Detect custom image marker in real time using OpenCV on iOS

Question

I would like some hints, maybe more, on detecting a custom image marker in a real-time video feed. I'm using OpenCV, iPhone and the camera feed. By custom image marker I'm referring to a predefined image, but it can be any kind of image (not a specific designed marker). For example, it can be a picture of some skyscrapers.

I've already worked with ARTags and understand how they are detected, but how would I detect this custom image and especially find out its position & orientation?

What makes a good custom image to be detected successfully?

Thanks

Answer 1

The most popular markers used in AR are

• AR markers (a simple form of QR codes) - those detected by AR tookit & others
• QR codes. There are plenty of examples on how to create/detect/read QR.
• Dot grids. Similar with the chess grids used in calibration. It seems their detection can be more robust than the classical chess grid. OpenCV has codes related to dot grid detection in the calibration part. Also, the OpenCV codebase offers a good starting point to extract 3D position and orientation.
• Chess grids. Similar to dot grids. They were the standard calibration pattern, and some people used them for marker detection of a long time. But they lost their position to dot grids recently, when some people discovered that dots can be detected with better accuracy.

Note :

Grids are symmetrical. I bet you already know that. But that means you will not be able to recover full orientation data from them. You will get the plane where the grid lies, but nothing more.

Final note :

Code and examples for the first two are easily found on the Internet. They are considered the best by many people. If you decide to use the grid patterns, you have to enjoy some math and image processing work :) And it will take more.

Answer 2

This answer is valid no more since Vuforia is now a paid engine.

I think you should give Vuforia a try. It's a AR engine that can use any image you want as a marker. What makes a good marker for Vuforia is high frequency images.

http://www.qualcomm.com/solutions/augmented-reality

Vuforia is a free to use engine.