以编程方式获取页面的屏幕截图

Question

我正在编写一个专门的爬虫和解析器供内部使用,我需要能够截取网页的截图,以检查整个过程中使用的颜色.该程序将接收大约十个网址,并将其保存为位图图像.

从那里我计划使用LockBits来创建图像中五种最常用颜色的列表.据我所知,这是获取网页中使用的颜色的最简单方法,但如果有更简单的方法,请提出您的建议.

无论如何,在我看到价格标签之前,我打算使用ACA WebThumb ActiveX Control.我也是C#的新手,只用了几个月.有没有解决我的网页截图以提取配色方案的问题？

Answer 1

一种快速而肮脏的方法是使用WinForms WebBrowser控件并将其绘制到位图.在独立控制台应用程序中执行此操作有点棘手,因为您必须了解在使用基本异步编程模式时托管STAThread控件的含义.但这是一个工作概念证明,它将网页捕获到800x600 BMP文件:

namespace WebBrowserScreenshotSample
{
    using System;
    using System.Drawing;
    using System.Drawing.Imaging;
    using System.Threading;
    using System.Windows.Forms;

    class Program
    {
        [STAThread]
        static void Main()
        {
            int width = 800;
            int height = 600;

            using (WebBrowser browser = new WebBrowser())
            {
                browser.Width = width;
                browser.Height = height;
                browser.ScrollBarsEnabled = true;

                // This will be called when the page finishes loading
                browser.DocumentCompleted += Program.OnDocumentCompleted;

                browser.Navigate("https://stackoverflow.com/");

                // This prevents the application from exiting until
                // Application.Exit is called
                Application.Run();
            }
        }

        static void OnDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            // Now that the page is loaded, save it to a bitmap
            WebBrowser browser = (WebBrowser)sender;

            using (Graphics graphics = browser.CreateGraphics())
            using (Bitmap bitmap = new Bitmap(browser.Width, browser.Height, graphics))
            {
                Rectangle bounds = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
                browser.DrawToBitmap(bitmap, bounds);
                bitmap.Save("screenshot.bmp", ImageFormat.Bmp);
            }

            // Instruct the application to exit
            Application.Exit();
        }
    }
}

要编译它,请创建一个新的控制台应用程序,并确保为System.Drawing和添加程序集引用System.Windows.Forms.

更新:我重写了代码,以避免使用hacky轮询WaitOne/DoEvents模式.此代码应更接近以下最佳实践.

更新2:您表明要在Windows窗体应用程序中使用它.在这种情况下,忘记动态创建WebBrowser控件.你想要的是WebBrowser在你的表单上创建一个隐藏的(Visible = false)实例,并按照我上面显示的方式使用它.这是另一个示例,它显示了带有文本框(webAddressTextBox),按钮(generateScreenshotButton)和隐藏浏览器(webBrowser)的表单的用户代码部分.当我正在研究这个时,我发现了一个我之前没有处理过的特性 - DocumentCompleted事件实际上可以根据页面的性质多次提升.此示例应该可以正常工作,您可以扩展它以执行任何操作:

namespace WebBrowserScreenshotFormsSample
{
    using System;
    using System.Drawing;
    using System.Drawing.Imaging;
    using System.IO;
    using System.Windows.Forms;

    public partial class MainForm : Form
    {
        public MainForm()
        {
            this.InitializeComponent();

            // Register for this event; we'll save the screenshot when it fires
            this.webBrowser.DocumentCompleted += 
                new WebBrowserDocumentCompletedEventHandler(this.OnDocumentCompleted);
        }

        private void OnClickGenerateScreenshot(object sender, EventArgs e)
        {
            // Disable button to prevent multiple concurrent operations
            this.generateScreenshotButton.Enabled = false;

            string webAddressString = this.webAddressTextBox.Text;

