我的裁剪逻辑有什么问题？

Question

我试图通过从中间裁剪来将肖像图像裁剪成特定的景观尺寸，而我似乎在做错事。现在，我有以下代码：

// Check the orientation 
if(original.Height > original.Width) { 
    var bmp = new Bitmap(original); 
    int cropHeightOffset = (desiredHeight - original.Height)/2; 
    var totalArea = new Rectangle(new Point(0, 0), 
            new Size(original.Width, original.Height)); 
    var cropArea = new Rectangle(new Point(0, cropHeightOffset), 
           new Size(desiredWidth, desiredHeight)); 

    // Create new blank image of the desired size 
    var newBmp = new Bitmap(bmp, new Size(desiredWidth, desiredHeight)); 

    // Crop image 
    var cropper = Graphics.FromImage(newBmp); 

    // Draw it 
    cropper.DrawImage(bmp, totalArea, cropArea, GraphicsUnit.Pixel); 

    // Save 
    original.Dispose(); 
    newBmp.Save(imagePath, ImageFormat.Jpeg); 
} 

发生这种情况时它本质上调整图像大小（从而扭曲它），而不是种植它。

如果我在cropper.DrawImage调用中切换totalArea和cropArea，则它会从底部开始裁剪，但它将图像循环两次（但仍是正确的大小）。

我完全困惑于如何正确地做到这一点。

---

编辑：以下是我尝试过的一些事例。有什么我没有得到，我只是不知道是什么。

使用奥利弗代码：

  var targetArea = new Rectangle(new Point(0, 0), new Size(desiredWidth, desiredHeight)); 
      var cropArea = new Rectangle(new Point(0, cropHeightOffset), new Size(desiredWidth, desiredHeight)); 

      ... 

      // Draw it 
      cropper.DrawImage(bmp, targetArea, cropArea, GraphicsUnit.Pixel); 

给我http://dl.dropbox.com/u/6753359/crop/7278482-2.jpeg

  var targetArea = new Rectangle(new Point(0, 0), new Size(desiredWidth, desiredHeight)); 
      var cropArea = new Rectangle(new Point(0, cropHeightOffset), new Size(original.Width, original.Height)); 
      ...... 

      // Draw it 
      cropper.DrawImage(bmp, cropArea, targetArea, GraphicsUnit.Pixel); 

给我http://dl.dropbox.com/u/6753359/crop/7278482-1.jpeg

原始图像是：http://dl.dropbox.com/u/6753359/crop/7278482%20orig.jpeg

Answer 1

您必须指定目标区域，不是总面积：

var newSize = new Size(desiredWidth, desiredHeight); 
var targetArea = new Rectangle(new Point(0, 0), newSize); 
var cropArea = new Rectangle(new Point(0, cropHeightOffset), newSize); 
... 
cropper.DrawImage(bmp, targetArea, cropArea, GraphicsUnit.Pixel);