CB7 Comic Book Archive MIME Type

What does application/x-cb7 mean?

The application/x-cb7 media type identifies a CB7 comic book archive. A CB7 is a 7z archive whose members are meant to be read as an ordered sequence of comic pages, usually image files. The conventional extension is .cb7.

CB7 is a usage convention layered on the 7z container, not a separate compression format. The freedesktop.org shared MIME database defines application/x-cb7 as a comic book archive, associates it with .cb7, and treats it as a subtype of application/x-7z-compressed.¹

How can you identify a CB7 file?

Use several clues together:

• The filename ends in .cb7.
• The data is a valid 7z archive.
• Its members are images that form a sensible page sequence.

The first six bytes of a normal 7z archive are 37 7A BC AF 27 1C.³ That signature identifies the container, not the comic-book intent. A general .7z archive and a CB7 can begin with exactly the same bytes, so a decoder must inspect the filename and members as well.

Predictable page names matter because CB7 has no published normative specification for ordering. Names such as 001.jpg, 002.jpg, and 003.jpg sort more consistently than 1.jpg, 2.jpg, and 10.jpg.

Some comic archives also contain ComicInfo.xml. This optional community metadata file can describe the series, issue, creators, publisher, language, page count, page roles, and reading direction.⁴ Its presence is useful but does not make an arbitrary 7z archive a valid CB7 by itself.

Registration and format history

CB7 has no IANA registration, published standard, or authoritative history that establishes one inventor or introduction date.² It belongs to a family of filename conventions in which the last letter points to the archive container: CBZ uses ZIP, CBR uses RAR, CBT uses TAR, and CB7 uses 7z.

The freedesktop.org shared MIME database documents the practical desktop convention and associates .cb7 with application/x-cb7.¹ Application support followed independently. Okular 1.9 added CB7 support in December 2019, and current calibre documentation continues to list CB7 as a supported input format.⁵⁶

The absence of a formal standard leaves details to readers. Software can differ on supported image formats, filename sorting, nested directories, cover selection, metadata, and handling of encrypted archives.

How to open a .cb7 file

Use a comic reader or ebook application with explicit CB7 support. calibre can import and convert CB7, while Okular can present it through its comic-book backend.⁵⁶ Ordinary browsers do not provide a native CB7 reading mode.

A 7z utility can inspect or extract a trusted CB7 because the underlying container is 7z. Extraction gives you the original page files and metadata, but not comic-reader conveniences such as spreads, right-to-left navigation, zoom behavior, or saved reading position.

Support in Poly

Poly recognizes both application/x-cb7 and .cb7 filenames. It classifies CB7 as a document, passes the original file to calibre's ebook-convert, and stores the result as a PDF representation. Poly's PDF pipeline then renders pages, extracts available text, applies OCR when needed, and creates page-level embeddings.

After a successful conversion, Poly provides:

• A thumbnail and paginated preview in the PDF viewer.
• Search over extracted or OCR-recognized page text.
• Visual similarity search at the converted-page level.
• Page text and images that the Poly agent can read together.

This is a converted view, not a native CB7 reader. Poly does not expose the 7z directory, original page images, or ComicInfo.xml as separate searchable records. Page order and appearance depend on calibre's interpretation. Password-protected, damaged, or otherwise unsupported archives can fail conversion.

CB7 compared with CBZ, CBR, and 7z

These formats can hold similar page images, but their containers and media types differ:

7z supports multiple compression methods, solid compression, compressed headers, Unicode filenames, and AES-256 encryption.⁷ Those features can make CB7 compact, but they also mean that a reader needs a capable 7z decoder. ZIP tooling and CBZ support are often easier to find across devices.

Changing .cb7 to .cbz does not convert the archive. Extract the members, preserve their intended order, and create a new ZIP archive when a device requires CBZ.

Converting a CB7

Choose the output around what you need next:

• CBZ for a comic archive based on widely available ZIP tooling.
• PDF for fixed pages, printing, and broad document compatibility.
• EPUB when a reading system requires an ebook package. Image-only pages do not become reflowable text automatically.
• A directory of images for editing, restoration, or separate OCR.

calibre documents CB7 as an input format and chooses the output from the destination extension.⁵

ebook-convert comic.cb7 comic.pdf
ebook-convert comic.cb7 comic.epub

Check page order, spreads, orientation, crop, color, and metadata after conversion. calibre's comic input options can sort pages, trim borders, split landscape images, convert color, and rescale images, so conversion settings can change the result.⁸

Security and privacy

A CB7 can exercise both an archive decoder and every image decoder used on its members. Treat unfamiliar files as untrusted. A MIME label is only a classification hint, and the shared MIME-info specification explicitly warns applications not to trust a file simply because its detected type appears harmless.⁹

7z can encrypt file data and archive headers with AES-256.⁷ Encryption hides content from casual inspection, but it does not authenticate the person who created the archive or make the contents safe. Do not upload a confidential CB7 and its password to an unknown online converter.

ComicInfo.xml may reveal summaries, creator information, publication details, web links, language, and reading preferences beyond what is visible on the pages.⁴ Review it before sharing a privately cataloged archive.

Is a CB7 just a renamed 7z archive?

Structurally, CB7 uses the 7z container. Semantically, the .cb7 extension and application/x-cb7 label tell compatible software to present its image members as an ordered comic. Renaming a 7z archive that already contains sensibly named page images may make it usable in a comic reader. Renaming an unrelated archive does not turn its contents into a comic.