Abstract
This study demonstrates the subpixel interpolation methods to improve the practicable of direct comparison. Three subpixel interpolation methods, fourier transform, linear interpolation method and cubic interpolation method, are applied in this paper. The indices that can evaluate these three methods are concluded as the calculation time, the mean of error sum and the root mean square of error square sum of these three interpolation methods. According to the calculation time, the fastest one is the linear interpolation; instead, the fourier transform is the slowest one. Based on the mean of error sum and the root mean square of error square sum, the differences of these three interpolation methods are very small. Moreover, in the system test, PCBs that include no defects, bridge, missing of small component and missing of large component are tested. After test, in addition to the differences of defects, there are other differences like the print lines on the PCBs and the reflection of light. The position of defects can be marked after using appropriate mask and threshold under the high resolution (324 pixels/mm2).