public bool IsBiColour(int FileHandle, int PageRef)
{
    double renderScale = base.GetRenderScale();
    SetRenderScale(0.1);

    base.SetGDIPlusOptions(1, 0);       // turn text / vector smoothing off so we get a true bicolour image
    base.SetGDIPlusOptions(3, 0);       // turn image smoothing off (off as default anyway)

    bool biColour = false;

    using (MemoryStream ms = new MemoryStream(base.DARenderPageToString(FileHandle, PageRef, 0, 300)))
    {
        using (Bitmap bitmap = new Bitmap(ms))
        {
            List<int> colours = new List<int>();

            for (int y = 0; y < bitmap.Height && colours.Count <= 2; y++)
            {
                for (int x = 0; x < bitmap.Width && colours.Count <= 2; x++)
                {
                    int colour = bitmap.GetPixel(x, y).ToArgb();
                    if (!colours.Contains(colour)) colours.Add(colour);
                }
            }

            biColour = (colours.Count <= 2);
        }
    }

    SetRenderScale(renderScale);
    return biColour;
}

A (very) minor annoyance is there is no GetGDIPlusOptions. I can set the options but I cannot restore them back to their previous values (like I do with renderScale).

 

Ingo's answer is a good solution.

Another idea is to render the PDF to a low DPI BMP file and then manually counting the colours.

There is no easy solution to this.

Another option is to call QP.GetPageColorSpaces functions to see which colorspaces are directly referenced.  

You will need to do testing with each solution to make sure it is working correctly with your PDF's. The PDF spec is very complex and there are many tricks that can be used including functions and Indexed colorspaces.

It will be interesting to hear about your testing.

Andrew.

there's a lot you can "see" without a pdf-library.

Please read my blog here:

http://pdfcomments.blogspot.de/2009/09/under-surface.html

What you're looking for is code like the following:

// ...

// textcomplete contains the filecontent ...

devrgb  := CountSubStr('/DEVICERGB', UpperCase(textcomplete));

devcmyk := CountSubStr('/DEVICECMYK', UpperCase(textcomplete));

devgray := CountSubStr('/DEVICEGRAY', UpperCase(textcomplete));

// ...

Cheers and welcome here,

Ingo

 

This is my first post so please be gentle . Is there any way to tell if a PDF page is black and white or colour (e.g. 256 colour, 65536 colour, 24bit etc). Reason why I'm asking is I want to decide which format to save an image in before I render it (Black and White G4 TIFF, everything else JPG etc.)