Get DPI definition of image extracted from PDF

I'm using itextSharp to extract images from PDF files.

I used this code as the basis: link

Here is my modified version to support files in memory instead of having to work with files on disk:

    /// <summary>Helper class to extract images from a PDF file. Works with the most
    /// common image types embedded in PDF files, as far as I can tell.</summary>
    /// <example>
    /// Usage example:
    /// <code>
    /// foreach (var filename in Directory.GetFiles(searchPath, "*.pdf", SearchOption.TopDirectoryOnly))
    /// {
    ///    var images = ImageExtractor.ExtractImages(filename);
    ///    var directory = Path.GetDirectoryName(filename);
    ///
    ///    foreach (var image in images)
    ///    {
    ///       image.Save(Path.Combine(directory, name));
    ///    }
    ///  }
    /// </code></example>
    public static class PdfImageExtractor
    {
        #region Methods
        #region Public Methods

        /// <summary>Checks whether a specified page of a PDF file contains images.</summary>
        /// <returns>True if the page contains at least one image; false otherwise.</returns>
        public static bool PageContainsImages(byte[] pdfFile, int pageNumber)
        {
            using (var reader = new PdfReader(pdfFile))
            {
                var parser = new PdfReaderContentParser(reader);
                ImageRenderListener listener = null;
                parser.ProcessContent(pageNumber, (listener = new ImageRenderListener()));
                return listener.Images.Count > 0;
            }
        }

        /// <summary>Extracts all images (of types that iTextSharp knows how to decode) from a PDF file.</summary>
        public static List<System.Drawing.Image> ExtractImages(byte[] pdfFile)
        {
            var images = new List<System.Drawing.Image>();

            using (var reader = new PdfReader(pdfFile))
            {
                var parser = new PdfReaderContentParser(reader);
                ImageRenderListener listener = null;
                for (var i = 1; i <= reader.NumberOfPages; i++)
                {
                    parser.ProcessContent(i, (listener = new ImageRenderListener()));
                    var index = 1;
                    if (listener.Images.Count > 0)
                    {
                        Console.WriteLine("Found {0} images on page {1}.", listener.Images.Count, i);
                        foreach (var pair in listener.Images)
                        {
                            images.Add(pair);
                            index++;
                        }
                    }
                }
                return images;
            }
        }

        /// <summary>Extracts all images (of types that iTextSharp knows how to decode)
        /// from a specified page of a PDF file.</summary>
        /// <returns>Returns a generic <see cref="List&lt;System.Drawing.Image&gt;"/>,
        /// where the key is a suggested file name, in the format: PDF filename without extension,
        /// page number and image index in the page.</returns>
        public static List<System.Drawing.Image> ExtractImages(byte[] pdfFile, int pageNumber)
        {
            var images = new List<System.Drawing.Image>();
            using (var reader = new PdfReader(pdfFile))
            {
                var parser = new PdfReaderContentParser(reader);
                ImageRenderListener listener = null;

                parser.ProcessContent(pageNumber, (listener = new ImageRenderListener()));
                int index = 1;
                if (listener.Images.Count > 0)
                {
                    Console.WriteLine("Found {0} images on page {1}.", listener.Images.Count, pageNumber);
                    foreach (System.Drawing.Image image in listener.Images)
                    {
                        images.Add(image);
                        index++;
                    }
                }

            }


            return images;
        }
        #endregion Public Methods
        #endregion Methods
    }
    internal class ImageRenderListener : IRenderListener
    {
        #region Fields
        List<System.Drawing.Image> images = new List<System.Drawing.Image>();
        #endregion Fields

        #region Properties
        public List<System.Drawing.Image> Images
        {
            get { return images; }
        }
        #endregion Properties

        #region Methods

        #region Public Methods
        public void BeginTextBlock() { }
        public void EndTextBlock() { }
        public void RenderImage(ImageRenderInfo renderInfo)
        {
            PdfImageObject image = renderInfo.GetImage();

            var imageBytes = image.GetImageAsBytes();
            var bytesType = image.GetImageBytesType();

            var fileExtension = bytesType.FileExtension;

            using (var memoryStream = new MemoryStream(imageBytes))
            {
                var drawingImage = System.Drawing.Image.FromStream(memoryStream);

                var dpiX = drawingImage.HorizontalResolution;

                this.Images.Add(drawingImage);
            }
        }
        public void RenderText(TextRenderInfo renderInfo) { }
        #endregion Public Methods
        #endregion Methods
    }

The problem is that in the RenderImage method the value of the dpiX variable is always 96 . I would like to get the original DPI image resolution , is there any way to do this?

To use the method suffice:

var pageImages = PdfImageExtractor.ExtractImages(fileBytes, pageNumber);

For each image, I tried to convert to Bitmap too, but I got the same result:

var bitmapImage = new Bitmap(pageImage);
var dpiX = bitmapImage.HorizontalResolution;
var dpiY = bitmapImage.VerticalResolution;

  

I do not want to set a resolution on my own, I'd like to   get the original resolution of the image.