Comic books and mangas are usually stored as comic book archives, a type of file for the purpose of sequential viewing of images. This archive file is not a distinct file format but merely a filename extension naming convention. The filename extension indicates the archive type used:

  • .cb7 → 7z
  • .cbr → RAR
  • .cbz → ZIP

I recommend sticking to .cbz for compatibility and speed. All images inside the archive should already be compressed (using Oxipng, for example). Compressed data doesn’t compress well, so it’s unlikely that .cb7 improves much. And an ebook reader may be slower to open such a file or not open it at all.

To write metadata (such as the author or publisher) to a CBZ file, we can use Calibre with the EmbedComicMetadata plugin. After updating the book on Calibre, select it and click the EmbedComicMetadata icon in the toolbar to embed the metadata in the archive file. To verify that everything worked correctly, unzip the CBZ file (using 7-Zip, for example) and check that it contains a ComicInfo.xml file. Here’s an example of such a file:

<?xml version="1.0"?>
<ComicInfo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Title>Scott Pilgrim's Precious Little Life</Title>
  <Series>Scott Pilgrim</Series>
  <Number>1.0</Number>
  <Year>2004</Year>
  <Month>8</Month>
  <Day>15</Day>
  <Writer>Bryan Lee O'Malley</Writer>
  <Publisher>Oni Press</Publisher>
</ComicInfo>

This file spec originated from the ComicRack application, which is not developed anymore. For the longest time there was no standards body responsible for maintaining this spec, but a coalition of players in the comic book space have joined forces to do just that.