Detect color pages or BW pages in PDF - itext

Question

Is there any way that I can detect color pages in a PDF file?
For example I have a PDF file with 5 pages, and the first and last page are in color. How can I detect the color pages? Can iText do it?
Now my solution is to convert PDF to images and then detect images color or black&white, but it takes too long time to do it, I need a fast way.
Convert pdf to image by Adobe Acrobat Code as fellows
public static void ConvertPDF2Image(string pdfInputPath, string imageOutputPath,
string imageName, int startPageNum, int endPageNum, ImageFormat imageFormat, double resolution)
{
Acrobat.CAcroPDDoc pdfDoc = null;
Acrobat.CAcroPDPage pdfPage = null;
Acrobat.CAcroRect pdfRect = null;
Acrobat.CAcroPoint pdfPoint = null;
// Create the document (Can only create the AcroExch.PDDoc object using late-binding)
// Note using VisualBasic helper functions, have to add reference to DLL
pdfDoc = (Acrobat.CAcroPDDoc)Microsoft.VisualBasic.Interaction.CreateObject("AcroExch.PDDoc", "");
// validate parameter
if (!pdfDoc.Open(pdfInputPath)) { throw new FileNotFoundException(); }
if (!Directory.Exists(imageOutputPath)) { Directory.CreateDirectory(imageOutputPath); }
if (startPageNum <= 0) { startPageNum = 1; }
if (endPageNum > pdfDoc.GetNumPages() || endPageNum <= 0) { endPageNum = pdfDoc.GetNumPages(); }
if (startPageNum > endPageNum) { int tempPageNum = startPageNum; startPageNum = endPageNum; endPageNum = startPageNum; }
if (imageFormat == null) { imageFormat = ImageFormat.Jpeg; }
if (resolution <= 0) { resolution = 1; }
// start to convert each page
for (int i = startPageNum; i <= endPageNum; i++)
{
pdfPage = (Acrobat.CAcroPDPage)pdfDoc.AcquirePage(i - 1);
pdfPoint = (Acrobat.CAcroPoint)pdfPage.GetSize();
pdfRect = (Acrobat.CAcroRect)Microsoft.VisualBasic.Interaction.CreateObject("AcroExch.Rect", "");
int imgWidth = (int)((double)pdfPoint.x * resolution);
int imgHeight = (int)((double)pdfPoint.y * resolution);
pdfRect.Left = 0;
pdfRect.right = (short)imgWidth;
pdfRect.Top = 0;
pdfRect.bottom = (short)imgHeight;
// Render to clipboard, scaled by 100 percent (ie. original size)
// Even though we want a smaller image, better for us to scale in .NET
// than Acrobat as it would greek out small text
pdfPage.CopyToClipboard(pdfRect, 0, 0, (short)(100 * resolution));
IDataObject clipboardData = Clipboard.GetDataObject();
if (clipboardData.GetDataPresent(DataFormats.Bitmap))
{
Bitmap pdfBitmap = (Bitmap)clipboardData.GetData(DataFormats.Bitmap);
pdfBitmap.Save(Path.Combine(imageOutputPath, imageName) + i.ToString() + "." + imageFormat.ToString(), imageFormat);
pdfBitmap.Dispose();
}
}
pdfDoc.Close();
Marshal.ReleaseComObject(pdfPage);
Marshal.ReleaseComObject(pdfRect);
Marshal.ReleaseComObject(pdfDoc);
Marshal.ReleaseComObject(pdfPoint);
}
////detect image Color or black and white as fellows
Bitmap box1 = new Bitmap(PictureBox1.Image);
Color c = new Color()
int rr, gg, bb;
for(int i=0;i<PictureBox1.Width;i++){
for(int j=0;j<PictureBox1.Height;j++){
c= box1.GetPixel(i,j);
rr= c.R; gg=c.g;bb=c.B;
if（c ==Color.Black||c= Color.White）{
MessageBox.Show("black and white dot")
}
else {
if(rr==gg==bb){
MessageBox.Show("Gray dot");
}
else {
MessageBOx.Show("Color dot")；
}
}
}
}