi.height), img1->depth, img1->nChannels );

   cvSetImageROI(img1, roi);
   cvCopy(img1, cropped);
   cvResetImageROI(img1);
   cvNamedWindow( "Cropped Image", 1 );
   cvShowImage( "Cropped Image", cropped );
   cvSaveImage ("savedImage/cropped.jpg" , cropped);
   waitKey(0);
   return 0;
}

Answer 1

问题出在您的 roi 中。由于 x=width 和 y=length，您使用的是图像的 roi。 x 和 y 应该是您的投资返回率的左上角。在这种情况下，它们都应该是 0。

你不应该使用过时的 C api。

要裁剪图像的左上部分，您可以简单地:

#include<opencv2/opencv.hpp>
using namespace cv;

int main()
{
    // Load image
    Mat3b img = imread("path_to_image");

    // Define the roi
    Rect roi(0, 0, img.cols / 2, img.rows / 2);

    // Crop
    Mat3b crop = img(roi);

    // Show result
    imshow("Original", img);
    imshow("Crop", crop);
    waitKey();

    return 0;
}

制作: