converting bitmap to byte array c#

Bitmap bmp;
using (var ms = new MemoryStream(imageData))
{
    bmp = new Bitmap(ms);
}

public static class ImageExtensions
{
    public static byte[] ToByteArray(this Image image, ImageFormat format)
    {
        using(MemoryStream ms = new MemoryStream())
        {
            image.Save(ms, format);
            return ms.ToArray();
        }
    }
}

public static byte[] ImageToByte(Image img)
{
    ImageConverter converter = new ImageConverter();
    return (byte[])converter.ConvertTo(img, typeof(byte[]));
}

public static byte[] ImageToByte2(Image img)
{
    using (var stream = new MemoryStream())
    {
        img.Save(stream, System.Drawing.Imaging.ImageFormat.Png);
        return stream.ToArray();
    }
}