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I have code that allows the user to select an image using file picker & I convert the image to a byte array so that it can be serialized. When viewing the collection of images, if I have too many, the app crashes & will not load. When I debug using visual studios it runs fines but takes a long time to load the images. I believe it times out because it's taking to long to load. After obtaining the storage file. How do I lower the quality of the BitmapImage so that when serialized it doesn't take as long to load?

 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);

        }
    }

Other Class details:

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;
    }
4

1 回答 1

7

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，您可以执行以下操作：

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);
}

然后字节数组像素应该更小以进行序列化，但图像质量会更差。

于 2015-12-19T00:58:17.773 回答