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POHow to extract FlateDecoded Images from PDF with PDFSharp
 

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  1. POHow to extract FlateDecoded Images from PDF with PDFSharp
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    <p>how do I extract Images, which are FlateDecoded (such like PNG) out of a PDF-Document with PDFSharp?</p> <p>I found that comment in a Sample of PDFSharp:</p> <pre><code>// TODO: You can put the code here that converts vom PDF internal image format to a // Windows bitmap // and use GDI+ to save it in PNG format. // [...] // Take a look at the file // PdfSharp.Pdf.Advanced/PdfImage.cs to see how we create the PDF image formats. </code></pre> <p>Does anyone have a solution for this problem?</p> <p>Thanks for your replies.</p> <p><strong>EDIT:</strong> Because I'm not able to answer on my own Question within 8 hours, I do it on that way:</p> <p>Thanks for your very fast reply.</p> <p>I added some Code to the Method "ExportAsPngImage", but I didn't get the wanted results. It is just extracting a few more Images (png) and they don't have the right colors and are distorted.</p> <p>Here's my actual Code:</p> <pre><code>PdfSharp.Pdf.Filters.FlateDecode flate = new PdfSharp.Pdf.Filters.FlateDecode(); byte[] decodedBytes = flate.Decode(bytes); System.Drawing.Imaging.PixelFormat pixelFormat; switch (bitsPerComponent) { case 1: pixelFormat = PixelFormat.Format1bppIndexed; break; case 8: pixelFormat = PixelFormat.Format8bppIndexed; break; case 24: pixelFormat = PixelFormat.Format24bppRgb; break; default: throw new Exception("Unknown pixel format " + bitsPerComponent); } Bitmap bmp = new Bitmap(width, height, pixelFormat); var bmpData = bmp.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, pixelFormat); int length = (int)Math.Ceiling(width * bitsPerComponent / 8.0); for (int i = 0; i &lt; height; i++) { int offset = i * length; int scanOffset = i * bmpData.Stride; Marshal.Copy(decodedBytes, offset, new IntPtr(bmpData.Scan0.ToInt32() + scanOffset), length); } bmp.UnlockBits(bmpData); using (FileStream fs = new FileStream(@"C:\Export\PdfSharp\" + String.Format("Image{0}.png", count), FileMode.Create, FileAccess.Write)) { bmp.Save(fs, System.Drawing.Imaging.ImageFormat.Png); } </code></pre> <p>Is that the right way? Or should I choose another way? Thanks a lot!</p>
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    1. COWith respect to 24 bpp: one format is RGB, the other is BGR. So Marshal.Copy won't do, you have to swap the bytes while you copy. Therefore the wrong colors. You don't align the BMP data at DWORD boundaries. That should explain the distortion.
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      1. USBally ole idjit
 

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