White Paperof
CIPA DC-x006- 2008
Stereo Still Image Format for Digital Cameras

This translation has been made based on the original white paper. In the event ofany doubts arising as the contents, the original document is to be the final
authority.

Published by:
Camera & Imaging Products Association

1. Introduction⋆ Background of the standardization
Stereo photography, which records stereo-viewable subject image by taking twocomplementary photographs together, leveraging the fact that human vision isgetting a stereoscopic perception by the parallax between the left and right eyes,
was born at the same time of the birth of photographic technology. The enduring
popularity of stereo photography entertainment events indicates a very high level ofuntapped demand for systems that enable stereoscopic viewing of recorded images.
However, apart from several boom cycles, stereo-photography has never reallytaken hold in the general consumer photography market. This has been attributed
to a range of factors, but probably the most important factor is technical difficultyand equipment complexity involved in camera taking, printing and appreciation on
the display, compared to general photographic technology.
Meanwhile the recent advent of certain models of mobile phones and computers
equipped with 3D (i.e. stereoscopic viewable) displays suggests that 3D
representation applicable equipments may well be embraced by consumer markets.
While binocular type 3D photographic images (called stereo images in thisstandard) have been used by certain users, the applications of stereo images seems
to be spreading into diverse range now, because of the combination of recent rapidly
growing popularization of digital still cameras and the advent of various displays
mentioned above.
In order to make stereo images more appealing and accessible, it will benecessary to have the environment for easy and effective creating and viewing
stereo images while also enhancing the viewing experience. In particular, it isimportant to construct the infrastructure for bridging the gap between the creationof stereo images on digital still cameras (which are enjoying spectacular growth atpresent) and the tools used to view them (such as display devices and printing
systems).
However standard stereo image format has not been established. If this situationis allowed, manufacturers would simply develop a number of different own formats.
This would not only hinder the real popularization but also create unnecessary
confusion with existing services such as photography (printing service) and media
service possibly.
Considering the above-mentioned situation, this document that is the stereo still
image format for digital still cameras designed to provide a standardized format forstereo images and also to promote effective utilization of stereo image data, hasbeen established. Specifically, it sets out regulations for the recording of stereo
images into image files together with associated data (Stim tags) used to coordinate
the camera with the viewing device.
⋆ Objectives of this standard
・ The target is a format compatible with the existing popular binocular stereo
image typically captured by a digital still camera fitted with a stereo imaging
optical adaptor, as shown in the Figure on the next page. It could also potentiallyapply to data created in the same format with authoring tools or equivalent.
・ The aim is to create a stereo image format that is independent of the camera
type or model used to record the image.

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・ A framework for ensuring consistent display quality on a variety of different 3-D
display devices will be provided.
・ Attention should be paid to have no impact on the usage of incompatible devices.

Input
Camera withstereo mode

2D camera

AdaptorTwo 2-D cameras

AdaptorCG system+• Add Stim tags
Data formatted into
stereo image format

Stereo image
Authoring tools

Stereo image format• Add Stim tags+
Body image file (DCF
Representative image
extended image file)
file (DCF basic file)
Stereoimage + Stim tags
Representative image
DCF object

SharingMediaInternet

OutputBaseline device

Compatible device• Stim tags not recognized• Representative image
displayed• Stim tags recognized• Stereo image tailored to output device
Image output device

PC

Figure:CameraMobile phone

Printer

Typical stereo image applications,22. Outline
Basic concept of this standard is that an image data themselves are recorded asexisting 2D (plane) image, and at the same time the attached information, which isnecessarily (otherwise useful) to view the image stereoscopically (i.e. to appreciateas a stereoscopic vision), is combined with the image into one file as some tag data.
This enables the viewer to get proper and effective representation quality at theplayback (or appreciation).
As above mentioned existing 2D image, Jpeg compression is adopted, and the mostcommon location in binocular type stereoscopic image known as the side-by-sideformat (which locates each L or R viewpoint image on the left and right) is used.
As tag information, various items are defined for example;• Which the alignment of the left and right images is, parallel or cross• Image cropping area that would be adequate for stereoscopic viewing.
• Information about camera arrangement at taking picture.
This white paper only lists the names of the tags as the simplest introduction.

