图像变换

利用OpenCV实现图像的仿射变换

仿射变换可以形象的表示成如下形式：一个平面内任意的平行四边形ABCD可以被仿射变换映射为另一个平行四边形A'B'C'D'，如果四边形的面积不等于0，仿射变换就被这两个平行四边形（其中的三个顶点）唯一的定义，这里注意确定一个平行四边形只需要三个顶点。我们可以把仿射变换想象成把一幅图像画到一个胶板上，在胶板的角上推或拉以得到不同的平行四边形。

下面的程序实现了对图像的仿射变换，还包括图像旋转、缩放这两个重要的子集。
#include <cv.h>
#include <highgui.h>
#include <stdio.h>
#include <iostream.h>

int main( int argc, char** argv )
{
	CvPoint2D32f srcTri[3],dstTri[3];
	CvMat* rot_mat = cvCreateMat( 2, 3, CV_32FC1 );
	CvMat* warp_mat = cvCreateMat( 2, 3, CV_32FC1 );
	IplImage *src, *dst, *srcBak, *dstBak;
	int TLx = 0, TLy = 0, TRx = 0, TRy = 0, DLx = 0, DLy = 0;
	double angle = 40, scale = 0.8;
	float delta = 0.01;
	int PressKey;
	char name[1][80];

    if(!(src=cvLoadImage("C:/Users/jinxing/Desktop/Tests/test/Debug/lena.bmp",1)) )
	{
		printf("Input Error\n");
		return -1;
	}

        srcTri[0].x = 0;// Top left
	srcTri[0].y = 0;
	srcTri[1].x = src->width-1;//Top right
	srcTri[1].y = 0;
	srcTri[2].x = 0;//Down left
	srcTri[2].y = src->height-1;

	dst = cvCloneImage(src);
	srcBak = cvCloneImage(src);
	cvCopy(src,srcBak);
	dst->origin = src->origin;
	cvZero(dst);
	cvNamedWindow( "AffineTransform", 1 );
	CvFont font = cvFont( 1, 1 );

	while(1)
	{
		dstTri[0].x = srcBak->width*delta*(TLx%101);
		dstTri[0].y = srcBak->height*delta*(TLy%101);
		dstTri[1].x = srcBak->width-1 - srcBak->width*delta*(TRx%101);
		dstTri[1].y = srcBak->height*delta*(TRy%101);
		dstTri[2].x = srcBak->width*delta*(DLx%101);
		dstTri[2].y = srcBak->height-1 - srcBak->height*delta*(DLy%101);
                cvGetAffineTransform(srcTri,dstTri,warp_mat);
		cvWarpAffine(srcBak,dst,warp_mat);
		cvCopy(dst,src);

                CvPoint2D32f center = cvPoint2D32f(src->width/2,src->height/2);
		cv2DRotationMatrix(center,angle,scale,rot_mat);
		cvWarpAffine(src,dst,rot_mat);
		dstBak = cvCloneImage(dst);
	        cvCopy(dst,dstBak);
		//--------------------------字符显示--------------------------------//
		char buf[8];
		char dspStr1[32] = {'|'};	
		char dspStr2[32] = {'|'};	
		char dspStr3[32] = {'|'};
		char dspStr4[32] = {'|'};

		memset(buf,'/0',sizeof(buf));
		strcat(dspStr1,itoa(TLx%101,buf,10));
		strcat(dspStr1,",");
		strcat(dspStr1,itoa(TLy%101,buf,10));
		strcat(dspStr1,"|TL");

		strcat(dspStr2,"angle=");
		strcat(dspStr2,itoa(int(angle),buf,10));
		strcat(dspStr2,",scale=");
		strcat(dspStr2,itoa(int(scale*100),buf,10));
		strcat(dspStr2,"%|");

		strcat(dspStr3,itoa(TRx%101,buf,10));
		strcat(dspStr3,",");
		strcat(dspStr3,itoa(TRy%101,buf,10));
		strcat(dspStr3,"|TR");

		strcat(dspStr4,itoa(DLx%101,buf,10));
		strcat(dspStr4,",");
		strcat(dspStr4,itoa(DLy%101,buf,10));
		strcat(dspStr4,"|DL");

		cvPutText(dst,dspStr1,cvPoint(dst->width-120,20),&font,cvScalar(0,0xff));
		cvPutText(dst,dspStr2,cvPoint(dst->width-180,80),&font,cvScalar(0,0xff));
		cvPutText(dst,dspStr3,cvPoint(dst->width-120,40),&font,cvScalar(0,0xff));
		cvPutText(dst,dspStr4,cvPoint(dst->width-120,60),&font,cvScalar(0,0xff));
		//---------------------------------------------------------------------//
		cvShowImage( "AffineTransform", dst );
		PressKey = cvWaitKey();
		printf("%c is pressed\n",PressKey);
		switch(PressKey)
		{
		case '1':
			TLx++;
			break;
		case 'q':
			TLx--;
			break;
		case '2':
			TLy++;
			break;
		case 'w':
			TLy--;
			break;
		case '3':
			TRx++;
			break;
		case 'e':
			TRx--;
			break;
		case '4':	
			TRy++;
			break;
		case 'r':
			TRy--;
			break;
		case '5':	
			DLx++;
			break;
		case 't':
			DLx--;
			break;
		case '6':
			DLy++;
			break;
		case 'y':
			DLy--;
			break;
		case '7':
			angle++;
			break;
		case 'u':
			angle--;
			break;
		case '8':
			scale+=0.01;
			break;
		case 'i':
			scale-=0.01;
			break;
		case 27:
			cvReleaseImage(&dst);
			cvDestroyWindow("AffineTransform");
			cvReleaseMat(&rot_mat);
			cvReleaseMat(&warp_mat);
			return 0;
		case 's':
			cout<<"Input the filename:"<<endl;
			cin>>name[0];
			cvSaveImage( name[0], dstBak );
			cout<<name[0]<<" is saved."<<endl;
			break;
		default:
			cout<<"Input Error."<<endl;
			cout<<"Input 1 2 3 4 5 6 7 8 q w e r t y to change the coordinate."<<endl<<
				"Input u and i to change the angle and scale."<<endl<<"Input s to save the image."<<endl
				<<"Input the esc to quit."<<endl;
			break;
		}
	}
	cvDestroyWindow("AffineTransform");
	cvReleaseImage(&dst);
	cvReleaseMat(&rot_mat);
	cvReleaseMat(&warp_mat);
	return 0;
}
程序的执行结果：

程序执行后，可自己调节三个顶点的坐标，以获得不同的对应关系，即可得到不同的仿射变换矩阵（大小为2×3）。还可调节旋转角度以及缩放尺度。