Photoshop CS4, the current eleventh iteration of the program, was officially announced on 23 September 2008 and released on 15 October 2008. "CS" reflects its integration with other Creative Suite products, and the number "4" represents it as the fourth version released since Adobe re-branded its products under the CS umbrella.
In 1987, Thomas Knoll, a PhD student at the University of Michigan, began writing a program on his Macintosh Plus to display grayscale images on a monochrome display. This program, called Display, caught the attention of his brother John Knoll, an Industrial Light & Magic employee, who recommended Thomas turn it into a full-fledged image editing program. Thomas took a six month break from his studies in 1988 to collaborate with his brother on the program, which had been renamed ImagePro.
Later that year, Thomas renamed his program Photoshop and worked out a short-term deal with scanner manufacturer Barneyscan to distribute copies of the program with a slide scanner; a "total of about 200 copies of Photoshop were shipped" this way.
During this time, John traveled to Silicon Valley and gave a demonstration of the program to engineers at Apple Computer Inc. and Russell Brown, art director at Adobe. Both showings were successful, and Adobe decided to purchase the license to distribute in September 1988. While John worked on plug-ins in California, Thomas remained in Ann Arbor writing program code. Photoshop 1.0 was released in 1990 for Macintosh exclusively.