Method and apparatus for performing registration plate detection with aid of edge-based sliding concentric windows

An apparatus for registration plate detection, comprising:

• a processing circuit, arranged to control operations of the apparatus, comprising:
• an image processing module, arranged to process image data of a predetermined region of an input image to generate an edge image, comprising:
• a gradient image creation unit, arranged to perform a gradient calculation upon the image data of the predetermined region to generate a gradient image, wherein the gradient image comprises gradient data of the predetermined region;
• and
• an edge threshold estimation unit, arranged to perform edge threshold estimation upon the gradient data of the predetermined region to update an edge threshold via a set of iterative calculations, wherein the image processing module processes the image data of the predetermined region according to the edge threshold and according to a selective filter, to generate the edge image;
• and
• a registration plate detecting module, arranged to perform registration plate detection according to the image data of the predetermined region and according to the edge image, to determine a location of a registration plate image in the predetermined region, for performing post-processing corresponding to the registration plate image;
• wherein the gradient image comprises a plurality of pixels corresponding to the predetermined region, and the gradient data of the predetermined region are utilized as gray levels of the plurality of pixels of the gradient image;
• a ratio of extreme pixel represents a ratio of a number of a set of extreme pixels having a common extreme gray level in a binarized version of the gradient image to a total number of pixels in the binarized version;
• the set of iterative calculations comprises a first iterative calculation and a second iterative calculation following the first iterative calculation;
• the edge threshold estimation unit performs the first iterative calculation to generate a first candidate value of the edge threshold, and uses an equation involving the ratio of extreme pixel and the first candidate value to calculate a second candidate value of the edge threshold during the second iterative calculation.