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POWhy is my image distorted when decoding as FlateDecode using iTextSharp?
 

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  1. POWhy is my image distorted when decoding as FlateDecode using iTextSharp?
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    <p>When decoding an image within a PDF as <code>FlateDecode</code> via iTextSharp the image is distorted and I can't seem to figure out why. </p> <p>The recognized bpp is <code>Format1bppIndexed</code>. If I modify the <code>PixelFormat</code> to <code>Format4bppIndexed</code> the image is recognizable to some degree (shrunk, coloring is off but readable) and is duplicated 4 times in a horizontal manner. If I adjust the pixel format to <code>Format8bppIndexed</code> it is also recognizable to some degree and is duplicated 8 times in a horizontal manner. </p> <p>The image below is after a <code>Format1bppIndexed</code> pixel format approach. Unfortunately I am unable to show the others due to security constraints.</p> <p><img src="https://i.stack.imgur.com/xtUss.png" alt="distorted image"></p> <p>The code is seen below which is essentially the single solution I have come across littered around both SO and the web.</p> <pre><code>int xrefIdx = ((PRIndirectReference)obj).Number; PdfObject pdfObj = doc.GetPdfObject(xrefIdx); PdfStream str = (PdfStream)(pdfObj); byte[] bytes = PdfReader.GetStreamBytesRaw((PRStream)str); string filter = ((PdfArray)tg.Get(PdfName.FILTER))[0].ToString(); string width = tg.Get(PdfName.WIDTH).ToString(); string height = tg.Get(PdfName.HEIGHT).ToString(); string bpp = tg.Get(PdfName.BITSPERCOMPONENT).ToString(); if (filter == "/FlateDecode") { bytes = PdfReader.FlateDecode(bytes, true); System.Drawing.Imaging.PixelFormat pixelFormat; switch (int.Parse(bpp)) { case 1: pixelFormat = System.Drawing.Imaging.PixelFormat.Format1bppIndexed; break; case 8: pixelFormat = System.Drawing.Imaging.PixelFormat.Format8bppIndexed; break; case 24: pixelFormat = System.Drawing.Imaging.PixelFormat.Format24bppRgb; break; default: throw new Exception("Unknown pixel format " + bpp); } var bmp = new System.Drawing.Bitmap(Int32.Parse(width), Int32.Parse(height), pixelFormat); System.Drawing.Imaging.BitmapData bmd = bmp.LockBits(new System.Drawing.Rectangle(0, 0, Int32.Parse(width), Int32.Parse(height)), System.Drawing.Imaging.ImageLockMode.WriteOnly, pixelFormat); Marshal.Copy(bytes, 0, bmd.Scan0, bytes.Length); bmp.UnlockBits(bmd); bmp.Save(@"C:\temp\my_flate_picture-" + DateTime.Now.Ticks.ToString() + ".png", ImageFormat.Png); } </code></pre> <p>What do I need to do to so that my image extraction works as desired when dealing with <code>FlateDecode</code>?</p> <p><strong>NOTE</strong>: I do not want to use another library to extract the images. I am looking for a solution leveraging <em>ONLY</em> iTextSharp and the .NET FW. If a solution exists via Java (iText) and is easily portable to .NET FW bits that would suffice as well.</p> <p><strong>UPDATE</strong>: The <code>ImageMask</code> property is set to true, which would imply that there is no color space and is therefore implicitly black and white. With the bpp coming in at 1, the <code>PixelFormat</code> should be <code>Format1bppIndexed</code> which as mentioned earlier, produces the embedded image seen above.</p> <p><strong>UPDATE</strong>: To get the image size I extracted it out using Acrobat X Pro and the image size for this particular example was listed as 2403x3005. When extracting via iTextSharp the size was listed as 2544x3300. I modified the image size within the debugger to mirror 2403x3005 however upon calling <code>Marshal.Copy(bytes, 0, bmd.Scan0, bytes.Length);</code> I get an exception raised.</p> <blockquote> <p>Attempted to read or write protected memory. This is often an indication that other memory is corrupt.</p> </blockquote> <p>My assumption is that this is due to the modification of the size and thus no longer corresponding to the byte data that is being used.</p> <p><strong>UPDATE</strong>: Per Jimmy's recommendation, I verified that calling <code>PdfReader.GetStreamBytes</code> returns a byte[] length equal to width<em>height/8 since <code>GetStreamBytes</code> should be calling <code>FlateDecode</code>. Manually calling <code>FlateDecode</code> and calling <code>PdfReader.GetStreamBytes</code> both produced a byte[] length of 1049401, while the width</em>height/8 is 2544*3300/8 or 1049400, so there is a difference of 1. Not sure if this would be the root cause or not, an off by one; however I am not sure how to resolve if that is indeed the case.</p> <p><strong>UPDATE</strong>: In trying the approach mentioned by kuujinbo I am met with an <code>IndexOutOfRangeException</code> when I attempt to call <code>renderInfo.GetImage();</code> within the <code>RenderImage</code> listener. The fact that the width*height/8 as stated earlier is off by 1 in comparison to the byte[] length when calling <code>FlateDecode</code> makes me think these are all one in the same; however a solution still eludes me.</p> <pre><code> at System.util.zlib.Adler32.adler32(Int64 adler, Byte[] buf, Int32 index, Int32 len) at System.util.zlib.ZStream.read_buf(Byte[] buf, Int32 start, Int32 size) at System.util.zlib.Deflate.fill_window() at System.util.zlib.Deflate.deflate_slow(Int32 flush) at System.util.zlib.Deflate.deflate(ZStream strm, Int32 flush) at System.util.zlib.ZStream.deflate(Int32 flush) at System.util.zlib.ZDeflaterOutputStream.Write(Byte[] b, Int32 off, Int32 len) at iTextSharp.text.pdf.codec.PngWriter.WriteData(Byte[] data, Int32 stride) at iTextSharp.text.pdf.parser.PdfImageObject.DecodeImageBytes() at iTextSharp.text.pdf.parser.PdfImageObject..ctor(PdfDictionary dictionary, Byte[] samples) at iTextSharp.text.pdf.parser.PdfImageObject..ctor(PRStream stream) at iTextSharp.text.pdf.parser.ImageRenderInfo.PrepareImageObject() at iTextSharp.text.pdf.parser.ImageRenderInfo.GetImage() at cyos.infrastructure.Core.MyImageRenderListener.RenderImage(ImageRenderInfo renderInfo) </code></pre> <p><strong>UPDATE</strong>: Trying varying the varying methods listed here in my original solution as well as the solution posed by kuujinbo with a different page in the PDF produces imagery; however the issues always surface when the the filter type is <code>/FlateDecode</code> and no image is produced for that given instance.</p>
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    1. COHow is the image distorted? Can you post a screenshot? It sounds like you've got the stride wrong somewhere or are multiplying things up incorrectly.
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    2. CO@ChrisF Just added an image
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    3. COIs this related to this question? http://stackoverflow.com/questions/757265/how-does-pdfs-bitspercomponent-translate-to-bits-per-pixel-for-images If not I'll try to dig in a little deeper when I get a chance
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      1. POWhy is my image distorted when decoding as FlateDecode using iTextSharp?
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