Early versions of the AI file format are true EPS files with a restricted, compact syntax, with additional semantics represented by Illustrator-specific DSC comments that conform to DSC's Open Structuring Conventions. These files are identical to their corresponding Illustrator EPS counterparts, but with the EPS procsets (procedure sets) omitted from the file and instead externally referenced using %%Include directives.
The AI file format was originally a native format called PGF. PDF compatibility is achieved by embedding a complete copy of the PGF data within the saved PDF format file. The same “dual path” approach is used when saving EPS-compatible files in recent versions of Illustrator.
Programs that supports AI filesEdit
Aside from Adobe Illustrator, the following applications can edit .ai files:
- CorelDRAW (proprietary program) can natively edit this file format with some limitations.
- Corel Paint Shop Pro (proprietary program) can natively edit this file format.
- FreeHand (proprietary program) can natively open and edit .ai file format version 8 or lower. FreeHand will export to .ai version 7 format.
- Ghostscript (GPL-licensed program) can convert AI postscript files into various formats, and also allows programs that use Ghostscript such as GIMP to import AI files.
- Inkscape (a free, GPL-licensed program) can import the old Postscript-based Adobe Illustrator format (up to AI ver.8) and AI files based on PDF (AI 9.0 and above).
- Skencil (GPL-licensed program) also claims to have some AI support.
- sK1 (a free, GPL-licensed vector graphics editor) supports PostScript-based AI files up to AI ver. 9.
- UniConvertor (a free, GPL-licensed vector graphics translator) supports PostScript-based AI files up to AI ver. 9.
- Xara Xtreme (proprietary program) has support for the format that is described as "working". Xara Xtreme for Linux has similar support.
- XnView, a freeware graphics format converter, claims to be able to read AI file formats, if the AI file was saved with the PDF compatibility option. It does not support all AI subformats.
- FlexiSign (Vector Program used in Signmaking) Can read AI files.
- EnRoute (Vector program for routers) Can read AI files.
- Adobe Reader can open .ai files for viewing if they are saved with the PDF compatibility option
- Adobe Photoshop
- Preview can view .ai files