Removing sun light reflection from images of IR camera in realtime OpenCV application

Question

I am developing speed estimation and vehicle counting application with OpencV and I use IR camera.

I am facing a problem of sun light reflection which causes vertical white region or lines in the images and has bad effect on my vehicle detections.

I want an approach with very high speed, because it is a real-time application.

Answer 1

The vertical streak defect in those images is called "blooming", happens when the one or a few wells in a CCD saturate to the point that they spill charge over neighboring wells in the same column. In addition, you have "regular" saturation with no blooming around the area of the reflection.

If you can, the best solution is to control the exposure (faster shutter time, or close lens iris if you have one). This will reduce but not eliminate blooming occurrence.

Blooming will always occur in a constant direction (vertical or horizontal, depending on your image orientation), and will normally fill entirely one or few contiguous columns. So you can cheaply detect it by heavily subsampling in the opposite dimension and looking for maxima that repeat in the same column. E.g., in you images, you could look for saturated maxima in the same column over 10 rows or so spread over the image height.

Once you detect the blooming columns, you can follow them in a small band around them to try to locate the saturated area. Note that saturation does not necessarily imply values at the end of the dynamic range (e.g. 255 for 8-bit image). Your sensor could be completely saturated at values that the A/D conversion assign at, say, 252. Saturation simply means that the image response becomes constant with respect to the input luminance.

Answer 2

The easiest solution (to me) is a hardware solution. If you can modify the physical camera setup add a polarizing filter to the lens of the camera. You don't even need a(n expensive) camera specific lens, adding a simple sheet of polarized film is good enough Here is one site I just googled "polarizing film" You will have to play with the orientation, but with this mounted position most surfaces are at the same angle and glare will be polarized near horizontal. So you should find a position that works well in most situations.

I've used this method before and the best part is it adds no extra algorithmic complexity or lag. Especially for mounted cameras where all surfaces are at nearly the same angle. This won't help you process the images you currently have but it will help in processing and acquiring future images.