DCT快速变换
2010-07-25 20:45:40 来源:WEB开发网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
{
temp1=bitrev(i_halfwing,deg-i_deg-1); // bitrev为位反序
temp2=bitrev(i_halfwing-1,deg-i_deg-1); // 第一参数为要变换的数
// 第二参数为二进制长度
f[halfwing+wing*winglen+temp1] =
f[halfwing+wing*winglen+temp1]-f[halfwing+wing*winglen+temp2];
}
}
}
}
}
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