A simple script to convert quickly a bunch of png to jpg.

PngToJpg

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Nito.AsyncEx;

namespace PngToJpg
{
	internal class Program
	{
		private static void Main(string[] args)
		{
			AsyncContext.Run(() => MainAsync(args));
		}

		private static async void MainAsync(IEnumerable<string> args)
		{
			var tasks = new Collection<Task>();
			foreach (var arg in args.Where(a => Path.GetExtension(a) != null
				&& Path.GetExtension(a).Equals(".png")))
			{
				tasks.Add(ConvertToJpg(arg));
			}
			await Task.WhenAll(tasks);
		}

		private static Task ConvertToJpg(string path)
		{
			return Task.Run(() =>
			{
				var image = Image.FromFile(path);
				var newPath = Path.ChangeExtension(path, ".jpg");
				using (var b = new Bitmap(image.Width, image.Height))
				{
					b.SetResolution(image.HorizontalResolution, image.VerticalResolution);
					using (var g = Graphics.FromImage(b))
					{
						g.Clear(Color.White);
						g.DrawImageUnscaled(image, 0, 0);
					}
					b.Save(newPath, ImageFormat.Jpeg);
				}
			});
		}
	}
}