IText. Extracting images. Am I only getting thumbnails?

Question

C++ / C#

Hello.
There is a document with scanned pictures. You need to extract them. Code example:

string src = PDFSourcePath;
            PdfReader reader = null;
            try {
                reader = new PdfReader(src);
                for (int i = 0; i <= reader.NumberOfPages - 1; i++) {
                    try {
                        PdfDictionary page = reader.GetPageN(i);
                        PdfDictionary resources = page.GetAsDict(PdfName.RESOURCES);
                        PdfDictionary xobjects = resources.GetAsDict(PdfName.XOBJECT);
                        int j=0;
                        foreach (PdfName imgRef in xobjects.Keys) {
                            j++;
                            try {
                                PRStream imgStream = (PRStream) xobjects.GetAsStream(imgRef);
                                PdfImageObject imgObject = new PdfImageObject(imgStream);
                                System.Drawing.Image ImgPDF = imgObject.GetDrawingImage();
                                string image_ext = GetImageExtention(ImgPDF);
                                ByteArrayToFile(System.IO.Path.GetDirectoryName(PDFSourcePath) + "\\image"+i+"."+j+".jpg", imgObject.GetImageAsBytes());
                                ImgPDF.Save(System.IO.Path.GetDirectoryName(PDFSourcePath) + "\\image." + i + "." + j + ".png", ImageFormat.Png);
                            }
                            catch (Exception _ex) {

                            }
                        }
                    }catch(Exception _ex01) {

                    }
                }
            }
            catch(Exception _ex) { 
            }
            finally {
                if (reader != null) {
                    reader.Close();
                }
            }

But instead of a normal image, I get only thumnails of images, but with large sizes in bytes. I open it, and there are only squares and pieces of text: No one came across? Is there any way to extract normal quality images? PS When viewing a PDF-reader, I observe how these tumbnails appear for a split second and then are replaced by normal images.