PNGEncoder always premultiplies alpha when loading or saving

[JimmyDirect]

Hi, I guess this is by design, but can someone help me out to configure the PNG Encoder to not automatically premultiply alpha when loading/saving, so that I get exactly the same pixels back that I have written.

In the following example the asserts at the end fail but I dont fully understand why:

        const string filename = "test.png";

        [TestMethod]
        public void Premulti()
        {
            SKBitmap bmp = new SKBitmap(16, 16, SKColorType.Bgra8888, SKAlphaType.Unpremul);
            bmp.SetPixel(0, 0, new SKColor(red: 255, green: 17, blue: 99, alpha: 100));
            byte[] bytes = bmp.Bytes;

            Assert.AreEqual(99, bytes[0]);
            Assert.AreEqual(17, bytes[1]);
            Assert.AreEqual(255, bytes[2]);
            Assert.AreEqual(100, bytes[3]);

            using var data = bmp.Encode(SKEncodedImageFormat.Png, 100);
            using var stream = File.OpenWrite(filename);
            data.SaveTo(stream);
            stream.Close();


            var image = SKImage.FromEncodedData(filename);
            var bmp2 = SKBitmap.FromImage(image);

            bytes = bmp2.Bytes;

            Assert.AreEqual(99, bytes[0]); // is actually 39 = 99 * 100 /255
            Assert.AreEqual(17, bytes[1]); // is actually 7 = 17 * 100 /255
            Assert.AreEqual(255, bytes[2]); // is actually 100 = 255 * 100 / 255
            Assert.AreEqual(100, bytes[3]);
        }