How do I obtain the RGB values of each pixel from the top left corner to the bottom right corner of the current top image on the screen?

How do I obtain the RGB values of each pixel from the top left corner to the bottom right corner of the current top image on the screen? Delphi/Windows SDK/API
Http://www.delphi2007.net/DelphiMultimedia/html/delphi_20061005161844269.html
How do I obtain the RGB values of each pixel from the top left corner to the bottom right corner of the current top image on the screen?
It is the pixel on the screen, not the pixel on the form.

Procedure tform1.button1click (Sender: tobject );
VaR
DC: HDC;
B: tbitmap;
Begin
DC: = getdc (hwnd_desktop );
Try
B: = image1.picture. Bitmap;
B. Width: = screen. width;
B. Height: = screen. height;
Bitblt (B. Canvas. Handle, 0, 0, screen. Width, screen. height,
DC, 0, 0, srccopy );
Finally
Releasedc (hwnd_desktop, DC );
End;
End;

I don't need to talk about how to retrieve pixels from tbitmap.

positive solution: