having trouble with Discrete Cosine Transform program

anyone could point me out where did i do wrong? it seems that i can't
get back the original Lena image after the IDCT(inverse discrete cosine
transform) process. the output raw image is nothing more than a grey
colored canvas ...

//Header files declarations
#include <iostream.h>
#include <fstream.h>
#include <math.h>
#include <stdlib.h>

//Global declarations
const int pixel=256;
unsigned char impix[pixel][pixel];
double dctblock[pixel][pixel];
double idctblock[pixel][pixel];
static const double pi = 3.141593;

//Functions declarations
void copypixel();
void openfile();
void dct();
void idct();
void printdct();
void imageblock();
void printidct();
void printdctimage();
void printidctimage();
double c(int);

void main()
{
        openfile();
        imageblock();
        dct();
        printdct();
        printdctimage();
        idct();
        printidct();
        printidctimage();

}

void openfile()
{

        ifstream rawimage("lena.raw", ios::in|ios::binary);
        if(!rawimage)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        rawimage>>impix[i][j];
                }
        }

}

void imageblock()
{

        ofstream rawimagetxt("rawimage.txt", ios::out|ios::binary);
        if(!rawimagetxt)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        rawimagetxt<<int(impix[i][j])<<" ";
                }
        }

}

void dct()
{
        for(int u=0;u<pixel;u++) {
                for(int v=0;v<pixel;v++) {
                        double temp = 0.0;

                        for(int x=0;x<8;x++) {
                                for(int y=0;y<8;y++) {
                                        temp += impix[x][y] * cos(pi *
(2 * x + 1) * u / 16) *
cos(pi * (2 * y + 1) * v / 16);
                                }
                        }

                        dctblock[u][v] = temp * (c(u) / 2) * (c(v) /
2);
                }
        }

}

void printdct()
{

        ofstream dct("dct.txt", ios::out|ios::binary);
        if(!dct)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        dct<<dctblock[i][j]<<" ";
                }
        }

}

void printidct()
{

        ofstream idct("idct.txt", ios::out|ios::binary);
        if(!idct)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        idct<<idctblock[i][j]<<" ";
                }
        }

}

void printdctimage()
{

        ofstream dctimage("dct.raw", ios::out|ios::binary);
        if(!dctimage)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        dctimage<<dctblock[i][j];
                }
        }

}

void idct()
{
        for(int x=0;x<pixel;x++) {
                        for(int y=0;y<pixel;y++) {
                        double temp = 0.0;

                        for(int u=0;u<8;u++) {
                                for(int v=0;v<8;v++) {
                                        temp += (c(u) / 2) * (c(v) / 2)
* dctblock[u][v] * cos(pi * (2 *
x + 1) * u / 16) * cos(pi * (2 * y + 1) * v / 16);
                                }
                        }

                        idctblock[x][y] = temp;
                }
        }

}

void printidctimage()
{

        ofstream idctimage("idct.raw", ios::out|ios::binary);
        if(!idctimage)
        {
                cerr<<"Error in reading file\n";
                exit(1);
        }

        for(int i=0; i<pixel; i++)
        {
                for(int j=0; j<pixel; j++)
                {
                        idctimage<<idctblock[i][j];
                }
        }
}

double c(int number)
{
        if(number == 0)
        {
                return 1/sqrt(2);
        }
        else
        {
                return 1;
        } 
}