A simple class that converts a image to a icon in c# without losing image color data, unlike System.Drawing.Icon; ico with png data requires Windows Vista or above

gistfile1.cs

class PngIconConverter
    {
        /* input image with width = height is suggested to get the best result */
        /* png support in icon was introduced in Windows Vista */
        public static bool Convert(System.IO.Stream input_stream, System.IO.Stream output_stream, int size, bool keep_aspect_ratio = false)
        {
            System.Drawing.Bitmap input_bit = (System.Drawing.Bitmap)System.Drawing.Bitmap.FromStream(input_stream);
            if (input_bit != null)
            {
                int width, height;
                if (keep_aspect_ratio)
                {
                    width = size;
                    height = input_bit.Height / input_bit.Width * size;
                }
                else
                {
                    width = height = size;
                }
                System.Drawing.Bitmap new_bit = new System.Drawing.Bitmap(input_bit, new System.Drawing.Size(width, height));
                if (new_bit != null)
                {
                    // save the resized png into a memory stream for future use
                    System.IO.MemoryStream mem_data = new System.IO.MemoryStream();
                    new_bit.Save(mem_data, System.Drawing.Imaging.ImageFormat.Png);

                    System.IO.BinaryWriter icon_writer = new System.IO.BinaryWriter(output_stream);
                    if (output_stream != null && icon_writer != null)
                    {
                        // 0-1 reserved, 0
                        icon_writer.Write((byte)0);
                        icon_writer.Write((byte)0);

                        // 2-3 image type, 1 = icon, 2 = cursor
                        icon_writer.Write((short)1);

                        // 4-5 number of images
                        icon_writer.Write((short)1);

                        // image entry 1
                        // 0 image width
                        icon_writer.Write((byte)width);
                        // 1 image height
                        icon_writer.Write((byte)height);

                        // 2 number of colors
                        icon_writer.Write((byte)0);

                        // 3 reserved
                        icon_writer.Write((byte)0);

                        // 4-5 color planes
                        icon_writer.Write((short)0);

                        // 6-7 bits per pixel
                        icon_writer.Write((short)32);

                        // 8-11 size of image data
                        icon_writer.Write((int)mem_data.Length);

                        // 12-15 offset of image data
                        icon_writer.Write((int)(6 + 16));

                        // write image data
                        // png data must contain the whole png data file
                        icon_writer.Write(mem_data.ToArray());

                        icon_writer.Flush();

                        return true;
                    }
                }
                return false;
            }
            return false;
        }

        public static bool Convert(string input_image, string output_icon, int size, bool keep_aspect_ratio = false)
        {
            System.IO.FileStream input_stream = new System.IO.FileStream(input_image, System.IO.FileMode.Open);
            System.IO.FileStream output_stream = new System.IO.FileStream(output_icon, System.IO.FileMode.OpenOrCreate);

            bool result = Convert(input_stream, output_stream, size, keep_aspect_ratio);

            input_stream.Close();
            output_stream.Close();

            return result;
        }
    }

@EvertKuijpers Your VB.NET version works excellently; however (with Option Strick On), I had to fix three errors and several naming rule violations.
Added "As Boolean" to the last function.
Changed "offset += imageStreams(index:=i).Length" to "offset += CInt(imageStreams(index:=i).Length)".
Changed "Dim inputBitmap As Drawing.Bitmap = Drawing.Bitmap.FromStream(stream:=input)" to "Dim inputBitmap As Drawing.Bitmap = CType(Drawing.Bitmap.FromStream(stream:=input), Drawing.Bitmap)".

@Amerigoware1 The missing "As Boolean" is an error for sure. Thank you for finding this. Greetz from Tilburg in The Netherlands.