Former Winthrop professor responsible for drawing lines on computer

By Amanda Phipps

Jack BresenhamIf you have ever drawn a line on a computer, you should thank a former Winthrop computer science professor. 

Jack Bresenham developed a simplified algorithm for drawing a line on a computer.

This algorithm was first implemented as a software in an IBM computer, but later it was commonly used as hardware, he said.

Bresenham also has a second widely used algorithm for drawing circular arcs. Though the original algorithm for this was never patented, Bresenham simplified it and let it run faster.

The improved method allowed for the generation of arcs of any length above zero degree and up to 360 degrees. This bi-directional improvement was patented.

Bresenham said he holds this patent with Grace and Pi, colleagues from  IBM’s Kingston, N.Y., development laboratory. As with all employee patents, the algorithm patent was assigned to IBM under an agreement employees make when they are hired, Bresenham said.  

Bresenham’s line algorithm allowed for a simpler line drawing process than the previous raster display that used multiplication and division, processes that are slow on a computer, he said.

“My algorithms showed how to avoid multiplication or division to accomplish the same line drawing using only addition and subtraction,” he said.

A raster display is a display device in which tiny lights called pixels are arranged like the squares of a chess board. The lights can be told to turn on or off and what color it should glow when on.

Bresenham’s algorithms simplifies this process by turning on those lights closest to the line that could be drawn. The same process applies to drawing circles on computer screens.

These algorithms for line and circle drawing are used widely today because of their simplicity. They are used in laser printers, TV displays, computer screens, cell phones and digital camera picture modification in programs such as Photoshop, Bresenham said.

Patent process

He stressed that the patent process is one that involves many people.

“A group of engineers collectively come up with a new way to achieve something,” Bresenham said. “Everyone is considered an author of the patent invention.” 

Bresenham also said that the patent system is a way of sharing knowledge. 

“The theory is that patents improve society by making useful inventions available to everyone,” he said.

Because the patent process is difficult, “it is important for businesses to have a working portfolio of patents to work more effectively together,” Bresenham said.

Bresenham obtained his Ph. D. at Stanford University under IBM’s Resident Graduate Fellowship program, he said. The few people who were selected for the program were allowed to enroll in any university worldwide. IBM provided the employees involved in this program their regular salary plus the moving cost to relocate and tuition costs, Bresenham said.

Teaching experience

He began teaching computer science at Winthrop in 1987 and taught for 16 years.

“I always thought about teaching after I finished my Ph.D.,” he said. “I looked forward to teaching and enjoyed it.”

Bresenham has collected nine patents over the years and has travelled as a guest lecturer and teacher. He said he met many people and has had different experiences.

“Sciences and computer work can be a cultural experience in itself,” he said. “(You) learn a lot about yourself and see the different ways people solve life’s problems while traveling.” 

Bresenham is enjoying  his retirement. He travels with his wife Nancy, works out with her three times a week and enjoys good eating.

“My favorite activity,” he said, “is enjoying growing a backyard vegetable garden.”