旋转Image元素不会在其Source属性中旋转ImageSource。

Rotating the Image element does in no way rotate the ImageSource in its Source property.

要创建旋转的ImageSource，请使用 TransformedBitmap ：

To create a rotated ImageSource, use a TransformedBitmap:

var sourceBitmap = new BitmapImage();

using (var stream = new MemoryStream(ImageSource))
{
    sourceBitmap.BeginInit();
    sourceBitmap.CacheOption = BitmapCacheOption.OnLoad;
    sourceBitmap.StreamSource = stream;
    sourceBitmap.EndInit();
}

// This should be another view model property that the Slider is bound to.
// Only multiples of 90 degrees are valid values.
var rotationAngle = 90d;

var rotation = new RotateTransform(rotationAngle);

var rotatedBitmap = new TransformedBitmap(sourceBitmap, rotation);

为避免您必须创建新来源每次转换的位图，您应该将ImageSource属性的类型从 byte [] 更改为 ImageSource 。

为了将其写回另一个 byte [] ，请使用 BitmapEncoder之一类，例如 PngBitapEncoder 。

In order to write this back into another byte[], use one of the BitmapEncoder classes, e.g. PngBitapEncoder.