Visual C++ :: Slow Performances Using Bitmap / GDI

I am trying to do this:

while(1)
{
CaptureScreenshot (as BMP)
Convert screenshot to 24 bit instead of 32 bit
Resize screenshot size
Get the BMP bits array of the resized screenshot
}

I have it working but the best i could get is 18 iteration (screenshots) per second. This is what i do:

Code:
Start() {
ULONG_PTR gdiplusToken=0;
HDC mhCompatibleDC;
HBITMAP mhCompatibleBitmap;
HWND mhDesktopWnd;
HDC mhDesktopDC;
byte*piRGB=new byte[1200*900*3]

[Code] .....

Here i do things with piRGB but these things are not counted it the timer so you can assume here the code ends . As said as the code looks now, i can fill piRGB ~18 times (18loops) in 1 second. I must improve that...