这是我对流行的 C++ 示例代码答案的 Java 转换。我无法知道这段 Java 代码、原始 C++ 代码或底层方程式的真实性，也无法知道关于调整方程式的几条评论意味着什么，只能说它似乎有效。这是为了与高中生一起玩图像处理的实验目的。
package app;
import java.util.Arrays;
import java.util.stream.Collectors;
import org.opencv.highgui.HighGui;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Size;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.core.Point;
import org.opencv.core.Mat;
import org.opencv.core.MatOfPoint2f;
import org.opencv.imgproc.Imgproc;
import org.opencv.videoio.VideoCapture;
public class App {
static {
System.loadLibrary(Core.NATIVE_LIBRARY_NAME); // Load the native library.
}
static void warpMatrix(Size sz,
double theta,
double phi,
double gamma,
double scale,
double fovy,
Mat M,
MatOfPoint2f corners) {
double st=Math.sin(Math.toRadians(theta));
double ct=Math.cos(Math.toRadians(theta));
double sp=Math.sin(Math.toRadians(phi));
double cp=Math.cos(Math.toRadians(phi));
double sg=Math.sin(Math.toRadians(gamma));
double cg=Math.cos(Math.toRadians(gamma));
double halfFovy=fovy*0.5;
double d=Math.hypot(sz.width,sz.height);
double sideLength=scale*d/Math.cos(Math.toRadians(halfFovy));
double h=d/(2.0*Math.sin(Math.toRadians(halfFovy)));
double n=h-(d/2.0);
double f=h+(d/2.0);
Mat F=new Mat(4,4, CvType.CV_64FC1);//Allocate 4x4 transformation matrix F
Mat Rtheta=Mat.eye(4,4, CvType.CV_64FC1);//Allocate 4x4 rotation matrix around Z-axis by theta degrees
Mat Rphi=Mat.eye(4,4, CvType.CV_64FC1);//Allocate 4x4 rotation matrix around X-axis by phi degrees
Mat Rgamma=Mat.eye(4,4, CvType.CV_64FC1);//Allocate 4x4 rotation matrix around Y-axis by gamma degrees
Mat T=Mat.eye(4,4, CvType.CV_64FC1);//Allocate 4x4 translation matrix along Z-axis by -h units
Mat P=Mat.zeros(4,4, CvType.CV_64FC1);//Allocate 4x4 projection matrix
// zeros instead of eye as in github manisoftwartist/perspectiveproj
//Rtheta Z
Rtheta.put(0,0, ct);
Rtheta.put(1,1, ct);
Rtheta.put(0,1, -st);
Rtheta.put(1,0, st);
//Rphi X
Rphi.put(1,1, cp);
Rphi.put(2,2, cp);
Rphi.put(1,2, -sp);
Rphi.put(2,1, sp);
//Rgamma Y
Rgamma.put(0,0, cg);
Rgamma.put(2,2, cg);
Rgamma.put(0,2, -sg); // sign reversed? Math different convention than computer graphics according to Wikipedia
Rgamma.put(2,0, sg);
//T
T.put(2,3, -h);
//P Perspective Matrix (see also in computer vision a camera matrix or (camera) projection matrix is a 3x4 matrix which describes the mapping of a pinhole camera from 3D points in the world to 2D points in an image.)
P.put(0,0, 1.0/Math.tan(Math.toRadians(halfFovy)));
P.put(1,1, 1.0/Math.tan(Math.toRadians(halfFovy)));
P.put(2,2, -(f+n)/(f-n));
P.put(2,3, -(2.0*f*n)/(f-n));
P.put(3,2, -1.0);
System.out.println("P " + P.dump());
System.out.println("T " + T.dump());
System.out.println("Rphi " + Rphi.dump());
System.out.println("Rtheta " + Rtheta.dump());
System.out.println("Rgamma " + Rgamma.dump());
//Compose transformations
//F=P*T*Rphi*Rtheta*Rgamma;//Matrix-multiply to produce master matrix
//gemm(Mat src1, Mat src2, double alpha, Mat src3, double beta, Mat dst)
//dst = alpha*src1.t()*src2 + beta*src3.t(); // w or w/o the .t() transpose
// D=α∗AB+β∗C
Mat F1 = new Mat();
Mat F2 = new Mat();
Mat F3 = new Mat();
Core.gemm(P, T, 1, new Mat(), 0, F1);
Core.gemm(F1, Rphi, 1, new Mat(), 0, F2);
Core.gemm(F2, Rtheta, 1, new Mat(), 0, F3);
Core.gemm(F3, Rgamma, 1, new Mat(), 0, F);
P.release();
T.release();
Rphi.release();
Rtheta.release();
Rgamma.release();
F1.release();
F2.release();
F3.release();
//Transform 4x4 points
double[] ptsIn = new double[4*3];
double[] ptsOut = new double[4*3];
double halfW=sz.width/2, halfH=sz.height/2;
ptsIn[0]=-halfW;ptsIn[ 1]= halfH;
ptsIn[3]= halfW;ptsIn[ 4]= halfH;
ptsIn[6]= halfW;ptsIn[ 7]=-halfH;
ptsIn[9]=-halfW;ptsIn[10]=-halfH;
ptsIn[2]=ptsIn[5]=ptsIn[8]=ptsIn[11]=0;//Set Z component to zero for all 4 components
Mat ptsInMat = new Mat(1,4,CvType.CV_64FC3);
ptsInMat.put(0,0, ptsIn);
Mat ptsOutMat = new Mat(1,4,CvType.CV_64FC3);
