{"id":96465,"date":"2017-06-26T07:00:00","date_gmt":"2017-06-26T21:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/?p=96465"},"modified":"2019-03-13T01:13:19","modified_gmt":"2019-03-13T08:13:19","slug":"20170626-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20170626-00\/?p=96465","title":{"rendered":"Extracting pages from a PDF document and saving them as separate image files, C# edition"},"content":{"rendered":"

Today’s Little Program extracts the pages from a PDF document and saves them as separate image files. Why? Because I needed to do that. <\/p>\n

I’ll start with the PDF Document<\/a> sample program and change it so that instead of displaying pages on the screen, it saves them to disk. <\/p>\n

Take the C# sample and make these changes to Scenario1_Render.xaml.cs<\/code>:<\/p>\n

\nprivate async void ViewPage()\n{\n    rootPage.NotifyUser(\"\", NotifyType.StatusMessage);\n\n    uint pageNumber;\n    if (!uint.TryParse(PageNumberBox.Text, out pageNumber) ||\n        (pageNumber < 1) || (pageNumber > pdfDocument.PageCount))\n    {\n        rootPage.NotifyUser(\"Invalid page number.\", NotifyType.ErrorMessage);\n        return;\n    }\n\n    \/\/ New: Ask the user for the output file.\n    var save = new FileSavePicker();\n    save.FileTypeChoices[\"PNG image\"] = new[] { \".png\" };\n    var outfile = await save.PickSaveFileAsync();\n    if (outfile == null) return;<\/font>\n\n    Output.Source = null;\n    ProgressControl.Visibility = Visibility.Visible;\n\n    \/\/ Convert from 1-based page number to 0-based page index.\n    uint pageIndex = pageNumber - 1;\n\n    using (PdfPage page = pdfDocument.GetPage(pageIndex))\n    using (var transaction = await outfile.OpenTransactedWriteAsync())\n    {\n        await page.RenderToStreamAsync(transaction.Stream);\n    }<\/font>\n    ProgressControl.Visibility = Visibility.Collapsed;\n}\n<\/pre>\n
Actually, I kind of gutted the program and replaced it with my own stuff. The only interesting parts that remain from the original program are the Load­Document<\/code> method (not shown here) which loads the PDF file into the pdfDocument<\/code> variable, and the part that obtains the PdfPage<\/code> from the user-specified page number. <\/p>\n
We ask for the output file, obtain a write stream to that file, and ask the page<\/code> to render into that stream. The default options generate a bitmap in PNG format whose size matches the declared Size<\/code> of the page. <\/p>\n
The PNG format was fine for my purposes, but the size wasn’t. WinRT view pixels are 1\/96 of an inch, so the resulting bitmap was rendered as if printed to a 96 DPI printer. That’s the resolution of a first-generation fax machine, which isn’t all that great. I wanted 192 DPI, so I needed to render the image at double-size. <\/p>\n
\n    using (PdfPage page = pdfDocument.GetPage(pageIndex))\n    using (var transaction = await outfile.OpenTransactedWriteAsync())\n    {\n        var options = new PdfPageRenderOptions();\n        options.DestinationHeight = (uint)(page.Size.Height * 2);\n        options.DestinationWidth = (uint)(page.Size.Width * 2);\n        await page.RenderToStreamAsync(transaction.Stream, options);<\/font>\n    }<\/font>\n<\/pre>\n
(If I had wanted to change the file format, I’d have set the options.Bitmap­Encoder­Id<\/code> to something like Bitmap­Encoder.<\/code>Jpeg­Encoder­Id<\/code>.) <\/p>\n
I didn’t have a large document to convert, so changing the page number and clicking the (now-mislabeled) “View” button a dozen times wasn’t that big of a deal<\/a>. <\/p>\n
For the rest of the week, I’m going to be translating this program into C++\/CX (twice) and JavaScript (twice). <\/p>\n
Twice? <\/p>\n
Yes, twice. You’ll see. <\/p>\n
And then there will be a bonus. <\/p>\n
I can sense your anticipation. <\/p>\n","protected":false},"excerpt":{"rendered":"
A Little Program I needed.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-96465","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
A Little Program I needed.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/96465","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=96465"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/96465\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=96465"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=96465"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=96465"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}