            Uri webAddress;
            if (Uri.TryCreate(webAddressString, UriKind.Absolute, out webAddress))
            {
                this.webBrowser.Navigate(webAddress);
            }
            else
            {
                MessageBox.Show(
                    "Please enter a valid URI.",
                    "WebBrowser Screenshot Forms Sample",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Exclamation);

                // Re-enable button on error before returning
                this.generateScreenshotButton.Enabled = true;
            }
        }

        private void OnDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            // This event can be raised multiple times depending on how much of the
            // document has loaded, if there are multiple frames, etc.
            // We only want the final page result, so we do the following check:
            if (this.webBrowser.ReadyState == WebBrowserReadyState.Complete &&
                e.Url == this.webBrowser.Url)
            {
                // Generate the file name here
                string screenshotFileName = Path.GetFullPath(
                    "screenshot_" + DateTime.Now.Ticks + ".png");

                this.SaveScreenshot(screenshotFileName);
                MessageBox.Show(
                    "Screenshot saved to '" + screenshotFileName + "'.",
                    "WebBrowser Screenshot Forms Sample",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Information);

                // Re-enable button before returning
                this.generateScreenshotButton.Enabled = true;
            }
        }

        private void SaveScreenshot(string fileName)
        {
            int width = this.webBrowser.Width;
            int height = this.webBrowser.Height;
            using (Graphics graphics = this.webBrowser.CreateGraphics())
            using (Bitmap bitmap = new Bitmap(width, height, graphics))
            {
                Rectangle bounds = new Rectangle(0, 0, width, height);
                this.webBrowser.DrawToBitmap(bitmap, bounds);
                bitmap.Save(fileName, ImageFormat.Png);
            }
        }
    }
}

Answer 2

https://www.url2png.com/docs是一个很好的.他们有免费套餐.

您需要使用HttpWebRequest下载图像的二进制文件.这是一个例子:

HttpWebRequest request = HttpWebRequest.Create("https://[url]") as HttpWebRequest;
Bitmap bitmap;
using (Stream stream = request.GetResponse().GetResponseStream())
{
    bitmap = new Bitmap(stream);
}
// now that you have a bitmap, you can do what you need to do...

要生成URL ...

HttpWebRequest request = HttpWebRequest.Create("https://[url]") as HttpWebRequest;
Bitmap bitmap;
using (Stream stream = request.GetResponse().GetResponseStream())
{
    bitmap = new Bitmap(stream);
}
// now that you have a bitmap, you can do what you need to do...

Answer 3

这个问题很老但是,你也可以使用nuget package Freezer.它是免费的,使用最近的Gecko webbrowser(支持HTML5和CSS3)并且只能在一个dll中使用.

var screenshotJob = ScreenshotJobBuilder.Create("https://google.com")
              .SetBrowserSize(1366, 768)
              .SetCaptureZone(CaptureZone.FullPage) 
              .SetTrigger(new WindowLoadTrigger()); 

 System.Drawing.Image screenshot = screenshotJob.Freeze();

Answer 4

有一个很棒的基于Webkit的浏览器PhantomJS允许从命令行执行任何JavaScript.

从http://phantomjs.org/download.html安装它, 并从命令行执行以下示例脚本:

./phantomjs ../examples/rasterize.js http://www.panoramio.com/photo/76188108 test.jpg

它将在JPEG文件中创建给定页面的屏幕截图.这种方法的好处是您不依赖任何外部提供商,并且可以轻松自动化大量截屏.

Answer 5

我使用了 WebBrowser，但它对我来说并不完美，特别是当需要等待 JavaScript 渲染完成时。我尝试了一些 Api(s) 并发现Selenium，Selenium 最重要​​的是，它不需要 STAThread 并且可以在简单的控制台应用程序和服务中运行。

试一试 ：

class Program
{
    static void Main()
    {
        var driver = new FirefoxDriver();

        driver.Navigate()
            .GoToUrl("http://stackoverflow.com/");

        driver.GetScreenshot()
            .SaveAsFile("stackoverflow.jpg", ImageFormat.Jpeg);

        driver.Quit();
    }
}