A comic book archive or comic book reader file (also called sequential image file) is a type of archive file for the purpose of sequential viewing of images, commonly for comic books. The idea was made popular by the CDisplay sequential image viewer; since then, many viewers for different platforms have been created.
Comic book archive files mainly consist of a series of image files, typically PNG (lossless compression) or JPEG (lossy compression) files, stored as a single archive file. Occasionally GIF, BMP, and TIFF files are seen. Folders may be used to group images.
The file name extension indicates the archive type used:
- .cb7 → 7z
- .cba → ACE
- .cbr → RAR
- .cbt → TAR
- .cbz → ZIP
Comic book archive files are not a distinct file format; only the file name extension differs from a standard file of the given archive type.
The file names inside an archive are usually numbered in ascending order according to the original page number, including the use of preceding zeros for all positions (example: using 001 rather than 1) to force the proper display of images by viewers across all operating systems. Otherwise files can be displayed out of order (example: 1, 10-19, 100-199, 2, 20-29, 3, etc.) due to differences in how file name characters are handled by each operating system.
Comic book archive viewers typically offer various dedicated functions to read the content, like one page forward/backwards, go to first/last page, zoom or print. Some applications support additional tag information in the form of embedded XML files in the archive or use of the ZIP comment to store additional information. These files can include additional information like artists, story information, table of contents or even a separate text layer for comic book translations. Efforts, such as the Comic Metadata (CoMet) Format, have been made to define an open standard.