This image coding scheme is supported natively by the PDF (as “CCITTFaxDecode”) and TIFF (as “T6-encoding”) file formats.

Pad bits are used to fill the image data to a byte boundary. The header is followed by the image data, stored in the Group 4 compressed format for black-and-white images defined in ITU-T Recommendation T.6, Facsimile coding schemes and coding control functions for Group 4 facsimile apparatus.

Bytes 19–20: Size of the references list in bytes.

Bytes 16–18: Size of the image data in bytes.

Bytes 4–10: Illustration identifier (the letters and digits usually seen in the lower right corners of the images).

Bytes 0–2: Size of the illustration in bytes, excluding the padding.

IMAGEF.DAT contains a sequence of illustrations, each with a header, image data, references list, and padding. I describe its format here, for readers who may have these DVDs (sometimes available from Yahoo! Auctions sellers in Japan) but find it inconvenient to use the included viewing application, which works only with Microsoft Windows. When Toyota’s Service Parts Engineering Administration Division publishes the EPC on DVD-ROM discs, the illustrations are stored together in a large file called IMAGEF.DAT.

This isn’t a coincidence: the parts drawings are indeed delivered in a fax image format, presumably because it provides acceptable quality and a good compression ratio. Users of Toyota’s Electronic Parts Catalog (EPC) system, and its derivatives, such as, may have noticed the fax-like quality of the illustrations.

Toyota epc parts catalog