在IMAGE控件上打开了JPG图象后,用CANVAS作图的问题?(100分)

image1.Picture.LoadFromFile('111.jpg');
image1.Canvas.Ellipse(11,44,77,90);
运行会出现"can only modify an image if it contain a bitbmp"
我想以JPG图为背景,在其上用程序自绘一些图形.该如何做?
是否需要编程将image上的JPG图象转换成BMP?如果是该如何做?
在这先谢谢各位!!!

uses jpeg;
{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
Bip:TBitmap;
JpegImage: TJpegImage;
begin
Bip:=TBitmap.Create;
JpegImage:=TJpegImage.Create;
JpegImage.LoadFromFile('./wangzhen.jpg');
Bip.Assign(JPegImage);
Image1.Canvas.StretchDraw(image1.ClientRect,Bip);
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
image1.Canvas.Ellipse(11,44,77,90);
end;

TJpegImage单元是在那个单元定义的？

uses jpeg;
{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
JpegImage: TJpegImage;
begin
JpegImage:=TJpegImage.Create;
JpegImage.LoadFromFile('./wangzhen.jpg');
Image1.Canvas.StretchDraw(image1.ClientRect,JpegImage);
JpegImage.Free;
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
image1.Canvas.Ellipse(11,44,77,90);
end;

谢谢!我也已经查资料弄出来了,和你的思路基本一样.