离散余弦变换 实现了一维DCT、二维DCT及其反变换
void initDCTParam(int deg)
{
// deg 为DCT变换数据长度的幂
if(bHasInit)
{
return; //不用再计算查找表
}
int total, halftotal, i, group, endstart, factor;
total = 1 << deg;
if(C != NULL) delete []C;
C = (double *)new double[total];
halftotal = total >> 1;
for(i=0; i < halftotal; i++)
C[total-i-1]=(double)(2*i+1);
for(group=0; group < deg-1; group++)
{
endstart=1 << (deg-1-group);
int len = endstart >> 1;
factor=1 << (group+1);
for(int j = 0;j < len; j++)
C[endstart-j-1] = factor*C[total-j-1];
}
for(i=1; i < total; i++)
C[i] = 2.0*cos(C[i]*PI/(total << 1)); ///C[0]空着，没使用
bHasInit=true;
}
DCT变换过程可分为两部分：前向追底和后向回根
前向追底：
void dct_forward(double *f,int deg)
{
// f中存储DCT数据
int i_deg, i_halfwing, total, wing, wings, winglen, halfwing;
double temp1,temp2;
total = 1 << deg;
for(i_deg = 0; i_deg < deg; i_deg++)
{
wings = 1 << i_deg;
winglen = total >> i_deg;
halfwing = winglen >> 1;
for(wing = 0; wing < wings; wing++)
{
for(i_halfwing = 0; i_halfwing < halfwing; i_halfwing++)
{
temp1 = f[wing*winglen+i_halfwing];
temp2 = f[(wing+1)*winglen-1-i_halfwing];
if(wing%2)
swap(temp1,temp2); // 交换temp1与temp2的值
f[wing*winglen+i_halfwing] = temp1+temp2;
f[(wing+1)*winglen-1-i_halfwing] =
(temp1-temp2)*C[winglen-1-i_halfwing];
}
}
}
}
后向回根： void dct_backward(double *f,int deg)
{
// f中存储DCT数据
int total,i_deg,wing,wings,halfwing,winglen,i_halfwing,temp1,temp2;
total = 1 << deg;
for(i_deg = deg-1; i_deg >= 0; i_deg--)
{
wings = 1 << i_deg;
winglen = 1 << (deg-i_deg);
halfwing = winglen >> 1;
for(wing = 0; wing < wings; wing++)
{
for(i_halfwing = 0; i_halfwing < halfwing; i_halfwing++)
{
//f[i_halfwing+wing*winglen] = f[i_halfwing+wing*winglen];
if(i_halfwing == 0)
{
f[halfwing+wing*winglen+i_halfwing] =
0.5*f[halfwing+wing*winglen+i_halfwing];
}
else
{
