  For more than half a century, the Hough transform is ever-expanding for new
frontiers. Thousands of research papers and numerous applications have evolved
over the decades. Carrying out an all-inclusive survey is hardly possible and
enormously space-demanding. What we care about here is emphasizing some of the
most crucial milestones of the transform. We describe its variations
elaborating on the basic ones such as the line and circle Hough transforms. The
high demand for storage and computation time is clarified with different
solution approaches. Since most uses of the transform take place on binary
images, we have been concerned with the work done directly on gray or color
images. The myriad applications of the standard transform and its variations
have been classified highlighting the up-to-date and the unconventional ones.
Due to its merits such as noise-immunity and expandability, the transform has
an excellent history, and a bright future as well.
