如何将截屏后BMP的图片按比例缩小，下面是我的原代码： ( 积分: 100 )

procedure ScreenCap(LeftPos,TopPos,RightPos,BottomPos:integer);
begin
bmpstream := Tmemorystream.Create;
RectWidth:=RightPos-LeftPos;
RectHeight:=BottomPos-TopPos;
SourceDC:=CreateDC('DISPLAY','','',nil);
DestDC:=CreateCompatibleDC(SourceDC);
Bhandle:=CreateCompatibleBitmap(SourceDC,RectWidth,RectHeight);
SelectObject(DestDC,Bhandle);
BitBlt(DestDC,0,0,RectWidth,RectHeight,SourceDC,LeftPos,TopPos,SRCCOPY);
Bitmap:=TBitmap.Create;
Bitmap.Handle:=BHandle;
BitMap.SaveToStream(BmpStream);
BmpStream.Position:=0;
LeftSize:=BmpStream.Size;
Bitmap.Free;
DeleteDC(DestDC);
ReleaseDC(Bhandle,SourceDC);

end;

procedure TForm1.Button1Click(Sender: TObject);
begin
w:=screen.Width;
h:=screen.Height;
form1.AutoSize:=true;
screencap(0,0,w,h);
image1.AutoSize:=true;
image1.Picture.Bitmap.LoadFromStream(bmpstream);
bmpstream.Free;
end;

procedure ScreenCap(LeftPos,TopPos,RightPos,BottomPos:integer);
begin
bmpstream := Tmemorystream.Create;
RectWidth:=RightPos-LeftPos;
RectHeight:=BottomPos-TopPos;
SourceDC:=CreateDC('DISPLAY','','',nil);
DestDC:=CreateCompatibleDC(SourceDC);
Bhandle:=CreateCompatibleBitmap(SourceDC,RectWidth,RectHeight);
SelectObject(DestDC,Bhandle);
BitBlt(DestDC,0,0,RectWidth,RectHeight,SourceDC,LeftPos,TopPos,SRCCOPY);
Bitmap:=TBitmap.Create;
Bitmap.Handle:=BHandle;
BitMap.SaveToStream(BmpStream);
BmpStream.Position:=0;
LeftSize:=BmpStream.Size;
Bitmap.Free;
DeleteDC(DestDC);
ReleaseDC(Bhandle,SourceDC);

end;

procedure TForm1.Button1Click(Sender: TObject);
begin
w:=screen.Width;
h:=screen.Height;
form1.AutoSize:=true;
screencap(0,0,w,h);
image1.AutoSize:=true;
image1.Picture.Bitmap.LoadFromStream(bmpstream);
bmpstream.Free;
end;

ScreenCap是截屏函数没问题，当我读取图象想按比例缩小时无法实现：
// image1.AutoSize:=true;
// image1.Picture.Bitmap.LoadFromStream(bmpstream);
// bmpstream.Free;
上面代码该如何改？我原先想使用TJPEGIMAGE的COMPRESSQUALITY属性来实现，可是还是有问题，请教高人，这问题如何解决？

stretchdraw
给个例子 可以把image里的图片按比例缩小但是效果欠佳，不过是最简单的
procedure TForm1.Button1Click(Sender: TObject);
var
bt:tbitmap;
begin
bt:=tbitmap.create;
bt.width:=image2.Width;
bt.height:=image2.Height;
bt.canvas.StretchDraw(rect(0,0,image2.Width,image2.Height),image1.Picture.Graphic );
bt.savetofile('d:/1.bmp');
image2.Picture.Bitmap.Assign(bt);
bt.free;
end;

StretchDraw,StretchBlt是从源图象中移动图象到指定矩形
这个方法可行！还有其他更好方法吗？

image的Stretch设为True.

Stretch没用，不可以将图片按比例缩小

StretchBlt不仅仅限于image图片框，你可以自己做个timage，去存图片，既然你可以用流用个timage也没什么嘛

我一直这么用。。。
var
h:hwnd;
dc:hdc;
begin
try
bit.PixelFormat:=pf32bit;
bit.Width:=128;
bit.Height:=96;
h:=frm_window.Handle;
dc:=getdc(h);
stretchBlt(bit.Canvas.Handle,0,0,128,96,DC, frm_window.Width, frm_window.Height,frm_window.Width,frm_window.Height, SRCCOPY);
releasedc(h,dc);
except
end;
end;

谢谢funxu以及hs-kill