This article discusses how to improve image processing for autonomous far-field laser beam alignment for the main amplifier in a sizable laser facility. The image process mainly includes two parts, far-field reference computation and far-field center computation. To further enhance the computation stability and the computation efficacy for image processing, the image regions chosen in far-field reference computation and the far-field center computation are all constrained to a particular region. In far-field reference computation, two process flows are shown for the transport spatial filter (TSF) image and cavity spatial filter (CSF) image respectively. In far-field center computation, one process flow is compatible for both the TSF image and CSF image, and the clustering approach is adopted in computing the center of the far-fields. Experimental results demonstrate the effectiveness of the proposed image processing method.