CBZ - Comic Book Archive (ZIP)

A CBZ file is a comic book, graphic novel or manga volume stored as a plain ZIP archive with one image per page. It is not really a new format at all: it is the ZIP format you already know, given a different extension so comic readers can recognise it. The convention grew out of the comic scanning community and spread with early readers such as CDisplay, which simply showed a folder of pictures one after another. The same idea in other archive formats is where CBR (RAR), CB7 (7-Zip) and CBT (tar) come from.

How a CBZ file stores its pages

Inside a CBZ you find image files, normally JPEG, sometimes PNG for line art or WebP in newer archives. There is no page list: readers sort the filenames and show them in that order, which is why pages are named with leading zeros, such as page001.jpg. It also means that any stray file left in the archive can turn up as a page.

The ZIP wrapper compresses losslessly, but it barely shrinks a comic, because JPEG and PNG pages are already compressed; many CBZ files simply store their pages with no further compression. The quality of the book is therefore entirely the quality of the images inside it. A page scanned to JPEG is lossy and loses a little more each time it is re-saved, while a PNG page keeps exactly what was scanned, at a much larger size. Because the container is ordinary ZIP, any unzip tool opens a CBZ, and fixing a wrong page order is a matter of renaming files and zipping them again.

What metadata a CBZ carries

This is where CBZ is thin, and it is worth being clear about why. ZIP was designed to hold files, not to describe a book, so there is no standard place in a CBZ for a title, an author or an issue number. What a report can read from the archive itself is bookkeeping, one row per page: the archived file name including any folder path it was stored under, the compressed and uncompressed size, a CRC-32 checksum used to confirm the page came out intact, and a modification date and time.

The community filled the gap with a small XML file dropped in beside the pages. ComicInfo.xml, introduced by the ComicRack reader and now written by many tools, is the common one. It holds Series, Title, Number, Volume, Count, Year, Month and Day, the credits (Writer, Penciller, Inker, Colorist, Letterer, CoverArtist, Editor), Publisher, Imprint, Genre, LanguageISO, PageCount, AgeRating, BlackAndWhite, Manga, Characters, Teams, Locations, StoryArc, Summary, Web, and the free-text Notes and ScanInformation. A few tools write a rival file, comet.xml, instead. Neither is part of an official standard, so some readers ignore both.

Personal information in a CBZ tends to hide in the pages rather than in the archive. A photograph or a scan carries EXIF data, the block of device information stored inside an image, so a page can name the scanner or camera make and model, the software that saved it, the date it was made and, if a phone took the picture, GPS coordinates. The Notes and ScanInformation fields traditionally name whoever produced the scan. And the stored file paths and per-page timestamps can reveal the folder structure, and sometimes the user account name, of the machine the archive was built on.

When to use CBZ

CBZ is the right container when what you have is pages of artwork that should be shown one at a time in a fixed order. The obvious alternative is PDF, which packs the same pages into a single document that opens on almost anything and can hold a text layer, bookmarks and proper document metadata, so a PDF comic can be searched. A CBZ has no text layer to search. Against CBR the difference is the archive underneath: ZIP is open and built into every operating system, while creating a RAR needs specific software, so a CBZ is easier to make, to repair and to open years later.