自己写了个截图工具

很简单，就是先全屏截图，然后再按需要裁剪就可以了。

所以，首先要获取桌面的大小，代码如下：

    public class PrimaryScreen
    {
        #region Win32 API
        [DllImport("user32.dll")]
        static extern IntPtr GetDC(IntPtr ptr);
        [DllImport("gdi32.dll")]
        static extern int GetDeviceCaps(
        IntPtr hdc, // handle to DC
        int nIndex // index of capability
        );
        [DllImport("user32.dll", EntryPoint = "ReleaseDC")]
        static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDc);
        #endregion
        #region DeviceCaps常量
        const int HORZRES = 8;
        const int VERTRES = 10;
        const int LOGPIXELSX = 88;
        const int LOGPIXELSY = 90;
        const int DESKTOPVERTRES = 117;
        const int DESKTOPHORZRES = 118;
        #endregion
        #region 属性
        /// <summary>
        /// 获取屏幕分辨率当前物理大小
        /// </summary>
        public static Size WorkingArea
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                Size size = new Size();
                size.Width = GetDeviceCaps(hdc, HORZRES);
                size.Height = GetDeviceCaps(hdc, VERTRES);
                ReleaseDC(IntPtr.Zero, hdc);
                return size;
            }
        }
        /// <summary>
        /// 当前系统DPI_X 大小 一般为96
        /// </summary>
        public static int DpiX
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                int DpiX = GetDeviceCaps(hdc, LOGPIXELSX);
                ReleaseDC(IntPtr.Zero, hdc);
                return DpiX;
            }
        }
        /// <summary>
        /// 当前系统DPI_Y 大小 一般为96
        /// </summary>
        public static int DpiY
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                int DpiX = GetDeviceCaps(hdc, LOGPIXELSY);
                ReleaseDC(IntPtr.Zero, hdc);
                return DpiX;
            }
        }
        /// <summary>
        /// 获取真实设置的桌面分辨率大小
        /// </summary>
        public static Size DESKTOP
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                Size size = new Size();
                size.Width = GetDeviceCaps(hdc, DESKTOPHORZRES);
                size.Height = GetDeviceCaps(hdc, DESKTOPVERTRES);
                ReleaseDC(IntPtr.Zero, hdc);
                return size;
            }
        }

        /// <summary>
        /// 获取宽度缩放百分比
        /// </summary>
        public static float ScaleX
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                int t = GetDeviceCaps(hdc, DESKTOPHORZRES);
                int d = GetDeviceCaps(hdc, HORZRES);
                float ScaleX = (float)GetDeviceCaps(hdc, DESKTOPHORZRES) / (float)GetDeviceCaps(hdc, HORZRES);
                ReleaseDC(IntPtr.Zero, hdc);
                return ScaleX;
            }
        }
        /// <summary>
        /// 获取高度缩放百分比
        /// </summary>
        public static float ScaleY
        {
            get
            {
                IntPtr hdc = GetDC(IntPtr.Zero);
                float ScaleY = (float)(float)GetDeviceCaps(hdc, DESKTOPVERTRES) / (float)GetDeviceCaps(hdc, VERTRES);
                ReleaseDC(IntPtr.Zero, hdc);
                return ScaleY;
            }
        }
        #endregion
    }

使用 PrimaryScreen.DESKTOP 就可以获取桌面分辨率的大小了，有了这个大小，就可以开始全屏截图了，代码如下：

public class ImageHelper
    {
        /// <summary>
        /// 截取全屏
        /// </summary>
        /// <returns></returns>
        public static Bitmap GetScreen()
        {
            Size ScreenSize = PrimaryScreen.DESKTOP;
            Bitmap bmp = new Bitmap(ScreenSize.Width, ScreenSize.Height);
            using (Graphics g = Graphics.FromImage(bmp))
                g.CopyFromScreen(0, 0, 0, 0, new Size(ScreenSize.Width, ScreenSize.Height));
            return bmp;
        }

