.MAC

Introduction

MacPaint was the paint program Apple shipped with the first Macintosh in 1984, written by Bill Atkinson. Its documents hold one black and white page of 576 × 720 pixels, the size of a printed page on the ImageWriter at 72 dots per inch.

On the Mac the files have the type code PNTG and need no extension. Copied to other systems they are usually named .mac or .pntg.

Structure

The file has a 512-byte header: a 4-byte version number, then 38 fill patterns of 8 bytes each, then unused space. The picture follows as 720 rows of 72 bytes, one bit per pixel, with 1 meaning black. Each row is compressed on its own with PackBits, the Mac’s run-length scheme.

A file copied off a Mac may have a 128-byte MacBinary header in front, which holds the Mac file name, type and creator. Readers check for it and skip it.

Links