windowsphone7下图片格式的转换

windowsphone7和siverlight中的BitmapImage和Image提供的接口还是很比较大的区别的，总体来说siverlight的封装性更加健全一些。

同时在压缩bitmap的时候，siverlight会提供设置和访问图像dpi(dots per inch)和pixel的函数，但是wp7中只能访问和操作pixel。这样的话在wp7下，对于压缩一张图片来说，你可以很方便增加或减少像素，但是却很难访问它的dpi，那么图片的实际宽度和高度就很难定制了。

下面是对图片和文件流格式的一个转换类，可以参考一下：

    public class ImageUtil    {        /// <summary>        /// 将Image转换成二进制流        /// </summary>        /// <param name="sourceImage"></param>        /// <returns></returns>        public static byte[] ImageToByteArray(Image sourceImage)        {            return ImageSourceToByteArray(sourceImage.Source);        }        /// <summary>        /// 将ImageSource转换成二进制流        /// </summary>        /// <param name="sourceImage"></param>        /// <returns></returns>        public static byte[] ImageSourceToByteArray(ImageSource source)        {            BitmapSource bs = (BitmapSource)source;            using (MemoryStream ms = new MemoryStream())            {                WriteableBitmap writeableBitmap = new WriteableBitmap(bs);                Extensions.SaveJpeg(writeableBitmap, ms, bs.PixelWidth, bs.PixelHeight, 0, 100);                return ms.GetBuffer();            }        }        /// <summary>        /// 将二进制流转换为Image格式图片        /// </summary>        /// <param name="bitData"></param>        /// <returns></returns>        public static Image ByteArrayToImage(byte[] bitData)        {             Image image = new Image();            image.Source = ByteArrayToBitmapImage(bitData);            return image;        }        /// <summary>        /// 将二进制流转换为BitmapImage格式图片        /// </summary>        /// <param name="bitData"></param>        /// <returns></returns>        public static BitmapImage ByteArrayToBitmapImage(byte[] bitData)        {            BitmapImage bitmap = new BitmapImage();            using (MemoryStream ms = new MemoryStream(bitData))            {                bitmap.CreateOptions = BitmapCreateOptions.DelayCreation;                bitmap.SetSource(ms);                return bitmap;            }        }        /// <summary>        /// 将流数据写入jpeg文件        /// </summary>        /// <param name="stream"></param>        /// <param name="fileDirectory"></param>        /// <param name="filename"></param>        /// <param name="targetWidth"></param>        /// <param name="targetHeight"></param>        public static void WriteStreamObjectToJPEG(Stream stream, string fileDirectory,string filename, int targetWidth, int targetHeight)        {            using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())            {                if (!store.DirectoryExists(fileDirectory))                {                    store.CreateDirectory(fileDirectory);                }                WriteableBitmap bmpImage = new WriteableBitmap(targetWidth, targetHeight);                bmpImage.SetSource(stream);                using (IsolatedStorageFileStream isoStream =                    store.OpenFile(fileDirectory + '/' + filename, FileMode.OpenOrCreate))                {                    System.Windows.Media.Imaging.Extensions.SaveJpeg(bmpImage, isoStream, targetWidth, targetHeight, 0, 100);                }            }        }        /// <summary>        /// 将jpeg文件写入到数据流中        /// </summary>        /// <param name="filePath"></param>        /// <returns></returns>        public static BitmapImage ReadBitmapImageFromJPEG(string filePath)        {                               BitmapImage image = new BitmapImage();            Stream source = ReadStreamFromJPEG(filePath);            image.SetSource(source);            return image;        }        public static Stream ReadStreamFromJPEG(string filePath)        {            using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())            {                using (IsolatedStorageFileStream isoStream =                    store.OpenFile(filePath, FileMode.Open))                {                    Stream fileStream = new MemoryStream();                    isoStream.CopyTo(fileStream);                    isoStream.Close();                    isoStream.Dispose();                    store.Dispose();                    return fileStream;                }            }        }    }