3. Scope
This standard specifies the formats to be used for images and metadata related tostereo image (Stim tags), in the case of recording stereo images as image files indigital still cameras and similar devices and systems.
* Note that stereo images in this standard are limited to the binocular (i.e. twoviewpoints) type aligned viewpoint images.

34. File structure
4.1. Purpose
A body image file for stereo images in this standard employs a unique file extension ,which may affect compatibility with image viewers that are not compliant with thisstandard. For this reason, the DCF camera file system rule is leveraged in order toprevent confusion and ensure efficient operation with ordinary image capture andviewing devices (such as digital cameras) by users.
Thus, the DCF object consists of the body image file and a representative image filecontaining the corresponding representative image (see below). This structure
supports unified treatment at standard file operations such as copy, move anddelete for the files. The representative image is substituted for viewing on DCF
readers, while Exif tag information in the representative image file can also beaccessed if required.
4.2. Body image file
The body image file is an image file having the unique file extension, defined as a
DCF extended image file. It consists of the DCF object, with the DCF basic file (i.e.,
the representative image file) .
See the next section about the format of the body image file.
4.3. Representative image file
Recording a body image file shall involves recording the representative image (anyone of the L and R viewpoint images, which is used for 2D playback/display)specified by the representative image tag as a DCF basic file, which consists of theDCF object, with the corresponding body image file.
The image size of the representative image may be any (i.e., resizable).

Figure:File structure45. Body image file format
The body image file format for stereo images (Stim) specified in this standard
conforms to the JPEG Baseline DCT format stipulated in ISO/IEC 10918-1. Anapplication marker segment for the Stim tag (APP3) is also inserted.
The APP3 marker segment consists of the APP3 marker, the Stim identifier code,
the Stim header and the Stim tag (APP3 body), as shown in Figure below.

SOI

APP3 marker

JPEG marker segment

APP3 length(Appn, etc)

Stim identifier code

APP3 marker segment

Stim header

JPEG marker segment
Stim tag(DQT, SOF, etc)
Compressed image
data (Alignedviewpoint image)

EOI

Figure:Structure of body image file incorporating Stim tag56. Stereo image
In this standard, a stereo image refers to an aligned viewpoint image representing aside-by-side combination of two viewpoint images (monocular images corresponding
the left-eye and right-eye viewpoints) in the same plane. The viewpoint images arerectangular in shape.
Hｈ1ｈ2

Alignedviewpoint
imageVFirst viewpoint image area

Figure:Second viewpoint image area

Structure of stereo image

In this standard, the term “aligned viewpoint image” is used to denote the overallimage, while “first viewpoint image area” and “second viewpoint image area” denotethe separate image areas. This convention, as illustrated in the diagram above,
helps to delineate the different image areas in the recorded image. The aligned
viewpoint image consists of the first viewpoint image area on the left-hand side
together with the second viewpoint image area on the right-hand side.

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7. Stim tag elements
When stereo image data is recorded, the Stim tags are stored in the prescribedlocations within the recorded data. The following table lists the names of theelements defined as Stim tags. The Support level of each tag such as 'Mandatory' or'Optional' is specified.

Table:Name of Stim tag elements
Tag name

StimVersion
ApplicationData
ImageArrangement
ImageRotation
ScalingFactor
CropSizeX
CropSizeY
CropOffsetX
CropOffsetY
ViewType
RepresentativeImage
ConvergenceBaseImage
AssumedDisplaySize
AssumedViewDistance
RepresentativeDisparityNear
RepresentativeDisparityFar
InitialDisplayEffectConvergenceDistance
CameraArrangementInterval
ShootingCount

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