The cause and method of pre-treatment of PCB optics image in the optics image detection were given at firstly; The
method of circle detection based on traditional Hough transform (THT) was analyzed, and it's shortcomings were given;
To overcome these shortcomings, a method which calls piont Hough transform (PHT) to evaluate the parameters of the
circle was adopted, and it's basic principle was analyzed in detail., It has some advantages such as small amount of data,
high precision and fast speed, but it has some shortcomings also. Accordingly, a method for evaluating the parameters of
the circle based on improved PHT (IPHT) was proposed, which features smaller amount of data and faster speed than the
method of the circle detection of the PHT; At last, the result of experiment for the circle detection of PCB optics image
verified the superiority of the method.