.DJVU

Introduction

DjVu (said “déjà vu”) is a format for scanned documents, developed at AT&T Labs from 1996. It splits each scanned page into layers: a sharp black-and-white mask for the text and line art, and a low-resolution background and foreground for colour and pictures. Each layer is compressed with a method suited to it, so a scanned page is often much smaller than the same page as a JPEG or a PDF of images.

It is used mostly for scanned books and papers in online libraries and archives. The extension is .djvu or .djv.

Structure

A DjVu file uses the IFF chunk layout, big-endian. It starts with the four bytes AT&T, then a FORM chunk whose type is DJVU for a single page or DJVM for a multi-page document. A page holds an INFO chunk with its size and resolution, an Sjbz chunk with the text mask compressed by JB2, BG44 and FG44 chunks with the wavelet-compressed background and foreground, and optionally hidden text from OCR in a TXTz chunk. A multi-page file starts with a DIRM directory of its pages.

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