Extracting highlighted content in pdf automatically as images - pdf

Question

I have a pdf file in which some text and images are highlighted using highlight text(U) tool. Is there a way to automatically extract all the highlighted content as separate images and save it to a folder? I dont want readable text. I just want all the highlighted content as images. Thanks

Answer 1

You would need to use PDF library to iterate through all the Annotation objects and their properties to see which ones are using a highlight annotation. Once you have found the highlight annotation you can then extract the position and size (bounding box) of the annotation.
Once you have a list of the annotation bounding boxes you will need to render the PDF file to an image format such as PNG/JPEG/TIFF so that you can extract / clip the rendered image of the annotation text you want. You could use GDI+ or something like LibTIFF
There are various PDF libraries that could do this including
http://www.quickpdflibrary.com (I consult for QuickPDF) or
http://www.itextpdf.com
Here is a C# function based on Quick PDF Library that does what you need.
private void ExtractAnnots_Click(object sender, EventArgs e)
{
int dpi = 300;
Rectangle r;
List<Rectangle> annotList = new List<Rectangle>();
QP.LoadFromFile("samplefile.pdf", "");
for (int p = 1; p <= QP.PageCount(); p++)
{
QP.SelectPage(p); // Select the current page.
QP.SetOrigin(1); // Set origin to top left.
annotList.Clear();
for (int i = 1; i <= QP.AnnotationCount(); i++)
{
if (QP.GetAnnotStrProperty(i, 101) == "Highlight")
{
r = new Rectangle((int)(QP.GetAnnotDblProperty(i, 105) * dpi / 72.0), // x
(int)(QP.GetAnnotDblProperty(i, 106) * dpi / 72.0), // y
(int)(QP.GetAnnotDblProperty(i, 107) * dpi / 72.0), // w
(int)(QP.GetAnnotDblProperty(i, 108) * dpi / 72.0)); // h
annotList.Add(r); // Add the bounding box to the annotation list for this page.
string s = String.Format("page={0}: x={1} y={2} w={3} h={4}\n", p, r.X, r.Y, r.Width, r.Height);
OutputTxt.AppendText(s);
}
}
// Now we have a list of annotations for the current page.
// Delete the annotations from the PDF in memory so we don't render them.
for (int i = QP.AnnotationCount(); i >= 0; i--)
QP.DeleteAnnotation(i);
QP.RenderPageToFile(dpi, p, 0, "page.bmp"); // 300 dpi, 0=bmp
Bitmap bmp = Image.FromFile("page.bmp") as Bitmap;
for (int i=0;i<annotList.Count;i++)
{
Bitmap cropped = bmp.Clone(annotList[i], bmp.PixelFormat);
string filename = String.Format("annot_p{0}_{1}.bmp", p, i+1);
cropped.Save(filename);
}
bmp.Dispose();
}
QP.RemoveDocument(QP.SelectedDocument());
}

Answer 2

Do you want each piece of text as a separate highlight or all the higlhights on a separate pane?