I'm not involved with the app, but there's no need for a hidden marker in this case -- the page IS the marker. It is a planar surface with one of a few known black and white images on it. So: Detect features in each blank drawing, store them in a database included in the app, then use the same corner detector and descriptor at runtime and you have a very constrained feature matching problem.

If you're not familiar with feature detection methods, SIFT is a famous one, though there are much faster methods existing today: http://en.wikipedia.org/wiki/Scale-invariant_feature_transfo...

We use Vuforia and Unity. Adrian Clark did his PhD thesis on tracking and we based our app on his ideas and work. We don't use SIFT as it is patented but we have better research in the pipeline.

It appears to only work on certain pre-defined coloring pages.

Naturally. Those 2D print pages must have 3D models in the app (right?). I'm wondering how the app does feature detection from the camera feed.

Our 3D modeller Shun spends about a week per page carefully designing and animating the models. You are correct, they are per page and completely pre-defined. The fun part is colouring in the pages and seeing the results :D

Even me, 28 year old male, can have a lot of fun with this app.

Why don't you guys allow for printing from within the iOS app?

Personally I'd like to do that but we have a lot of limitations with the Unity platform and supporting multiple platforms. Every feature needs to be implemented at least 2 times (iOS, Android) and tested.

Perhaps in the future once we get some money coming into the company. Right now we don't have any more funds left for development.

I'm sure this has already been discussed, and I know this falls under "easier said than done", but you guys should really try to get this on toy aisle shelves. Perhaps in the form of a book? Maybe have a prominent "Try me!" feature on the cover instructing the user to install the free app and point it at the cover to get people pulled in.

Yeah, other companies are working on this too. I think we are in a unique position at this time with what we've developed.

This is a great idea. I could see this becoming a very popular coloring book series. I'd buy it for my kids.

We've been trying to get major publishers interested for over 8 months. Molasses comes to mind.

With the right marketing and execution and a little luck you'll have tons of traction and be in a better position when they come to you to license your tech for their books!

Why would any kid ever want a "plain old" coloring book without the 3D augmented reality?

Very cool—my kids are going to love for sure!