Colour Detection on Page

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Hi All, 
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.)

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making Members Profile Find Members Posts Beginner Joined: 09 Jan 14 Location: UK Status: Offline Points: 5	Post Options Post Reply Quote making Report Post Thanks(0) Quote Reply Topic: Colour Detection on Page Posted: 09 Jan 14 at 11:20PM
	Hi All, 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.)

Ingo Members Profile Find Members Posts Moderator Group Joined: 29 Oct 05 Status: Offline Points: 3530	Post Options Post Reply Quote Ingo Report Post Thanks(0) Quote Reply Posted: 12 Jan 14 at 1:41PM
	Hi Making, 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
	Cheers, Ingo

AndrewC Members Profile Find Members Posts Moderator Group Joined: 08 Dec 10 Location: Geelong, Aust Status: Offline Points: 841	Post Options Post Reply Quote AndrewC Report Post Thanks(0) Quote Reply Posted: 14 Jan 14 at 11:13AM
	A complex question. 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.

making Members Profile Find Members Posts Beginner Joined: 09 Jan 14 Location: UK Status: Offline Points: 5	Post Options Post Reply Quote making Report Post Thanks(0) Quote Reply Posted: 14 Jan 14 at 1:26PM
	Thanks Andrew and Ingo, After a lot of playing about it looks like the rendering could be the safest approach. There's lot of colourspaces but we also need to take into account the actual colour of any images being rendered. I came up with the following C# which seems to work most of the time (I've got a class derived from the Quick PDF class, hence the base. calls): 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).