1. Field of the Invention
The invention relates to a video image analysis technology, and more particularly, to a license plate recognition system by utilizing spatial-temporal search-space reduction and method thereof.
2. Description of the Related Art
With the accelerated development of economy and technology, vehicles not only play as the means of transportation but also as a sense of identity. However, how to supervise and reduce the vehicles problems effectively, such as traffic accidents and vehicle burglary, are of utmost importance during the past two decades. The present surveillance control of vehicles, such as the high-speed photo detector, or the police patrol, requires a great quantity of manpower. Therefore, using the automatic plate recognition system to cooperate with the above-mentioned work for reducing manpower is coming with the tide of fashion.
However, for the application of plate recognition system, different locations would cause different images. For example, the environment of illumination or plate-like backgrounds, or the plate locations, amounts, sizes, types, colors, even the frames and screws on the plates, would increase the difficulty of plate recognition. Moreover, the conventional plate recognition system can only deal with a plate image once at a time, and is limited by distinguishing the character area from the non-character area in the image. That is, the traditional plate recognition system remains a major challenge in dealing with multiple plate images simultaneously and performing the real-time calculation. Therefore, how to generate the plate recognition system with excellent recognition rate and high-speed calculation is the key issue for vehicle industry.
Therefore, to solve the above-mentioned problems, the present invention proposes a novel license plate recognition system by utilizing spatial-temporal search-space reduction and method thereof to improve the efficiency and performance for recognizing a series of inputted images of license plates.
It is therefore one of the many objectives of the claimed invention to provide a novel license plate recognition method by rapidly searching candidate regions from the inputted image to improve the efficiency of operation.
Another objective of the claimed invention is to provide a license plate recognition method by searching the plate character candidate region based on spatial search-space reduction to avoid redundant calculation of non-plate-character region.
Another objective of the claimed invention is to provide a license plate recognition method by searching the repeated region based on temporal search-space reduction. If the captured scene in the image is still, which means the consecutive images have similar appearances, the candidate regions will have the same or similar classification results. Thus, discarding the repeated candidate regions can avoid redundant calculation and save significantly amount and time of calculation.
Another objective of the claimed invention is to provide a license plate recognition method by utilizing spatial-temporal search-space reduction to improve the efficiency and performance for recognition of real plate character in the consecutive images.
According to the claimed invention, a license plate recognition method by utilizing spatial-temporal search-space reduction is disclosed. The license plate recognition method includes: capturing a plurality of candidate regions from an inputted image, and placing the candidate regions in a candidate area; detecting whether the candidate region of a current image has been appeared on at least a preceding image, if yes, then discarding the candidate region from the candidate area; and outputting the candidate region from the candidate area.
Also according to the claimed invention, a license plate recognition system by utilizing spatial-temporal search-space reduction is disclosed. The license plate recognition system includes: a character edge region detecting module for selecting a plurality of pixels with character edge feature from the inputted image; a plate character candidate region detecting module for selecting a plurality of candidate regions from the image, and if the candidate region comprises at least a plate character, the candidate region is defined as the region that bound the top and bottom of the plate characters tightly; and a repeated region detecting module for detecting if the candidate region of the inputted image has been appeared in a preceding image.
Below, the embodiments of the present invention are described in detail in cooperation with the attached drawings to make easily understood the objectives, technical contents, characteristics and accomplishments of the present invention.
The present invention provides a license plate recognition system by utilizing spatial-temporal search-space reduction and method thereof to improve the efficiency and performance for recognizing a series of inputted images of license plates.
Please refer to
The license plate recognition method in the present invention includes two parts: (1) spatial feature: applying the Bi-level one-pass plate extraction algorithm to extract the candidate region rapidly; and (2) temporal feature: detecting the repeated region and rejecting the candidate region. Please refer to
Step S16 to step S20 show the second part of temporal feature in the present invention: detecting the repeated region and rejecting the candidate region. If the captured scene in the image is still, which means the consecutive images have similar appearances, that is, the candidate regions will have the same or similar classification results. Thus, discarding the repeated regions can avoid redundant calculation and save significantly amount of loading and time. In the present invention, a block match scheme is proposed to calculate the similarity among the inputted images. The similarity can be calculated by the “tangent distance” measure. First, each image is tessellated into blocks with 16×16 dimensions for further comparisons. In step S16, the blocks overlapping with the candidate regions are selected and the system calculates the similarity of blocks in the image at time t−1 and the image at time t. As shown in step S18, the blocks with the distance values lower than a threshold value are regarded as repeated blocks. In step S20, the system discards the overlapped candidate regions, which are overlapped with the repeated regions and the covered area more than a pre-defined percentage. That is, if the pre-defined percentage is 60%, then the system will discard the candidate region with the covered area over 60%.
In
The plate recognition system utilizes the candidate regions in each inputted image to detect the repeated regions. Therefore, when the candidate region is overlapped, the system can use the same block to perform the detecting function without recalculating the similarity of the block. For example, with respect to license plate detecting applications, the related art may need to detect different plates with different sizes, and generate multiple candidate regions in the same image position. In the present invention, the plate recognition system can only calculate the repeated block once to determine a plurality of candidate regions, which dramatically reduces the amount of calculation.
Usually the plate recognition system is required to compute the related features in the image while calculating the similarity of the candidate blocks. For example, the system needs to calculate the tangent vectors of the inputted image while the tangent distance measure is adopted. More tangent vector calculations would cause more loading for the system. Therefore, in the present invention, the plate recognition system adopts one side image feature measure to compute the similarity, such as one side tangent distance measure. That is, in the present invention, the system only extracts the feature from the following block when the system detects the preceding block as a non-repeated block. On the contrary, when the system detects the preceding block as a repeated block, the preceding block and feature can be retained for the following similarity calculation. As shown in
As mentioned above, the license plate recognition method in the present invention first spatially selects the detecting regions, and then compares the regions of different images at different time. Therefore, the system can avoid redundant calculation if there are similar regions, and significantly improves the efficiency and performance for recognizing the images of license plates.
Those described above are only the preferred embodiments to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the shapes, structures, features and spirit disclosed in the specification is to be also included within the scope of the present invention.
Number | Date | Country | Kind |
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97105626 | Feb 2008 | TW | national |