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I've built an imaging system with a webcam and feature matching such that as I move the camera around; I can track the camera's motion. I am doing something similar to here, except with the webcam frames as the input.

It works really well for "good" images, but when taking images in really low light lots of noise appears (camera high gain), and that messes with the feature detection and matching. Basically, it doesn't detect any good features, and when it does, it cannot match them correctly between frames.

Does anyone know a good solution for this? What other methods are used for finding and matching features?

Here are two example images with very low features:

Frame 1

Frame 2

mevatron
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Jason
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1 Answers1

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I think phase correlation is going to be your best bet here. It is designed to tell you the phase shift (i.e., translation) between two images. It is much more resilient (but not immune) to noise than feature detection because it operates in frequency space; whereas, feature detectors operate spatially. Another benefit is, it is very fast when compared with feature detection methods. I have an implementation available in the OpenCV trunk that is sub-pixel accurate located here.

However, your images are pretty much "featureless" with the exception of the crease in the middle, so even phase correlation may have some trouble with it. Think of it like trying to detect translation in a snow storm. If all you can see is white, you can't tell that you have translated at all, thus the term whiteout. In your case, the algorithm might suffer from "greenout" :)

Can you adjust the camera settings to work better in low-light conditions. Have you fully opened the iris? Can you live with lower framerates? Setting a longer exposure time will allow the camera to gather more light, thus giving you more features at the cost of adding motion blur. Or, if low-light is your default environment you probably want something designed for this like an IR camera, but those can be expensive. Other than that, a big lens and long exposures are your friend :)

Histogram equalization may be of interest in improving the image contrast. But, sometimes it can just enhance the noise. OpenCV has a global histogram equalization function called equalizeHist. For a more localized implementation, you'll want to look at Contrast Limited Adaptive Histogram Equalization or CLAHE for short. Here is a good article on it. This page has some nice examples, and some code.

mevatron
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  • I was actually in the midst of downloading the latest SVN of OpenCV yesterday just for the function you wrote. (Thanks! :) ) Install of openCV was good, but there were a lot of obstacles to getting it to run on a x64 architecture--most of them being with cMake finding and using the correct files. But thanks so much! I'll try this asap. – Jason Feb 24 '12 at 21:58
  • I was wondering if you could help me. I'm working in openCV using your phaseCorrelation code and I'm trying to find a way to get back the matrix C--I want to see what C looks like. I've added this code to your method (_result is function param now): _result.create(C.size(), C.type()); Mat result = _result.getMat(); uchar* data = result.ptr(); for (int i=0;i – Jason Mar 05 '12 at 21:25