wpf-截取屏幕上指定区域

private void OnMenuExportGraph(object sender, RoutedEventArgs e)
{
    if (_isLoaded == false)
    {
        MessageBox.Show("请先导入文件", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
    }
    else
    {
        int w = (int)this.Width;
        int h = (int)this.Height;
        // 自定义的处理方法
        int imgWidth = (int)(...);
        int imgHeight = (int)(...);
        //Bitmap bit = new Bitmap(w, h);//实例化一个和窗体一样大的bitmap
        Bitmap bit = new Bitmap(imgWidth, imgHeight);
        Graphics g = Graphics.FromImage(bit);
        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;//质量设为最高
        g.CopyFromScreen((int)(this.Left+10), (int)(this.Top+65), (int)(0), (int)(0), new System.Drawing.Size(imgWidth, imgHeight));
        // 指定存储位置
        var dialog = new SaveFileDialog();
        if (dialog.ShowDialog().GetValueOrDefault()) {
            string filePath = dialog.FileName;
            try
            {
                bit.Save(filePath);//默认保存格式为PNG，保存成jpg格式质量不是很好
                MessageBox.Show("OK");
            }
            catch (Exception) {
                MessageBox.Show("请检查存储位置", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }                   
    }
}

第一次写成这样：Bitmap bit = new Bitmap(w, h)，导致打开时总有两条线在角落里。改变大小时，线段时有时无。后来发现是透明的背景，如下图。

把bit改小一些就可以了。