PGM to SIX Converter

SIX is a file extension for SIXEL (Six Pixel) graphics data, a bitmap graphics format developed by Digital Equipment Corporation (DEC) in 1983 and introduced with the LA50 dot matrix printer. SIXEL encodes images as a sequence of printable ASCII characters, where each character represents a column of six vertical pixels (a 'sixel') — the character's ASCII value minus 63 provides a 6-bit binary pattern, with each bit controlling one pixel in the vertical column. The encoding is structured as a series of sixel bands (each six pixels tall) across the image width, with control sequences for color selection (up to 256 registers with HLS or RGB specification), repeat counts (run-length encoding for efficiency), carriage return, and newline commands. SIXEL data is transmitted to the output device using DEC's standard escape sequence protocol, embedded within the text stream alongside regular character output. Originally designed for DEC's line of printers and later supported by DEC VT-series terminals (VT240, VT330, VT340), SIXEL has experienced a remarkable revival in modern terminal emulator software. One advantage is terminal-native image display: SIXEL allows images to be rendered directly within a text terminal session without requiring a graphical window system, enabling command-line tools to display graphs, photographs, and previews inline with text output. This capability has driven adoption in modern terminals like mlterm, xterm, WezTerm, and foot. SIX/SIXEL data can be generated by ImageMagick, libsixel, and chafa, and viewed in any SIXEL-capable terminal emulator.