C# png转ico

/// <summary>
/// Converts a PNG image to a icon (ico)
/// </summary>
/// <param name="inputPath">The input path</param>
/// <param name="outputPath">The output path</param>
/// <param name="size">The size (16x16 px by default)</param>
/// <param name="preserveAspectRatio">Preserve the aspect ratio</param>
/// <returns>Wether or not the icon was succesfully generated</returns>
public static bool ConvertPNGToIcon(string inputPath, string outputPath, int size = 256, bool preserveAspectRatio = true)
{
    using (FileStream inputStream = new FileStream(inputPath, FileMode.Open))
    using (FileStream outputStream = new FileStream(outputPath, FileMode.OpenOrCreate))
    {
        return ConvertToIcon(inputStream, outputStream, size, preserveAspectRatio);
    }
}

/// <summary>
/// Converts a PNG image to a icon (ico)
/// </summary>
/// <param name="input">The input stream</param>
/// <param name="output">The output stream</param>
/// <param name="size">The size (16x16 px by default)</param>
/// <param name="preserveAspectRatio">Preserve the aspect ratio</param>
/// <returns>Wether or not the icon was succesfully generated</returns>
public static bool ConvertPNGToIcon(Stream input, Stream output, int size = 16, bool preserveAspectRatio = false)
{
    Bitmap inputBitmap = (Bitmap)Bitmap.FromStream(input);
    if (inputBitmap != null)
    {
        int width, height;
        if (preserveAspectRatio)
        {
            width = size;
            height = inputBitmap.Height / inputBitmap.Width * size;
        }
        else
        {
            width = height = size;
        }
        Bitmap newBitmap = new Bitmap(inputBitmap, new System.Drawing.Size(width, height));
        if (newBitmap != null)
        {
            // save the resized png into a memory stream for future use
            using (MemoryStream memoryStream = new MemoryStream())
            {
                newBitmap.Save(memoryStream, ImageFormat.Png);

                BinaryWriter iconWriter = new BinaryWriter(output);
                if (output != null && iconWriter != null)
                {
                    // 0-1 reserved, 0
                    iconWriter.Write((byte)0);
                    iconWriter.Write((byte)0);

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

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

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

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

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

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

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

                    // 8-11 size of image data
                    iconWriter.Write((int)memoryStream.Length);

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

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

                    iconWriter.Flush();

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