关于 图像的局部放大的问题？

private void menuItem24_Click(object sender, System.EventArgs e)
{
canvas.Width *=2;
canvas.Height *=2;
Rectangle rect = canvas.DisplayRectangle;
Graphics gc = canvas.CreateGraphics();
gc.InterpolationMode = InterpolationMode.HighQualityBicubic;
//gc.CompositingQuality = CompositingQuality.HighQuality;
gc.DrawImage(canvas.Image,rect);
canvasmanager.Scale *=2;
canvasmanager.currentTool.Scale = canvasmanager.Scale;
canvasmanager.currentTool.Rect = rect;
canvasmanager.currentTool.graphic = canvas.CreateGraphics();
//canvasmanager.ReChooseTool(); }