        /// <summary>
        /// 图像明暗调整
        /// </summary>
        /// <param name="b">原始图</param>
        /// <param name="degree">亮度[-255, 255]</param>
        public static void Lighten(Bitmap b, int degree)
        {
            if (b == null)
            {
                //return null;
                return;
            }

            if (degree < -255) degree = -255;
            if (degree > 255) degree = 255;

            try
            {

                int width = b.Width;
                int height = b.Height;

                int pix = 0;

                BitmapData data = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

                unsafe
                {
                    byte* p = (byte*)data.Scan0;
                    int offset = data.Stride - width * 3;
                    for (int y = 0; y < height; y++)
                    {
                        for (int x = 0; x < width; x++)
                        {
                            // 处理指定位置像素的亮度
                            for (int i = 0; i < 3; i++)
                            {
                                pix = p[i] + degree;

                                if (degree < 0) p[i] = (byte)Math.Max(0, pix);
                                if (degree > 0) p[i] = (byte)Math.Min(255, pix);

                            } // i
                            p += 3;
                        } // x
                        p += offset;
                    } // y
                }

                b.UnlockBits(data);

                //return b;
            }
            catch
            {
                //return null;
            }

        } // end of Lighten
    }

调用 ImageHelper.GetScreen() 即可以获取全屏截图

再然后，为了实现区域截图，我们需要把全屏截图放到一个窗体里面进行裁剪，弹出裁剪窗体的代码如下：

private void button1_Click(object sender, EventArgs e)
{
    this.Opacity = 0; //先隐藏自己
    Bitmap bitmap = ImageHelper.GetScreen(); //截取全屏
    GetScreenForm frm = new GetScreenForm(bitmap); //准备区域截图
    frm.ShowDialog(); //弹出区域截图界面
    this.Opacity = 1; //显示自己
}

区域截图的代码有点多，无非就是鼠标按下、移动、松开的相关处理，以对全屏截图进行裁剪处理，代码如下：

    public partial class GetScreenForm : Form
    {
        /// <summary>
        /// 亮图（原图）
        /// </summary>
        public Bitmap bitmap { get; set; }

        /// <summary>
        /// 暗图
        /// </summary>
        public Bitmap bitmap2 { get; set; }

        /// <summary>
        /// 屏幕的宽
        /// </summary>
        public int W { get; set; }
        /// <summary>
        /// 屏幕的高
        /// </summary>
        public int H { get; set; }
        /// <summary>
        /// 适用于高DPI的宽度
        /// </summary>
        public int W2 { get; set; }
        /// <summary>
        /// 适用于高DPI的高度
        /// </summary>
        public int H2 { get; set; }

        Graphics g;
        Bitmap cache;
        Graphics gMain;

        /// <summary>
        /// 构造方法
        /// </summary>
        public GetScreenForm(Bitmap bitmap)
        {
            //亮图 （也就是原图）
            this.bitmap = bitmap;
            this.W = bitmap.Width;
            this.H = bitmap.Height;

            //暗图
            this.bitmap2 = new Bitmap(bitmap.Width, bitmap.Height);
            using (Graphics g = Graphics.FromImage(bitmap2))
                g.DrawImage(bitmap, 0, 0);
            ImageHelper.Lighten(bitmap2, -100);
            //求出适用于高DPI的宽和高
            W2 = (int)(bitmap2.Width * PrimaryScreen.ScaleX);
            H2 = (int)(bitmap2.Height * PrimaryScreen.ScaleY);
            //初始化
            InitializeComponent();
            this.Width = (int)(this.W / PrimaryScreen.ScaleX);
            this.Height = (int)(this.H / PrimaryScreen.ScaleY);
            //绘图相关
            cache = new Bitmap(this.W, this.H);
            gMain = this.CreateGraphics();
            g = Graphics.FromImage(cache);
        }

