[UWP]从 BitmapImage 调整大小、压缩并获取 base64 字符串

Question

这是我的第一个主题！我正在重写我在 UWP 中使用 Silverlight 8 (WP8) 开发的应用程序。我从 BitmapImage 获取 base64 编码字符串时遇到问题。我工作了很多天都找不到解决方案:-( .

总之，我需要： - 从设备库中选择图像 - 将所选图像剪切为 1 兆像素（1024* 1024） - 压缩所选图像 -从压缩图像中获取base64编码字符串

我的 Silverlight 8 代码（工作）：

Private Sub attachButtonHan_Click(sender As Object, e As EventArgs)
Dim photoChooserTaskAttach As Microsoft.Phone.Tasks.PhotoChooserTask
photoChooserTaskAttach = New Microsoft.Phone.Tasks.PhotoChooserTask With {.ShowCamera = True, .PixelHeight = 1024, .PixelWidth = 1024} ' how can i cut selected image from fileOpenPicker in UWP???
AddHandler photoChooserTaskAttach.Completed, AddressOf photoChooserTaskAttach_Completed
photoChooserTaskAttach.Show()
End Sub

Private Sub photoChooserTaskAttach_Completed(sender As Object, e As Microsoft.Phone.Tasks.PhotoResult)
If e.TaskResult = TaskResult.OK Then
Dim bmp As New System.Windows.Media.Imaging.BitmapImage
bmp.CreateOptions = BitmapCreateOptions.BackgroundCreation
bmp.CreateOptions = BitmapCreateOptions.DelayCreation
bmp.DecodePixelWidth = 1024
bmp.DecodePixelHeight = 1024
bmp.SetSource(e.ChosenPhoto)
Dim ms As New MemoryStream
Dim wbc As New System.Windows.Media.Imaging.WriteableBitmap(bmp)
wbc.SaveJpeg(ms, bmp.PixelWidth, bmp.PixelHeight, 0, 70) ' in UWP SaveJpeg Extension is missing...??
Dim result As Byte() = ms.ToArray()
Dim base64 As String = System.Convert.ToBase64String(result)
End If
End Sub

我的 UWP 代码（不起作用）：

Private Async Sub ButtonSelectImgSmp_Click(sender As Object, e As RoutedEventArgs) Handles ButtonSelectImgSmp.Click
Dim openPicker As New FileOpenPicker()
openPicker.ViewMode = PickerViewMode.Thumbnail
openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary
openPicker.FileTypeFilter.Add(".jpg")
openPicker.FileTypeFilter.Add(".jpeg")
openPicker.FileTypeFilter.Add(".png")
Dim file As StorageFile = Await openPicker.PickSingleFileAsync()

如何将所选图像剪切为 1024*1024？

If file IsNot Nothing Then
Dim streambmp = Await file.OpenAsync(Windows.Storage.FileAccessMode.Read)
Dim btmapImage = New Windows.UI.Xaml.Media.Imaging.BitmapImage()
btmapImage.DecodePixelHeight = 1024
btmapImage.DecodePixelWidth = 1024
Await btmapImage.SetSourceAsync(streambmp)
Dim ms As New MemoryStream

'  Dim wbc As New WriteableBitmap(bmp) ' Error
'  wbc.SaveJpeg(ms, bmp.PixelWidth, bmp.PixelHeight, 0, 70) 

' Error (missing savejpeg extension)   

Dim result As Byte() = ms.ToArray() 
Dim base64 As String = System.Convert.ToBase64String(result)

End If
End Sub

谢谢！！

Answer 1

在 UWP 中，您可以使用 BitmapDecoder 和 BitmapTransform 来裁剪图像。以下是关于将所选图像裁剪为 100x100 的简单示例。

Private Async Sub Button_Click(sender As Object, e As RoutedEventArgs)
    Dim openPicker As New FileOpenPicker()
    openPicker.ViewMode = PickerViewMode.Thumbnail
    openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary
    openPicker.FileTypeFilter.Add(".jpg")
    openPicker.FileTypeFilter.Add(".jpeg")
    openPicker.FileTypeFilter.Add(".png")
    Dim file As StorageFile = Await openPicker.PickSingleFileAsync()

    Dim stream As IRandomAccessStream = Await file.OpenAsync(FileAccessMode.Read)

    Dim decoder As BitmapDecoder = Await BitmapDecoder.CreateAsync(stream)
    Dim transform As BitmapTransform = New BitmapTransform()
    Dim bounds As BitmapBounds = New BitmapBounds()
    bounds.X = 0
    bounds.Y = 0
    bounds.Height = 100
    bounds.Width = 100
    transform.Bounds = bounds

    Dim pix As PixelDataProvider = Await decoder.GetPixelDataAsync(
        BitmapPixelFormat.Bgra8,
        BitmapAlphaMode.Straight,
        transform,
        ExifOrientationMode.IgnoreExifOrientation,
        ColorManagementMode.ColorManageToSRgb)
    Dim pixels As Byte() = pix.DetachPixelData()

    Dim cropBmp As WriteableBitmap = New WriteableBitmap(100, 100)
    Dim pixStream As Stream = cropBmp.PixelBuffer.AsStream()
    pixStream.Write(pixels, 0, 100 * 100 * 4)

    'Image control used to display the image
    img.Source = cropBmp

    Dim base64 As String = Convert.ToBase64String(pixels)
End Sub

PixelDataProvider.DetachPixelData 方法返回内部存储的像素数据。您可以使用它来获取base64字符串。

这是MSDN上的官方How to crop bitmap in a Windows Store app示例，您可以参考。