2. Using Appropriate Filters

It is an easy task to develop your filters and image pre-process to detect the plate using the image processing toolbox in Matlab. For example, in India, the plates have black characters on white background.

Region of Interest for the above image from which we extract the License number.

Using the above characteristics of the license plate one can easily extract the Region of Interest(ROI) from an Image. I used an algorithm which uses the RGB values of the pixel to detect the ROI.

All the rectangular regions of an image where the colors are predominantly white near the edges and black in the middle. This step will eliminate most of the redundant data, but areas which have similar color with the same aspect ratio of the plate are present. These, when passed through filters which detect the high contrast will work in most of the cases except when the image background contains patterns similar to plates, such as numbers stamped on a vehicle and textured floors.

For more accuracy, a layer of Neural Network trained on similar datasets can be used.