Question

我已经实现了以下解决方案来压缩base 64映像并返回新的base 64字符串。它在Windows Phone 8.0中运行良好，但针对Windows Phone 8.1，似乎环境发生了变化。

WriteableBitmap没有BitmapImage的构造函数，WriteableBitmap没有函数SaveJpeg。我知道SaveJpeg是一个扩展，有没有办法将此扩展添加到Windows Phone 8.1？或者我可以使用任何API吗？我需要更改什么才能使8.1兼容？我在这里坚持下去了： - /

public static string Compress(String base64String, int compression)
{
    String compressedImage;

    byte[] imageBytes = Convert.FromBase64String(base64String);
    MemoryStream memoryStream = new MemoryStream(imageBytes, 0, imageBytes.Length);

    BitmapImage bitmapImage = new BitmapImage();
    bitmapImage.SetSource(memoryStream.AsRandomAccessStream());

    WriteableBitmap bmp = new WriteableBitmap(bitmapImage);

    int height = bmp.PixelHeight;
    int width = bmp.PixelWidth;
    int orientation = 0;
    int quality = 100 - compression;

    MemoryStream targetStream = new MemoryStream();
    bmp.SaveJpeg(targetStream, width, height, orientation, quality);

    byte[] targetImage = targetStream.ToArray();
    compressedImage = System.Convert.ToBase64String(targetImage);

    return compressedImage;
}

Answer 1

在WP8.1运行时我使用BitmapPropertySet来定义压缩级别。以下是在 Streams 上运行的示例代码：

/// <summary>
/// Method compressing image stored in stream
/// </summary>
/// <param name="sourceStream">stream with the image</param>
/// <param name="quality">new quality of the image 0.0 - 1.0</param>
/// <returns></returns>
private async Task<IRandomAccessStream> CompressImageAsync(IRandomAccessStream sourceStream, double newQuality)
{
    // create bitmap decoder from source stream
    BitmapDecoder bmpDecoder = await BitmapDecoder.CreateAsync(sourceStream);

    // bitmap transform if you need any
    BitmapTransform bmpTransform = new BitmapTransform() { ScaledHeight = newHeight, ScaledWidth = newWidth, InterpolationMode = BitmapInterpolationMode.Cubic };

    PixelDataProvider pixelData = await bmpDecoder.GetPixelDataAsync(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, bmpTransform, ExifOrientationMode.RespectExifOrientation, ColorManagementMode.DoNotColorManage);
    InMemoryRandomAccessStream destStream = new InMemoryRandomAccessStream(); // destination stream

    // define new quality for the image
    var propertySet = new BitmapPropertySet();
    var quality = new BitmapTypedValue(newQuality, PropertyType.Single);
    propertySet.Add("ImageQuality", quality);

    // create encoder with desired quality
    BitmapEncoder bmpEncoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, destFileStream, propertySet);
    bmpEncoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, newHeight, newWidth, 300, 300, pixelData.DetachPixelData());
    await bmpEncoder.FlushAsync();
    return destStream;
}

在Windows Phone 8.1上压缩并保存base64映像

1 个答案: