将位图（例如，从剪贴板内容）转换为 PNG

IRandomAccessStreamReference bitmap = GetBitmap();
IRandomAccessStreamWithContentType stream = await bitmap.OpenReadAsync();
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
var pixels = await decoder.GetPixelDataAsync();
var outStream = new InMemoryRandomAccessStream();

// Create encoder for PNG
var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, outStream);

// Get pixel data from decoder and set them for encoder
encoder.SetPixelData(decoder.BitmapPixelFormat,
                     BitmapAlphaMode.Ignore, // Alpha is not used
                     decoder.OrientedPixelWidth,
                     decoder.OrientedPixelHeight,
                     decoder.DpiX, decoder.DpiY,
                     pixels.DetachPixelData());

await encoder.FlushAsync(); // Write data to the stream

// Here you can use your stream