Design rule for Camera File system


Design rule for Camera File system

Design rule for Camera File system (DCF) is a JEITA specification (number CP-3461) which defines a file system for digital cameras, including the directory structure, file naming method, character set, file format, and metadata format. It is currently the de facto industry standard for digital still cameras. The file format of DCF conforms to the Exif specification, but the DCF specification also allows use of any other file formats.

The latest version of the standard is 2.0 (2010 edition).

Contents

Directory and file structure

The filesystem in a digital camera contains a DCIM (Digital Camera IMages) directory which contains possibly multiple subdirectories with names such as "123ABCDE", which consist of a unique directory number (in the range 100…999) and five alphanumeric characters, which may be freely chosen and often refer to a camera maker. These directories contain files with names such as "ABCD1234.JPG", which consist of four alphanumeric characters (often "DSC_" or "IMG_"), followed by a number. The file extension is "JPG" for Exif files and "THM" for Exif files that represent thumbnails of other files than "JPG". Other file formats use different extensions. Multiple files sharing a number (even if the file extension or the four alphanumeric characters are different) are considered related and form a DCF object.

For example, the files on a Nikon D40 are arranged according to the above specification. Thus, a card formatted by the camera will have a partition named "NIKOND40", with a subdirectory named "DCIM". This directory contains a subdirectory named by default "100NCD40", in which images are stored. Images are named "DSC_xxxx", where xxxx represents the file's sequential number.

As this is an industry standard, similar directory structures and naming procedures can be found in most digital cameras.

An example of DCF directory and file structure:

  • Root
    • DCIM (directory)
      • 100ABCDE (a DCF directory)
        • ABCD0001.JPG (a DCF basic file or DCF optional file)
        • ABCD0002.JPG
        • ABCD0003.TIF (a DCF extended image file)
        • ABCD0003.THM (a DCF thumbnail file for extended image file; it is not allowed for ".JPG" files)
        • ABCD0004.WAV (a DCF object need not include an image file)
        • ABCD0005.JPG
        • ABCD0005.WAV (a DCF object formed by naming non-image file with the same file number as an image file)
        • ...
        • ABCD9999.JPG
        • README.TXT (other file names and extensions may be assigned freely)
        • ETC (directories other than DCF directories are also allowed; they shall not have the same name as DCF file)
      • ...
      • 999ABCDE (a DCF directory)
        • ABCD0001.JPG (a DCF basic file or DCF optional file)
        • ... etc.

DCF objects

DCF object is a standalone file with DCF filename (e.g. ABCD0001.JPG) or a file group that share the same file number. DCF objects are used for the files related with each other, such as the image file and the related audio file. Related files are handled together for the convenience of users. A DCF object need not include an image file. A standalone file for which no other file with the same file number exists is still a DCF object. Files in directories that are not located under a DCF directory are not DCF object components.

DCF specification defines files included in DCF objects:

  • DCF basic file - an image file with filename extension ".JPG" conforming to the Exif specification; uses sRGB color space
  • DCF optional file - an image file with filename extension ".JPG" conforming to the Exif specification, used when an image is to undergo extensive processing notably in professional uses; uses DCF optional color space
  • DCF extended image file - a file with other filename extension and data structure than "JPG" or "THM".
  • DCF thumbnail file - a thumbnail image file with filename extension ".THM", used for extended image file; uses sRGB color space and JPEG compression

Files not specified in DCF specification (with other extensions and data structures) may also be included in a DCF object (e.g. "TXT", "WAV", "TIF", etc.).

The rules for DCF object structure and elements prohibit the use of DCF thumbnail files for files with ".JPG" extension. They also prohibit the extension "JPG" for other than DCF basic files and DCF optional files.

One DCF directory may contain up to 9999 DCF objects, numbered from "0001" to "9999" (a.k.a. "File number").

DCF media

DCF media is defined as a removable memory recorded in compliance with the DCF specification or, removable and non-removable memory that a file system can access from an external device through IF (regardless of wired or wireless).

Access

Camera file systems can usually be accessed by directly mounting them via the USB mass storage device class protocol, which exposes the file layout, whether DCF compliant or otherwise. Alternatively, and independent of DCF, files may be accessed via the Picture Transfer Protocol, which provides an object-oriented view and need not expose the file layout.

The file system layout is often opaque to users, as images are copied onto a computer or printer and the application deals with layout.

See also

References

External links



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