How to remove one indirectly referenced image from a PDF and keep all others?

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I found a bit of code over at http://ift.tt/1vG5FOz that I have copied here that is an example of how to remove all images (well really all objects). The author admits it is a hack, but it worked for his purposes. The code looks like this:

// Open the PDF
PdfDocument doc = 
    PdfReader.Open("inputfile.pdf", PdfDocumentOpenMode.Modify);

// Loop through every page
foreach (PdfPage page in doc.Pages)
{
    // Get all the resources for every page
    PdfDictionary resource = page.Elements.GetDictionary("/Resources");
    if (resource != null)
    {
        // Get all the external objects
        PdfDictionary objects = resource.Elements.GetDictionary("/XObject");
        if (objects != null)
        {
            // Loop through every item in the external objects
            ICollection items = objects.Elements.Values;
            foreach (PdfItem item in items)
            {
                // Get the reference
                PdfReference reference = item as PdfReference;
                if (reference != null)
                {
                    // Get the underlying values as Pdf Object
                    PdfDictionary xObject = reference.Value as PdfDictionary;
                    // Overwrite the data of the object with 1 byte
                    xObject.Stream.Value = new byte[0];
                }
            }
        }
    }
}

// Save the Pdf as another file
doc.Save("outputfile.pdf");

I modified it to attempt to only delete one object:

// Get all the resources for every page
PdfDictionary resource = pageToImport.Elements.GetDictionary("/Resources");if (resource != null)
{
    // Get all the external objects
    PdfDictionary objects = resource.Elements.GetDictionary("/XObject");
    if (objects != null)
    {
        logInfo.AppendLine(
            string.Format("found {0} XObjects in doc {1}, page {2}",
            objects.Elements.Values.Count, docNum, i + 1));
        // Loop through every item in the external objects
        ICollection<PdfItem> pdfitems = objects.Elements.Values;
        foreach (PdfItem pdfitem in pdfitems)
        {
            // Get the reference
            PdfReference reference = pdfitem as PdfReference;
            if (reference != null)
            {
                // Get the underlying values as Pdf Object
                PdfDictionary xObject = reference.Value as PdfDictionary;

                if (xObject.Elements["/Subtype"].ToString() == "/Image")
                {
                    logInfo.AppendLine(
                    string.Format("Found image XObject with W: {0} H: {1} Len: {2}",
                        xObject.Elements["Width"], xObject.Elements["Height"],
                        xObject.Stream.Length));

                    var hexString = new StringBuilder(400);
                    for (int j = 0; j < Math.Min(200, xObject.Stream.Value.Length); ++j)
                    {
                        hexString.AppendFormat("{0:x2}", xObject.Stream.Value[j]);
                    }

                    logInfo.AppendLine("Image Data:" + hexString.ToString());

                    if (hexString.ToString() == myHexImageData
                    &&  (xObject.Stream.Value.Length == 190656))
                    {
                        // Overwrite the data of the object with empty array
                        xObject.Stream.Value = new byte[0];
                    }
                }
            }
        }
    }
}

This did not work, but instead still deleted all references to the image objects so that none showed up. I am assuming that this essentially is corrupting the file even though the reader still can bring it up.

After searching extensively, I have not found a solution that parses a PDF, finds an image and removes it from the PDF both the references and the XObject.

Is there a way to find all references to an image? If so, how do you remove it, and then remove the image object and keep the integrity of the PDF?

Thanks!

asked 21 secs ago

Robb Sadler

133

How to remove one indirectly referenced image from a PDF and keep all others?