Spiral Architecture (SA) is a relatively new and powerful approach to machine vision system. The geometrical arrangement of pixels on SA can be described as a collection of hexagonal pixels. However, all the existing hardware for capturing image and for displaying image are produced based on rectangular architecture. Therefore, it becomes important to find a proper software approach to mimic SA so that images represented on the traditional square structure can be smoothly converted from or to the images on SA. For accurate image processing, it is critical to best maintain the image resolution during the image conversion. In this paper, we present an algorithm for bilinear interpolation of pixel values on a simulated SA. Our experimental results show that the bilinear interpolation improves the image representation accuracy while keeping the computation simple.