uses GdiPlus;
procedure TForm1.Button1Click(Sender: TObject);
var
img: IGPImage;
bit: IGPBitmap;
g: IGPGraphics;
begin
img := TGPImage.Create('c:\temp\01.png');
bit := TGPBitmap.Create(img.Width, img.Height, PixelFormat1bppIndexed);
g := TGPGraphics.Create(bit);
g.DrawImage(img, 0, 0, img.Width, img.Height);
bit.Save('c:\temp\02.png', TGPImageFormat.Png);
end;