public byte[] GetPixelBytes()

Return Value

• Works on bitmaps of any format.
• For uncompressed texture formats, the size of the array is SizeInPixels.Width * SizeInPixels.Height * (bytes per pixel). The number of bytes per pixel is determined by Format. For a CanvasBitmap with the default format of DirectXPixelFormat.B8G8R8A8UIntNormalized this is 4.
• For block compressed texture formats, the size of the array is SizeInPixels.Width * SizeInPixels.Height * (bytes per block) / 16. See Bitmap block compression page for more information.

Reference