UWP：您如何降低所选图像的质量？

Question

我的代码允许用户使用文件选择器选择图像并将图像转换为字节数组以便可以序列化。在查看图像集合时，如果我有太多，应用程序会崩溃并且无法加载。当我使用视觉工作室进行调试时，它运行良好，但加载图像需要很长时间。我相信它会超时，因为加载需要很长时间。获取存储文件后。如何降低 BitmapImage 的质量，以便在序列化时不会花费很长时间来加载？

 private async void AddPic_OnClick(object sender, RoutedEventArgs e)
    {
        ImagePath = string.Empty;
        FileOpenPicker openPicker = new FileOpenPicker();
        openPicker.ViewMode = PickerViewMode.Thumbnail;
        openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;

        openPicker.FileTypeFilter.Clear();
        openPicker.FileTypeFilter.Add(".bmp");
        openPicker.FileTypeFilter.Add(".jpg");
        openPicker.FileTypeFilter.Add(".jpeg");
        openPicker.FileTypeFilter.Add(".png");

        // Launch file open picker and caller app is suspended and may be terminated
        var file = await openPicker.PickSingleFileAsync();

        if (file != null)
        {
            var stream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read);
            var image = new BitmapImage();
            image.SetSource(stream);
            xamlimg.Source = image;
            _myClass.ImageBytes = await App.DataModel.GetBytesAsync(file);

        }
    }

其他课程详情：

public BitmapImage Image
    {
        get
        {
            if (ImageBytes == null)
                return null;
            if (_Image == null)
                _Image = new BitmapImage();
            using (var stream = new InMemoryRandomAccessStream())
            {
                stream.WriteAsync(ImageBytes.AsBuffer()).Completed = (i, j) =>
                {
                    stream.Seek(0);
                    _Image.SetSource(stream);
                };
            }
            return _Image;
        }
    }

    [JsonProperty]
    public byte[] ImageBytes { get; set; }

public async Task<byte[]> GetBytesAsync(StorageFile file)
    {
        byte[] fileBytes = null;
        if (file == null) return null;
        using (var stream = await file.OpenReadAsync())
        {
            fileBytes = new byte[stream.Size];
            using (var reader = new DataReader(stream))
            {
                await reader.LoadAsync((uint) stream.Size);
                reader.ReadBytes(fileBytes);
            }
        }
        return fileBytes;
    }

Answer 1

您可以对其进行解码并将其缩放为更小。因此，一旦您从文件选择器中获得结果，您就可以这样做：

using (IRandomAccessStream fileStream = await result.OpenAsync(FileAccessMode.Read))
{
    BitmapDecoder decoder = await BitmapDecoder.CreateAsync(fileStream);
    using (var encoderStream = new InMemoryRandomAccessStream())
    {
        BitmapEncoder encoder = await BitmapEncoder.CreateForTranscodingAsync(encoderStream, decoder);
        var newHeight = decoder.PixelHeight / 2;
        var newWidth = decoder.PixelWidth / 2;
        encoder.BitmapTransform.ScaledHeight = newHeight;
        encoder.BitmapTransform.ScaledWidth = newWidth;

        await encoder.FlushAsync();

        byte[] pixels = new byte[newWidth * newHeight * 4];

        await encoderStream.ReadAsync(pixels.AsBuffer(), (uint)pixels.Length, InputStreamOptions.None);
}

对于序列化，字节数组像素应该更小，但图像质量会更差。