WP8.1开发对图片进行裁剪（截取）一部分

 1 #region
 2        /// <summary>
 3         /// 创建BitmapDecoder的像素转换器，并给转换设置属性（裁剪边框，缩放尺寸）
 4         /// </summary>
 5         /// <param name="decoder">要修改的解码数据</param>
 6         /// <param name="startX">裁剪边框左上角X位置</param>
 7         /// <param name="startY">裁剪边框左上角Y位置</param>
 8         /// <param name="width">裁剪边框宽度</param>
 9         /// <param name="height">裁剪边框高度</param>
10         /// <param name="scaledWidth">缩放后的像素宽度</param>
11         /// <param name="scaledHeight">缩放后的像素高度</param>
12         /// <returns></returns>
13         public static async Task<byte[]> GetPixelData(BitmapDecoder decoder, uint startX, uint startY, uint width, uint height, uint scaledWidth, uint scaledHeight)
14         {
15 
16 
17             //获取裁剪的边框尺寸，指定左上角位置（startX,startY）及裁剪高度height和宽度width；
18             #region define裁剪边框尺寸；
19             BitmapBounds bound = new BitmapBounds();
20             bound.X = startX;
21             bound.Y = startY;
22             bound.Width = width;
23             bound.Height = height;
24             #endregion
25 
26             //创建位图的像素数据的转换器
27             #region define转换器各属性
28             BitmapTransform tran = new BitmapTransform();
29 
30             //将裁剪尺寸的属性bound,赋值到tran.Bounds中
31             tran.Bounds = bound;
32 
33             //define转换器中缩放尺寸，
34             tran.ScaledWidth = scaledWidth;
35             tran.ScaledHeight = scaledHeight;
36             #endregion
37 
38             //获得像素数据
39             var v = await decoder.GetPixelDataAsync(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight, tran, ExifOrientationMode.IgnoreExifOrientation, ColorManagementMode.ColorManageToSRgb);
40             //从像素数据中得到二进制像素数据
41             byte[] pixels = v.DetachPixelData();
42             return pixels;//返回
43         }
44 #endregion

 1        public async static Task<WriteableBitmap> Get_Image()
 2         {
 3             
 4 
 5             //获得“图片.bmp”图片文件
 6             StorageFile imageFile = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///PetsData/图片.bmp"));
 7             //创建随机访问流，读出图片数据，放入到stream中
 8             using (IRandomAccessStream stream = await imageFile.OpenAsync(FileAccessMode.Read))
 9             {
10                 //x,y代表图片左上角位置，width、height代表裁剪边框的大小
11                   uint   x = 0;
12                   uint   y = 0; 
13                   uint   width = 28; 
14                   uint   height = 37; 
15          
16 //用解码类对数据流进行访问解码
17                 BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
18  //对获得的解码后的像素数据流进行修改，按边框x, y, width, height尺寸修改；
19                 //由于不对源图片进行缩放处理，所以GetPixelData()方法后两位参数直接赋源图片的尺寸像素decoder.PixelWidth, decoder.PixelHeight；
20                 byte[] pixels = await GetPixelData(decoder, x, y, width, height, decoder.PixelWidth, decoder.PixelHeight);
21                 //创建可写入的BitmapSource wp;
22                 WriteableBitmap wb = new WriteableBitmap(28, 37);
23                 Stream pixStream = wb.PixelBuffer.AsStream();
24 //写入裁剪的像素数据大小；
25                 pixStream.Write(pixels, 0, pixels.Length);
26 //返回WriteableBitmap类型的BitmapSource
27                 return wb;
28             }
29 
30         }