LinuxWhat is the TN3 file format?
.tn3 is a raster bitmap image file format used by the Atari ST computer. .tn3 files store still monochrome graphics in the Atari ST's high-resolution mode - 640×400 pixels, single bitplane - using run-length encoding (RLE) to compress the raw bitplane data.
.tn3 files are used for storing high-resolution monochrome images. The Atari ST also used a low-resolution colour format (.tn1, 320×200, 16 colours) and a medium-resolution format (.tn2, 640×200, 4 colours); the generic .tny extension covers all three variants. A related high-resolution still-image format from the same era is .pi3 (DEGAS Elite). .tn3 was developed for Atari ST in the late 1980s, through David Mumper's Tiny Stuff and Tiny View utilities, and was used for another decade - common in demoscene releases and floppy-distributed software.
Security & safety
RISK: LOWTN3 is a static image format with no scripting or executable content, so the file itself is harmless. The only practical caution: it is an obscure retro format, and searching the web for a "TN3 viewer" may lead to bundled-adware "universal file viewers" - stick to RECOIL (open source) or XnView MP from the official site.
Format details
in a nutshellPrograms that open TN3 files
Windows2 apps
RECOIL
Open-source Open the .tn3 directly - RECOIL is a dedicated retro-computer image decoder that natively understands Atari ST Tiny formats; export as PNG. 
XnView MP
Freemium Enable Settings -> General -> 'Show all graphic formats', then open the .tn3; use 'Export' / batch convert to PNG or JPG. 
macOS2 apps
XnView MP
Freemium Enable 'Show all graphic formats', then open/convert the .tn3 (the classic XnView is Windows-only; XnView MP is the cross-platform successor). Technical details
deep spec| Image resolution | 640×400 pixels (Atari ST high-resolution monochrome mode) |
| Color depth | 1-bit monochrome (black and white only) |
| Bitplanes | 1 (single bitplane) |
| Compression | Run-length encoding (RLE) applied to the raw bitplane data |
| File structure | Single leading resolution/flag byte followed by RLE-compressed bitplane data stream |
| Leading resolution byte | Value 2 indicates a plain high-resolution still image; the format is identified by file extension combined with this byte |
| File identification | No fixed magic number or ASCII signature; identified by file extension and leading resolution byte value |
| MIME type | application/octet-stream (no format-specific MIME type registered) |
| Byte order | Big-endian (Motorola 68000 architecture of the Atari ST) |
| Origin platform | Atari ST, specifically requiring the ST monochrome high-resolution monitor |
| Developer | David Mumper; part of the Tiny Stuff and Tiny View utility suite |
| Format family | Atari ST 'Tiny' image family: `.tn1` (low-res, 320×200), `.tn2` (medium-res, 640×200), `.tn3` (high-res, 640×400); generic extension `.tny` |
| Related Atari ST formats | `.pi3` (DEGAS Elite high-res), `.neo` (NeoChrome), `.pi1` / `.pi2` (DEGAS low/medium-res) |
| Era of use | Late 1980s through 1990s; common in Atari ST demoscene releases and floppy-distributed software |
| Modern viewer support | RECOIL (Windows, macOS, Linux), XnView MP (Windows, macOS, Linux) |
| Released | Late 1980s / early 1990s (Atari ST era) |
| Specification | www.fileformat.info |
TN3 conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about TN3 files.
