Despite a short lifespan, MacPaint was many people's first GUI-based bitmap editing experience, and as such became the seminal work by which similar efforts were measured. The first real improvement was FullPaint by Ann Arbor Softworks, then SuperPaint (Silicon Beach Software), PixelPaint (Supermac Technology; the first colour-capable paint program) and eventually Adobe Systems introduced Photoshop around the same time Apple debuted the Macintosh IIfx.
At its introduction (and courtesy of the Macintosh's GUI), MacPaint was radically easier to use than any such program before. It literally redefined expectations of what software could and ought to be. By being bundled with MacWrite (Apple's companion word-processing program for the Mac), people quickly saw how the GUI approach to computer use made more sense than existing user interfaces.
Since the original Macintosh had only a black-and-white monitor, MacPaint only edited monochrome bitmaps with a fixed size of 576 x 720 pixels - the size of an A4 sheet of paper at 72 dpi.
Xerox PARC researcher and Apple Fellow Alan Kay made a seminal home videotape showing his five year-old daughter starting a Macintosh 128K computer, inserting a floppy disk containing MacPaint, starting the program, and proceeding to paint with it. MacPaint, in part, represented a paradigm shift where computing had become a useful (and even entertaining) part of ordinary people's lives.
MacPaint 1.0 was written by Bill Atkinson, a member of Apple's Macintosh development team. In 1988, David Ramsey made some improvements resulting in version 2.0. Both versions came in at around 45 kilobytes for the full application!
Somewhat curiously, the original MacPaint in fact broke many of the user interface guidelines then being pushed by Apple as the key to consistency between applications. MacPaint's interface did not consist of separate windows, but used a full screen approach, with fixed tool palettes in a dedicated area on the left and below the editing area. The window title bar shown above the editing area is fake - it cannot be moved. While this approach fit reasonably well with the single-tasking original Mac OS, the later addition of MultiFinder meant that MacPaint 1.0 didn't play well with others. This was one of the main issues addressed by MacPaint 2.0, which adopted "normal" windows and floating tool palettes.
The original MacPaint did not incorporate a zoom function. Instead, a special magnification mode called FatBits was used, which showed each pixel as a clickable rectangle with a white border. Editing in this mode was extremely easy, and set the standard for many future editors.