        /// <summary>
        /// 双击关闭
        /// </summary>
        protected override void OnDoubleClick(EventArgs e)
        {
            //获取截图 
            if (SX > int.MinValue && SY > int.MinValue)
            {
                //获取区域
                int x1 = SX, x2 = SX + SW;
                if (x1 > x2) { x2 = x1 + x2; x1 = x2 - x1; x2 = x2 - x1; };
                int y1 = SY, y2 = SY + SH;
                if (y1 > y2) { y2 = y1 + y2; y1 = y2 - y1; y2 = y2 - y1; };
                //截图
                Bitmap bmp = new Bitmap(x2 - x1, y2 - y1);
                Graphics g6 = Graphics.FromImage(bmp);
                g6.DrawImage(bitmap,
                    new Rectangle(0, 0, bmp.Width, bmp.Height),
                    new Rectangle((int)(x1 * PrimaryScreen.ScaleX), (int)(y1 * PrimaryScreen.ScaleY), (int)((x2 - x1) * PrimaryScreen.ScaleX), (int)((y2 - y1) * PrimaryScreen.ScaleY)),
                    GraphicsUnit.Pixel);
                bmp.Save("x.jpg", ImageFormat.Jpeg);
            }
            this.Close();
        }

        private void GetScreenForm_Load(object sender, EventArgs e)
        {

        }

        protected override void OnShown(EventArgs e)
        {
            DrawForm();
        }

        void DrawForm()
        {
            //画暗图
            g.DrawImage(bitmap2,
                new Rectangle(0, 0, W, H),   //目标
                new Rectangle(0, 0, W2, H2), //源
                GraphicsUnit.Pixel);

            //画亮图
            if (SX > int.MinValue && SY > int.MinValue)
            {
                g.DrawImage(bitmap,
                    new Rectangle(SX, SY, SW, SH),
                    new Rectangle((int)(SX * PrimaryScreen.ScaleX), (int)(SY * PrimaryScreen.ScaleY), (int)(SW * PrimaryScreen.ScaleX), (int)(SH * PrimaryScreen.ScaleY)),
                    GraphicsUnit.Pixel);
                //new Rectangle(SX, SY, SW, SH),   //目标
                //new Rectangle(SX, SY, SW, SH),   //源
                //GraphicsUnit.Pixel);
            }

            //翻转
            gMain.DrawImage(cache, 0, 0);
        }

        /// <summary>
        /// 选择的区域
        /// </summary>
        public int SX { get; set; } = int.MinValue;
        public int SY { get; set; } = int.MinValue;
        public int SW { get; set; }
        public int SH { get; set; }

        /// <summary>
        /// 工作类型 0未工作 1画框 2移框
        /// </summary>
        public int WorkType { get; set; }

        /// <summary>
        /// 移动的起点
        /// </summary>
        public int MoveX { get; set; }
        public int MoveY { get; set; }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            //判断是不是点击在框里
            bool inside = false;
            if (SX > int.MinValue && SY > int.MinValue)
            {
                int x1 = SX, x2 = SX + SW;
                if (x1 > x2) { x2 = x1 + x2; x1 = x2 - x1; x2 = x2 - x1; };
                int y1 = SY, y2 = SY + SH;
                if (y1 > y2) { y2 = y1 + y2; y1 = y2 - y1; y2 = y2 - y1; };
                if (e.X > x1 && e.X < x2
                    && e.Y > y1 && e.Y < y2)
                {
                    inside = true;
                }
            }
            if (inside)
            {
                //在框里，则进行移框
                this.MoveX = e.X;
                this.MoveY = e.Y;
                this.WorkType = 2;
                DrawForm();
            }
            else
            {
                //在框外，则重新画框
                this.SX = e.X;
                this.SY = e.Y;
                this.SW = 0;
                this.SH = 0;
                this.WorkType = 1;
                DrawForm();
            }
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                if (this.WorkType == 1)
                {
                    //画框
                    this.SW = e.X - this.SX;
                    this.SH = e.Y - this.SY;
                }
                else
                {
                    //移框
                    this.SX += e.X - this.MoveX;
                    this.SY += e.Y - this.MoveY;
                    this.MoveX = e.X;
                    this.MoveY = e.Y;
                }
                DrawForm();
            }
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            if (this.WorkType == 1)
            {
                this.SW = e.X - this.SX;
                this.SH = e.Y - this.SY;
            }
            this.WorkType = 0;
            DrawForm();
        }
    }

提供源代码给大家玩玩，点这里下载源代码。