  In the procedure of surface defects detection for large-aperture aspherical
optical elements, it is of vital significance to adjust the optical axis of the
element to be coaxial with the mechanical spin axis accurately. Therefore, a
machine vision method for eccentric error correction is proposed in this paper.
Focusing on the severe defocus blur of reference crosshair image caused by the
imaging characteristic of the aspherical optical element, which may lead to the
failure of correction, an Adaptive Enhancement Algorithm (AEA) is proposed to
strengthen the crosshair image. AEA is consisted of existed Guided Filter Dark
Channel Dehazing Algorithm (GFA) and proposed lightweight Multi-scale Densely
Connected Network (MDC-Net). The enhancement effect of GFA is excellent but
time-consuming, and the enhancement effect of MDC-Net is slightly inferior but
strongly real-time. As AEA will be executed dozens of times during each
correction procedure, its real-time performance is very important. Therefore,
by setting the empirical threshold of definition evaluation function SMD2, GFA
and MDC-Net are respectively applied to highly and slightly blurred crosshair
images so as to ensure the enhancement effect while saving as much time as
possible. AEA has certain robustness in time-consuming performance, which takes
an average time of 0.2721s and 0.0963s to execute GFA and MDC-Net separately on
ten 200pixels 200pixels Region of Interest (ROI) images with different degrees
of blur. And the eccentricity error can be reduced to within 10um by our
method.

Computer Vision and Pattern Recognition;Image and Video Processing