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我寫了一個程序，加載，保存，並在黑白png圖像上執行fft和ifft。經過許多調試頭痛之後，我終於得到了一些連貫的輸出，只是發現它扭曲了原始圖像。怪異但密切fft和ifft的圖像在c + +
輸入：
FFT：
IFFT：
據我已經測試，像素i的數據每個數組都被正確存儲和轉換。像素存儲在兩個數組中，包含每個像素的b/w值的'data'和'data'的兩倍長的'complex_data'，並以交替索引存儲每個像素的實際b/w值和虛部。我的fft算法在像'complex_data'這樣的數組結構上運行。代碼讀取用戶的命令後，這裏是有問題的代碼：
if (cmd == "fft")
{
if (height > width) size = height;
else size = width;
N = (int)pow(2.0, ceil(log((double)size)/log(2.0)));
temp_data = (double*) malloc(sizeof(double) * width * 2); //array to hold each row of the image for processing in FFT()
for (i = 0; i < (int) height; i++)
{
for (j = 0; j < (int) width; j++)
{
temp_data[j*2] = complex_data[(i*width*2)+(j*2)];
temp_data[j*2+1] = complex_data[(i*width*2)+(j*2)+1];
}
FFT(temp_data, N, 1);
for (j = 0; j < (int) width; j++)
{
complex_data[(i*width*2)+(j*2)] = temp_data[j*2];
complex_data[(i*width*2)+(j*2)+1] = temp_data[j*2+1];
}
}
transpose(complex_data, width, height); //tested
free(temp_data);
temp_data = (double*) malloc(sizeof(double) * height * 2);
for (i = 0; i < (int) width; i++)
{
for (j = 0; j < (int) height; j++)
{
temp_data[j*2] = complex_data[(i*height*2)+(j*2)];
temp_data[j*2+1] = complex_data[(i*height*2)+(j*2)+1];
}
FFT(temp_data, N, 1);
for (j = 0; j < (int) height; j++)
{
complex_data[(i*height*2)+(j*2)] = temp_data[j*2];
complex_data[(i*height*2)+(j*2)+1] = temp_data[j*2+1];
}
}
transpose(complex_data, height, width);
free(temp_data);
free(data);
data = complex_to_real(complex_data, image.size()/4); //tested
image = bw_data_to_vector(data, image.size()/4); //tested
cout << "*** fft success ***" << endl << endl;
void FFT(double* data, unsigned long nn, int f_or_b){ // f_or_b is 1 for fft, -1 for ifft
unsigned long n, mmax, m, j, istep, i;
double wtemp, w_real, wp_real, wp_imaginary, w_imaginary, theta;
double temp_real, temp_imaginary;
// reverse-binary reindexing to separate even and odd indices
// and to allow us to compute the FFT in place
n = nn<<1;
j = 1;
for (i = 1; i < n; i += 2) {
if (j > i) {
swap(data[j-1], data[i-1]);
swap(data[j], data[i]);
}
m = nn;
while (m >= 2 && j > m) {
j -= m;
m >>= 1;
}
j += m;
};
// here begins the Danielson-Lanczos section
mmax = 2;
while (n > mmax) {
istep = mmax<<1;
theta = f_or_b * (2 * M_PI/mmax);
wtemp = sin(0.5 * theta);
wp_real = -2.0 * wtemp * wtemp;
wp_imaginary = sin(theta);
w_real = 1.0;
w_imaginary = 0.0;
for (m = 1; m < mmax; m += 2) {
for (i = m; i <= n; i += istep) {
j = i + mmax;
temp_real = w_real * data[j-1] - w_imaginary * data[j];
temp_imaginary = w_real * data[j] + w_imaginary * data[j-1];
data[j-1] = data[i-1] - temp_real;
data[j] = data[i] - temp_imaginary;
data[i-1] += temp_real;
data[i] += temp_imaginary;
}
wtemp = w_real;
w_real += w_real * wp_real - w_imaginary * wp_imaginary;
w_imaginary += w_imaginary * wp_real + wtemp * wp_imaginary;
}
mmax=istep;
}}
我IFFT是一樣的只能用f_or_b設置爲-1，而不是1我的程序上的每一行調用FFT（），轉置該圖像再次調用每行的FFT（），然後轉換回來。我的索引可能有錯誤嗎？
與你的問題沒有關係，但你應該真的在C++中避免malloc/free，並使用new/delete代替。 – Christophe
編碼中的舊習慣c。 –
[Dangerous habit]（http://stackoverflow.com/questions/184537/in-what-cases-do-i-use-malloc-vs-new）只要你使用非POD數據 – Christophe