ScreenCapture/ScreenCapture.cs

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows.Forms;
using static ScreenCapture.NativeMethods;

namespace ScreenCapture
{
    sealed class ScreenCapture
    {
        #region Singleton
        private static ScreenCapture instance;

        public static ScreenCapture Instance
        {
            get
            {
                instance = instance ?? new ScreenCapture();
                return instance;
            }
        }
        #endregion

        private readonly static EncoderParameters encParamsJPG = new EncoderParameters();
        private readonly static ImageCodecInfo codecJPG = GetEncoderInfo(ImageFormat.Jpeg);
        private readonly static ImageCodecInfo codecPNG = GetEncoderInfo(ImageFormat.Png);

        public string FileName { get; private set; }
        public MemoryStream Stream { get; private set; }

        private ScreenCapture()
        {
            encParamsJPG.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90L);
        }

        public void CaptureWindow()
        {
            Capture(CurrentWindow);
        }

        public void Release()
        {
            Stream.Close();
            Stream.Dispose();
            FileName = null;
        }

        private Rectangle CurrentWindow
        {
            get
            {
                IntPtr window = GetForegroundWindow();
                Rect rect = new Rect();
                GetWindowRect(window, ref rect);
                StringBuilder sb = new StringBuilder(255);
                GetWindowText(window, sb, sb.Capacity);
                FileName = sanitizeFileName(sb.ToString()) + "_" + DateTime.Now.Ticks + ".";
                return new Rectangle(rect.Left, rect.Top, rect.Right - rect.Left, rect.Bottom - rect.Top);
            }
        }

        private void Capture(Rectangle bounds)
        {
            using (Bitmap image = new Bitmap(bounds.Width, bounds.Height))
            {
                using (Graphics g = Graphics.FromImage(image))
                {
                    g.CopyFromScreen(new Point(bounds.Left, bounds.Top), Point.Empty, bounds.Size);
                }
                Stream = BestStream(image);
                Stream.Seek(0, SeekOrigin.Begin);
            }
        }

        private MemoryStream BestStream(Bitmap image)
        {
            MemoryStream png = WriteToMemory(image, codecPNG, null);
            MemoryStream jpg = WriteToMemory(image, codecJPG, encParamsJPG);

            if (png.Length <= jpg.Length)
            {
                FileName += "png";
                jpg.Close();
                jpg.Dispose();
                return png;
            }
            else
            {
                FileName += "jpg";
                png.Close();
                png.Dispose();
                return jpg;
            }
        }

        private static MemoryStream WriteToMemory(Bitmap image, ImageCodecInfo imageCodeInfo, EncoderParameters encoderParam)
        {
            MemoryStream mt = new MemoryStream();
            image.Save(mt, imageCodeInfo, encoderParam);
            return mt;
        }

        private static ImageCodecInfo GetEncoderInfo(ImageFormat format)
        {
            return ImageCodecInfo.GetImageEncoders().First(codec =>
            {
                return codec.FormatID == format.Guid;
            });
        }


        private static string sanitizeFileName(string str)
        {
            return Regex.Replace(String.Join("_", str.Split(Path.GetInvalidFileNameChars(), StringSplitOptions.RemoveEmptyEntries)).TrimEnd('.'), @"[^\u0000-\u007F]", string.Empty);
        }
    }
}