我有以下代码，该代码使用简单的算法进行傅立叶变换，但无法正常工作。
public int ft(int x, int y, int br, int a, int height, int width, int[][] pixelTemp, double c){
int r;
int g;
int b;
double avg;
double newCitra = 0;
int temp;
for (int i=0; i<height; i++){
for (int j=0; j<width; j++){
temp = pixelTemp[i][j];
r = (temp>>16)&0xff;
g = (temp>>8)&0xff;
b = temp&0xff;
avg = (r+g+b)/3;
if (Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))>0){
if(-2*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))>0){
newCitra = ((newCitra + (((double)avg/(double)(height*width)))*(sqrt(Math.pow((Math.cos(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))),2)+Math.pow((double)Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width)))),2)))));
} else {
newCitra = ((newCitra + (((double)avg/(double)(height*width)))*(sqrt(Math.pow((Math.cos(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))),2)-Math.pow((double)Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width)))),2)))));
}
} else {
if(-2*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))>0){
newCitra = (newCitra + ((double)avg/(double)(height*width))*((Math.cos(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width)))))+(double)Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))));
} else {
newCitra = (newCitra + ((double)avg/(double)(height*width))*((Math.cos(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width)))))-(double)Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))));
}
}
/*System.out.println(newCitra);*/
}
}
newCitra = (int) (Math.log(1+newCitra)*c);
int j = 30;
int i = 10;
/*System.out.println(Math.abs(sqrt(Math.pow((Math.cos(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width))))),2)-Math.pow((double)Math.sin(Math.toRadians(360*(((double)(i*x)/(double)height)+((double)(j*y)/(double)width)))),2))));*/
int p = (255<<24) | ((int)newCitra<<16) | ((int)newCitra<<8) | (int)newCitra;
return p;
}
结果如下：
显然我在这里犯了一些错误，但是我无法弄清楚，sqrt根中的值可以为负，这将导致NaN，但是我遵循的是傅立叶变换公式。
最佳答案
显然，您误解了这些公式。从另一个实现我有
real += tempreal[row][t] * cos[col][t] - tempimag[row][t] * sin[col][t];
imag += tempreal[row][t] * sin [col][t] + tempimag[row][t] * cos[col][t];
所以一旦有了实部和虚部，就求平方根
mag=Math.sqrt(real*real+imag*imag);
也在余弦/正弦中
cos[i][t]=Math.cos(2*Math.PI*t*i/n);
sin[i][t]=Math.sin(2*Math.PI*t*i/n);
我看不到正方形，而是成倍增加。
-
我已更新您的功能，如下所示：
a）实部和虚部需要分别计算，复数没有计算
b）一些重新安排
看来可行，如果尝试使用此处显示的图像http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm对角线条纹，您将获得该页面上所示的对角线。
public double ft(int x, int y, int br, int a, int height, int width, int[][] pixelTemp, double c){
int r;
int g;
int b;
double avg;
double newCitrar = 0, newCitrai = 0;
int temp;
double f=(double)1/(double)(height*width);
for (int i=0; i<width; i++){
for (int j=0; j<height; j++){
temp = pixelTemp[i][j];
// r = (temp>>16)&0xff;
// g = (temp>>8)&0xff;
// b = temp&0xff;
avg = temp; // (r+g+b)/3;
newCitrar = newCitrar + avg*Math.cos(2*Math.PI*(((double)(i*x)/(double)width)+((double)(j*y)/(double)height)));
newCitrai=newCitrai+avg*Math.sin(2*Math.PI*(((double)(i*x)/(double)width)+((double)(j*y)/(double)height)));
}
}
newCitrar *=f;
newCitrai *=f;
double newCitra=Math.sqrt(newCitrar*newCitrar+newCitrai*newCitrai);
return newCitra;
}
在显示方面，我有以下内容：
BufferedImage bim=null;
try {
bim=ImageIO.read(new File("str.gif"));
}
catch (Exception ex) { System.err.println("error"); }
int wc=bim.getWidth(), hc=bim.getHeight();
BufferedImage b2=new BufferedImage(wc, hc, BufferedImage.TYPE_INT_RGB);
int[] pix=bim.getRGB(0, 0, wc, hc, null, 0, wc);
int[][] pix2=new int[wc][hc];
double ri;
for(i=0; i<wc; i++)
for(j=0; j<hc; j++) {
int rr=(pix[i+j*wc]&0x00ff0000)>>16, rg=(pix[i+j*wc]&0x0000ff00)>>8, rb=pix[i+j*wc]&0x000000ff;
ri=0.2126*rr+0.7152*rg+0.0722*rb;
pix2[i][j]=(int)ri;
}
double max=0;
for(i=0; i<wc; i++)
for(j=0; j<hc; j++) {
if(i%10==0 && j%10==0) System.out.println(i+" "+j);
double ki=ft(i, j, 0, 0, hc, wc, pix2, 1);
if(ki>max) max=ki;
b2.setRGB(i, j, (int)ki);
}
saveImageIO(b2, (time/1000)+"f-1");
double cc=255./Math.log(1+max);
System.out.println(max+" "+cc);
for(i=0; i<wc; i++)
for(j=0; j<hc; j++) {
b2.setRGB(i, j, (int) (Math.log(1+(b2.getRGB(i, j)&0x00ffffff))*cc));
}
saveImageIO(b2, (time/1000)+"f-2");
关于java - 傅里叶变换在Java中获取幅度值，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/41129980/