c++ - GetPixel is WAY too slow -

i have bunch of squares , each has specific identity/symbol need identify. far have like:

#include <iostream> #include <windows.h>  using namespace std;  int main() {     hdc dc = getdc(0);     colorref color;     int sum, x, y;      while (true) {         sum = 0;         sleep(100);         (x = 512; x < 521; x++) {             (y = 550; y < 565; y++) {                 color = getpixel(dc, x, y);                 sum = getrvalue(color) + getbvalue(color) + getgvalue(color);             }         }         cout << "sum: " << sum << endl;     }      return 0; } 

obviously scans 1 block far. problem somehow though it's on 100 pixels, takes insanely long time. can't imagine going on. takes on second, maybe 2 seconds, each repetition. can do? there has faster way this. if can't query individual pixels, there way region of screen? zone not inside program's window.