System.out.println("ptsInMat " + ptsInMat + " " + ptsInMat.dump());
System.out.println("F " + F + " " + F.dump());
Core.perspectiveTransform(ptsInMat, ptsOutMat, F);//Transform points
System.out.println("ptsOutMat " + ptsOutMat + " " + ptsOutMat.dump());
ptsInMat.release();
F.release();
ptsOutMat.get(0, 0, ptsOut);
ptsOutMat.release();
System.out.println(toString(ptsOut));
System.out.println(halfW + " " + halfH);
//Get 3x3 transform and warp image
Point[] ptsInPt2f = new Point[4];
Point[] ptsOutPt2f = new Point[4];
for(int i=0;i<4;i++){
ptsInPt2f[i] = new Point(0, 0);
ptsOutPt2f[i] = new Point(0, 0);
System.out.println(i);
System.out.println("points " + ptsIn [i*3+0] + " " + ptsIn [i*3+1]);
Point ptIn = new Point(ptsIn [i*3+0], ptsIn [i*3+1]);
Point ptOut = new Point(ptsOut[i*3+0], ptsOut[i*3+1]);
ptsInPt2f[i].x = ptIn.x+halfW;
ptsInPt2f[i].y = ptIn.y+halfH;
ptsOutPt2f[i].x = (ptOut.x+1) * sideLength*0.5;
ptsOutPt2f[i].y = (ptOut.y+1) * sideLength*0.5;
System.out.println("ptsOutPt2f " + ptsOutPt2f[i]);
}
Mat ptsInPt2fTemp = Mat.zeros(4,1,CvType.CV_32FC2);
ptsInPt2fTemp.put(0, 0,
ptsInPt2f[0].x,ptsInPt2f[0].y,
ptsInPt2f[1].x,ptsInPt2f[1].y,
ptsInPt2f[2].x,ptsInPt2f[2].y,
ptsInPt2f[3].x,ptsInPt2f[3].y);
Mat ptsOutPt2fTemp = Mat.zeros(4,1,CvType.CV_32FC2);
ptsOutPt2fTemp.put(0, 0,
ptsOutPt2f[0].x,ptsOutPt2f[0].y,
ptsOutPt2f[1].x,ptsOutPt2f[1].y,
ptsOutPt2f[2].x,ptsOutPt2f[2].y,
ptsOutPt2f[3].x,ptsOutPt2f[3].y);
System.out.println("ptsInPt2fTemp " + ptsInPt2fTemp.dump());
System.out.println("ptsOutPt2fTemp " + ptsOutPt2fTemp.dump());
Mat warp=Imgproc.getPerspectiveTransform(ptsInPt2fTemp, ptsOutPt2fTemp);
warp.copyTo(M);
ptsInPt2fTemp.release();
warp.release();
//Load corners vector
if(corners != null)
{
corners.put(0,0, ptsOutPt2f[0].x, ptsOutPt2f[0].y//Push Top Left corner
, ptsOutPt2f[1].x, ptsOutPt2f[1].y//Push Top Right corner
, ptsOutPt2f[2].x, ptsOutPt2f[2].y//Push Bottom Right corner
, ptsOutPt2f[3].x, ptsOutPt2f[3].y);//Push Bottom Left corner
}
ptsOutPt2fTemp.release();
System.out.println("corners " + corners + " " + corners.dump());
}
static void warpImage(Mat src,
double theta,
double phi,
double gamma,
double scale,
double fovy,
Mat dst,
Mat M,
MatOfPoint2f corners){
double halfFovy=fovy*0.5;
double d=Math.hypot(src.cols(),src.rows());
double sideLength=scale*d/Math.cos(Math.toRadians(halfFovy));
System.out.println("d " + d + ", sideLength " + sideLength);
warpMatrix(src.size(), theta, phi, gamma, scale, fovy, M, corners);//Compute warp matrix
System.out.println("M " + M + " " + M.dump());
Imgproc.warpPerspective(src, dst, M, new Size(sideLength,sideLength));//Do actual image warp
}
public static void main(String[] args)
{
int c = 0;
Mat m = new Mat();
Mat disp = new Mat();
Mat warp = new Mat();
MatOfPoint2f corners = new MatOfPoint2f(new Point(0,0),new Point(0,0),new Point(0,0),new Point(0,0));
String filename = "lena.jpg";
m = Imgcodecs.imread(filename, Imgcodecs.IMREAD_COLOR);
if (m.empty()) {
System.out.println("Error opening image");
System.exit(-1);
}
double scale = 1.;
double fovy = 53.;
double halfFovy=fovy*0.5;
VideoCapture cap;
cap = new VideoCapture();
cap.open(0);
cap.read(m);
warpImage(m, 5, 50, 0, 1, 30, disp, warp, corners); // fovy = rad2deg(arctan2(640,480)) = 53 ??
while(true) {
cap.read(m);
double d=Math.hypot(m.cols(),m.rows());
double sideLength=scale*d/Math.cos(Math.toRadians(halfFovy));
Imgproc.warpPerspective(m, disp, warp, new Size(sideLength,sideLength));//Do actual image warp
HighGui.imshow("Disp", disp);
HighGui.imshow("Orig", m);
c = HighGui.waitKey(25);
if (c != -1) break;
}
m.release();
disp.release();
warp.release();
corners.release();
System.exit(0);
}
static String toString(double[] array) {
return Arrays.stream(array)
.mapToObj(i -> String.format("%5.2f", i))
.collect(Collectors.joining(", ", "[", "]"));
//.collect(Collectors.joining("|", "|", "|"));
}
}
