Design rule for Camera File system
Encyclopedia
Design rule for Camera File system (DCF) is a JEITA
Japan Electronics and Information Technology Industries Association
The is a Japanese trade organization for the electronics and IT industries. It was formed in 2000 from two earlier organizations, the Electronic Industries Association of Japan and the Japan Electronic Industries Development Association.-See also:...

 specification (number CP-3461) which defines a file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...

 for digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...

s, including the directory structure, file naming method, character set, file format
File format
A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...

, and metadata format. It is currently the de facto
De facto
De facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...

 industry standard
Standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....

 for digital still cameras. The file format of DCF conforms to the Exif
Exchangeable image file format
Exchangeable image file format is a standard that specifies the formats for images, sound, and ancillary tags used by digital cameras , scanners and other systems handling image and sound files recorded by digital cameras...

 specification, but the DCF specification also allows use of any other file formats.

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

Directory and file structure

The filesystem in a digital camera contains a DCIM (Digital Camera IMages) directory
Directory (file systems)
In computing, a folder, directory, catalog, or drawer, is a virtual container originally derived from an earlier Object-oriented programming concept by the same name within a digital file system, in which groups of computer files and other folders can be kept and organized.A typical file system may...

 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
Nikon D40
The D40 is a now-discontinued Nikon F-mount entry-level digital SLR, announced November 16, 2006. Compared to its predecessor, the D50, the D40 had several features removed, a few added, and a lower price: US$499.95 ESP as of November 2009 with the 18–55 mm G-II kit lens, positioning it as an...

 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
USB mass storage device class
The USB mass storage device class, otherwise known as USB MSC or UMS, is a protocol that allows a Universal Serial Bus device to become accessible to a host computing device, to enable file transfers between the two...

 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
Picture Transfer Protocol
Picture Transfer Protocol is a widely supported protocol developed by the International Imaging Industry Association to allow the transfer of images from digital cameras to computers and other peripheral devices without the need of additional device drivers...

, 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.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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