为什么在裁剪图像时我得到裁剪图像的黑色图像？

Question

在form1构造函数中

public Form1()
        {
            InitializeComponent();

            BackColor = Color.LightGreen;
            TransparencyKey = Color.LightGreen;
            this.TopMost = true;
            this.Location = new Point(0, 0);
            timer1.Enabled = true;
        }

然后：

private void Cap()
        {
            countImages++;            
            ScreenCapture sc = new ScreenCapture();            
            Image img = sc.CaptureScreen();
            Bitmap bmp = new Bitmap(img);
            Bitmap source = new Bitmap(this.Width, this.Height);
            Rectangle section = new Rectangle(new Point(source.Width, source.Height), source.Size);
            Bitmap CroppedImage = CropImage(source, section);
            CroppedImage.Save("c:\\temp\\screens\\" + countImages + ".gif", ImageFormat.Gif);
            source.Dispose();  
        }

和

public Bitmap CropImage(Bitmap source, Rectangle section)
        {
            // An empty bitmap which will hold the cropped image
            Bitmap bmp = new Bitmap(section.Width, section.Height);

            Graphics g = Graphics.FromImage(bmp);

            // Draw the given area (section) of the source image
            // at location 0,0 on the empty bitmap (bmp)
            g.DrawImage(source, 0, 0, section, GraphicsUnit.Pixel);

            return bmp;
        }

我保存到硬盘的位图：

CroppedImage.Save("c:\\temp\\screens\\" + countImages + ".gif", ImageFormat.Gif);

他们都是黑色的。 我想从图像中裁剪这部分并将其保存到硬盘中。

屏幕截图示例以及我想从中裁剪的内容： 我用红色圆圈标记了透明的 form1，这就是我想要裁剪 form1 的部分并将其保存为 form1 部分的裁剪图像：

我首先尝试了这个：

private void CaptureDesktop()
        {
            countImages++;
            ScreenCapture sc = new ScreenCapture();                    
            Image img = sc.CaptureScreen();
            Bitmap bmp = new Bitmap(img);            
            Bitmap source = new Bitmap(this.Width, this.Height);
            Rectangle section = new Rectangle(new Point(source.Width, source.Height), source.Size);
            Bitmap CroppedImage = CropImage(bmp, section);
            CroppedImage.Save("c:\\temp\\desktopscreens\\" + countImages + ".gif", ImageFormat.Gif);
        }

但是我得到了这个裁剪的图像结果：奇怪的画中画？

然后我尝试了这段代码：

using (Bitmap bmpScreenCapture = new Bitmap(Screen.PrimaryScreen.Bounds.Width,
                                        Screen.PrimaryScreen.Bounds.Height))
            {
                using (Graphics g = Graphics.FromImage(bmpScreenCapture))
                {

                    g.CopyFromScreen(this.Location.X,
                                   this.Location.Y,
                                   0, 0,
                                   this.Size,
                                   CopyPixelOperation.SourceCopy);


                }

                Rectangle section = new Rectangle(new Point(this.Location.X, this.Location.Y), new Size(this.Width, this.Height));
                Bitmap CroppedImage = CropImage(bmpScreenCapture, section);
                CroppedImage.Save("c:\\temp\\desktopscreens\\1.bmp", ImageFormat.Bmp);


            }

但结果是：

不是我想要的。我只想从整个图像中裁剪 form1 部分。

Answer 1

您执行Bitmap source = new Bitmap(this.Width, this.Height); 这将创建一个黑色图像。

然后你继续裁剪它。那仍然是黑色图像。

然后您继续保存它。那仍然是黑色图像。

也许您的意思是裁剪 Bitmap bmp 或 Image img，而不是 Bitmap source。我不知道Bitmap source 是什么意思。

Answer 2

试试这个（来自Capture the screen shot using .NET的一些代码）

 private void Cap()
    {
        using (Bitmap bmpScreenCapture = new Bitmap(Screen.PrimaryScreen.Bounds.Width,
                                        Screen.PrimaryScreen.Bounds.Height))
        {
            using (Graphics g = Graphics.FromImage(bmpScreenCapture))
            {

                g.CopyFromScreen(this.Location.X,
                               this.Location.Y,
                               0, 0,
                               this.Size,
                               CopyPixelOperation.SourceCopy);


            }

            Rectangle section = new Rectangle(new Point(this.Location.X, this.Location.Y), new Size(this.Width, this.Height));
            Bitmap CroppedImage = CropImage(bmpScreenCapture, section);
            CroppedImage.Save("c:\\temp\\screens\1.bmp", ImageFormat.Bmp);


        }




    }

    public Bitmap CropImage(Bitmap source, Rectangle section)
    {
        // An empty bitmap which will hold the cropped image
        Bitmap bmp = new Bitmap(section.Width, section.Height);

        Graphics g = Graphics.FromImage(bmp);

        // Draw the given area (section) of the source image
        // at location 0,0 on the empty bitmap (bmp)
        g.DrawImage(source, 0, 0, section, GraphicsUnit.Pixel);

        return bmp;
    }