应用显示图形：算法优化

Question

for(int i =0; i {
nStartPos = i*700;
for(int j = 0; j {
nPos=nStartPos+j;
pRgbTable = (LPRGBQUAD)(lpBitmapBits + nPos * 3);
pRgbTable->rgbBlue = GetBValue(Echo_Color[box1[699-j][499-i]]);
pRgbTable->rgbGreen = GetGValue(Echo_Color[box1[699-j][499-i]]);
pRgbTable->rgbRed = GetRValue(Echo_Color[box1[699-j][499-i]]);
pRgbTable->rgbReserved = 0;

}

}   

给500*700的bmp赋值，现在开销100ms，算法应该怎么优化，Echo_color[box1[699-j][499-i]]是COLORREF。