关键词: 车牌定位, 特定颜色对边缘检测, 四元数, 同色调全饱和度

Abstract: License plate location plays an important role in the License Plate Recognition (LPR) system. A license plate location algorithm was presented, which was based on the quaternion specific color-pair edge detection technique. The original color image was first represented by using quaternion Same-Hue-Full-Saturation (SHFS) form. Then, four pairs of masks were used to detect specific color-pair edges. Next, mathematical morphology dilation operation was applied to extract potential license plate regions. Finally, several shape constraint conditions were employed to locate true license plate regions. The proposed method combined the color feature, edge feature and shape feature of license plates, and offered high robustness. The experimental results on 485 car images that are taken under various conditions show that the recall rate is 96.8% and the precision rate is more than 93.2%.

Key words: license plate location, specific color-pair edge detection, quaternion, Same-Hue-Full-Saturation (SHFS)