How to find Blank Page in pdf file

I can not detect blank page in pdf file. I have searched internet for it but could not find a good solution.

Using Itextsharp I tried with page size, Xobjects. But they do not give exact result.

I tried

if(xobjects==null || textcontent==null || size <20 bytes )
  then "blank"
else
 not blank

But maximum time it returns wrong answer. I have used Itextsharp

The code is below... I am using Itextsharp Librabry

For xobjects

PdfDictionary xobjects = resourceDic.GetAsDict(PdfName.XOBJECT);
//here resourceDic is PdfDictionary type
//I know that if Xobjects is null then page is blank. But sometimes blank page gives xobjects which is not null.

For contentstream

 RandomAccessFileOrArray f = reader.SafeFile;
 //here reader = new PdfReader(filename);

 byte[] contentBytes = reader.GetPageContent(pageNum, f);
 //I have measured the size of contentbytes but sometimes it gives more than 20 bytes for   blank page

For textcontent

String extractedText = PdfTextExtractor.GetTextFromPage(reader, pageNum, new LocationTextExtractionStrategy());
  // sometimes blank page give a text more than 20 char length .