Windows Phone实用开发技巧（32）：照片角度处理

 在实际项目中，可能须要用户从相册中选择图片而后进行相应的处理。可是不知道你们有没有发现这样一种状况，就是手机里看是竖着的，可是上传到微博或者哪里的时候确实横着的。一种状况是你拿手机竖着拍照得话，照片就是横着的，虽然在手机里看是竖着的。（可能有点抽象，遇到此状况的同窗应该深有感触）

那么咱们在客户端中应该如何处理这种状况呢？一种想法是获取图片的角度，若是是90°，就把照片翻转过来，再进行相应的操做。那这样就涉及到2个问题

1. 如何获取相册中照片的角度

2. 如何翻转已有的照片（流、或者Bitmap或者WriteableBitmap）

查看了系统的API，并无对相片的角度提供支持，可是咱们能够使用ExifLib开源库去作。

下述的方法就是获取选取图片的角度的

/// <summary> /// get angle of photo /// </summary> /// <param name="stream">photo stream</param> /// <param name="filename">photo name</param> /// <returns>angle of the photo</returns> public static int GetAngle(Stream stream, string filename)
{
    ExifLib.ExifOrientation _orientation;
    int _angle = 0;
    stream.Position = 0;
    JpegInfo info = ExifReader.ReadJpeg(stream, filename);
    if (info!=null)
    {
        _orientation = info.Orientation;
        switch (info.Orientation)
        {
            case ExifOrientation.TopLeft:
            case ExifOrientation.Undefined:
                _angle = 0;
                break;
            case ExifOrientation.TopRight:
                _angle = 90;
                break;
            case ExifOrientation.BottomRight:
                _angle = 180;
                break;
            case ExifOrientation.BottomLeft:
                _angle = 270;
                break;

        }
    }
    return _angle;
}

获取到角度后，若是角度是90°，便是反的，咱们须要将其纠正过来，能够使用以下的方法：

private Stream RotateStream(Stream stream, int angle)
{
    stream.Position = 0;
    if (angle % 90 != 0 || angle < 0) throw new ArgumentException();
    if (angle % 360 == 0) return stream;

    BitmapImage bitmap = new BitmapImage();
    bitmap.SetSource(stream);
    WriteableBitmap wbSource = new WriteableBitmap(bitmap);

    WriteableBitmap wbTarget = null;
    if (angle % 180 == 0)
    {
        wbTarget = new WriteableBitmap(wbSource.PixelWidth, wbSource.PixelHeight);
    }
    else     {
        wbTarget = new WriteableBitmap(wbSource.PixelHeight, wbSource.PixelWidth);
    }

    for (int x = 0; x < wbSource.PixelWidth; x++)
    {
        for (int y = 0; y < wbSource.PixelHeight; y++)
        {
            switch (angle % 360)
            {
                case 90:
                    wbTarget.Pixels[(wbSource.PixelHeight - y - 1) + x * wbTarget.PixelWidth] = wbSource.Pixels[x + y * wbSource.PixelWidth];
                    break;
                case 180:
                    wbTarget.Pixels[(wbSource.PixelWidth - x - 1) + (wbSource.PixelHeight - y - 1) * wbSource.PixelWidth] = wbSource.Pixels[x + y * wbSource.PixelWidth];
                    break;
                case 270:
                    wbTarget.Pixels[y + (wbSource.PixelWidth - x - 1) * wbTarget.PixelWidth] = wbSource.Pixels[x + y * wbSource.PixelWidth];
                    break;
            }
        }
    }
    MemoryStream targetStream = new MemoryStream();
    wbTarget.SaveJpeg(targetStream, wbTarget.PixelWidth, wbTarget.PixelHeight, 0, 100);
    return targetStream;
}

Demo源代码下载

原文Handling picture orientation in CameraCaptureTask in Windows Phone 7