Using WebRequest to save URL as Image thumbnail in VB.NET

Question

I'm trying to write a simple routine where I pass it a URL and it goes and renders the content of the webresponse as a jpg. I found a solution somehwere in C# and ported it to vb.net, however when I run it, it throws an argumentexception "parameter is not valid" when trying to instantiate the image. Can someone take a look at the following code and let me know if I'm on the right track?

Sub SaveUrl(ByVal aUrl As String)
    Dim response As WebResponse
    Dim remoteStream As Stream
    Dim readStream As StreamReader
    Dim request As WebRequest = WebRequest.Create(aUrl)
    response = request.GetResponse
    remoteStream = response.GetResponseStream
    readStream = New StreamReader(remoteStream)
    Dim img As System.Drawing.Image = System.Drawing.Image.FromStream(remoteStream)
    img.Save(aUrl & ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg)
    response.Close()
    remoteStream.Close()
    readStream.Close()
End Sub

To Clarify: Yes, I know i need a LOT more code to accomplish what I want to do, which is to render/take a screen capture of a URL (html, images, all the markup, everything) and save it as a jpg thumbnail.

If you've used Google Chrome, you've seen the launch page that has thumbnails of all the sites you use frequently. Something like that.

Update: Ok I've found commercial paid products to accomplish this, like http://www.websitesscreenshot.com/Index.html but no open source implementations.

I don't quite understand what you're trying to accomplish. Download an image and converting it to jpeg? — Mauricio Scheffer
– Mauricio Scheffer, Commented Dec 18, 2008 at 22:23
He is trying to get a image of the website. url converted to an image. So if he would use : stackoverflow.com this will produce an image of stackoverflow main page in a jpeg format. — Patrick Desjardins
– Patrick Desjardins, Commented Dec 19, 2008 at 17:52

Joel Coehoorn · Accepted Answer · 2008-12-18 22:23:08Z

3

Just because the Image class has a .FromStream() method doesn't mean that any stream is a valid image, and the html response from a web server certainly would not be a valid image. Rendering a web page is not a "simple routine". There's a lot that goes into it.

You might try using the WebBrowser control, since that can do a lot of the work for you.

answered Dec 18, 2008 at 22:23

Joel Coehoorn

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Konrad Rudolph · Accepted Answer · 2008-12-18 23:03:35Z

3

Well, either:

My.Computer.Network.DownloadFile("http://example.com/file.jpeg", "local.jpeg")

Or, to create a thumbnail:

Using wc As New Net.WebClient()
    Dim img = Image.FromStream(wc.OpenRead("http://example.com/file"))
    img.GetThumbnailImage(32, 32, Function() False, Nothing).Save("c:\local.jpg")
End Using

… maybe add some error handling. ;-)

answered Dec 18, 2008 at 23:03

Konrad Rudolph

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2 Comments

Joel Coehoorn Over a year ago

I get the impression that he's downloading an html page rather than an image file, and want a thumbnail of the html page.

Konrad Rudolph Over a year ago

@Joel, yes I've now read the clarification as well. I posted my code before that, since it's basically was his code is doing as well, only much shorter. I'll let it stand because I think it could still be useful for other people.

Konrad Rudolph · Accepted Answer · 2008-12-19 17:48:20Z

3

I've just found a German code snippet on ActiveVB that creates a screenshot form a web site. Perhaps you can build on that? Unfortunately, the code is not only explained in German, but also in VB6. Still, the logic is essentially the same and shouldn't be hard to port to .NET. Hope that helps.

answered Dec 19, 2008 at 17:48

Konrad Rudolph

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Yuliy · Accepted Answer · 2008-12-18 22:23:06Z

2

What are you trying to do?

Are you trying convert a web page to JPEG? This will require a bit more code, as what your code is trying to do is to download an already existing image (such as a gif, png, or even another jpeg) and converts it to jpeg. You would need to have something render the HTML document, then you would need to capture an image of the rendered document, and then save that as a JPEG.

answered Dec 18, 2008 at 22:23

Yuliy

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DKATDT Over a year ago

Thats correct. Any clues as to what I can use to render the document and save it as a jpg?

Yuliy Over a year ago

You might be able to use a Winforms WebBrowser (msdn.microsoft.com/en-us/library/…). I don't know what you would use to then take a screenshot from this.

Zachary Yates · Accepted Answer · 2008-12-18 22:24:39Z

1

It's probably easier to use System.Net.WebClient, I think you can remove all but 2 or 3 lines of code. i.e.: WebClient.DownloadFile()

MSDN page

answered Dec 18, 2008 at 22:24

Zachary Yates

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Joel Coehoorn Over a year ago

That will just get the html text: it still won't get the image, nor any other images, styles, or scripts the page may need to render.

Matt Hamilton · Accepted Answer · 2008-12-18 22:43:18Z

I know you're asking for VB, but here's some C# code that I use in a project of mine to capture local thumbnails from image URLs (asynchronously). I've tried to strip out all the project-specific stuff so it makes sense as a stand-alone example.

var wc = new WebClient();
wc.CachePolicy = new RequestCachePolicy(RequestCacheLevel.NoCacheNoStore);
wc.DownloadDataCompleted += wc_DownloadDataCompleted;

wc.DownloadDataAsync(imageProvider.Image, "yourFilenameHere");

And here's the wc_DownloadDataCompleted event handler:

private void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
    if (e.Error == null && !e.Cancelled)
    {
        var filename = e.UserState.ToString();

        using (var ms = new MemoryStream(e.Result))
        {
            var bi = new BitmapImage();
            bi.BeginInit();
            bi.StreamSource = ms;
            bi.DecodePixelWidth = 80; // _maxThumbnailWidth;
            bi.EndInit();

            var encoder = new JpegBitmapEncoder();
            encoder.Frames.Add(BitmapFrame.Create(bi));
            var filename = Path.Combine(_thumbFolder, filename);
            try
            {
                using (var fs = new FileStream(filename, FileMode.Create))
                {
                    encoder.Save(fs);
                }
            }
            catch { }
        }
    }
}

Edit

I guess I should add that this was in a WPF application - hence the use of "BitmapImage" and "BitmapFrame" to decode the stream. So it may not help you. I'm gonna leave it here anyway.

Nox · Accepted Answer · 2011-09-08 12:17:46Z

0

Or you could just do this:

    Dim webclient As New Net.WebClient

    Dim FileName As String = "C:\Share\local.Gif"
    webclient.DownloadFile(URI, FileName)
    PictureBox1.Image = Image.FromFile(FileName)

answered Sep 8, 2011 at 12:17

Nox

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