ISO 12234-2:2001

INTERNATIONAL ISO
STANDARD 12234-2
First edition
2001-10-15
Electronic still-picture imaging —
Removable memory —
Part 2:
TIFF/EP image data format
Imagerie de prises de vue électroniques — Mémoire mobile —
Partie 2: Format de données image TIFF/EP
Reference number
ISO 12234-2:2001(E)
©
ISO 2001

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ISO 12234-2:2001(E)
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ISO 12234-2:2001(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Image data features .2
4.1 TIFF/EP file encoding structure.2
4.2 Image data .5
4.3 Thumbnail images .6
4.4 Burst sequences using chaining .8
4.5 Camera colour space information.9
4.6 Image data compression.9
4.7 Camera information.11
4.8 Picture annotation .11
4.9 Camera and lens settings .11
4.10 Camera characterization .12
5 TIFF/EP tag definitions.13
5.1 TIFF/EP tag list.13
5.2 TIFF/EP tag definitions grouped by function.16
Annex A (informative) Examples of TIFF/EP files .51
A.1 General.51
A.2 Uncompressed RGB.51
A.3 JPEG compressed .55
Bibliography.59
Alphabetical index of TIFF/EP tag definitions .60
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ISO 12234-2:2001(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 12234 may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 12234-2 was prepared by Technical Committee ISO/TC 42, Photography.
ISO 12234 consists of the following parts, under the general title Electronic still-picture imaging — Removable
memory :
� Part 1: Basic removable-memory module
� Part 2: TIFF/EP image data format
� Part 3: Design rule for camera file system (DCF)
Annex A of this part of ISO 12234 is for information only.
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ISO 12234-2:2001(E)
Introduction
The term TIFF/EP refers to Tag Image File Format/Electronic Photography, defined in this part of ISO 12234. The
term “TIFF 6.0” refers to the TIFF Revision 6.0 specification. TIFF/EP is defined to be as compatible as possible
with existing desktop software packages, to enable them to operate with images from electronic still-picture
cameras. TIFF Revision 6.0 is used as the basis for achieving this interoperability with the large installed base of
imaging software. Wherever possible, TIFF/EP uses tags already defined in TIFF 6.0 and provides guidelines for
the use of these tags as well as the allowed field values. New tags are defined to encode image data features that
are not included in TIFF 6.0. These new tags conform to the practices specified in TIFF 6.0. This document also
describes how related images, such as both “parent” high resolution and “thumbnail” low resolution images of the
same subject, or temporal sequence “bursts” of the same scene, can be stored in a single TIFF/EP file.
With the permission of Adobe Systems Incorporated, sections of this TIFF/EP specification have been copied
verbatim from the TIFF 6.0 specification dated June 3, 1992 specification � 1986-1988, 1992 Adobe Systems
Incorporated. All Rights Reserved.
In this part of ISO 12234, references to tags and tag values defined in TIFF 6.0 are shown in bold typeface. Tags
and tag values that are not defined in TIFF 6.0 are identified in italic type face. These new tags have been chosen
to be as compatible as possible with the Exif tags defined in “Digital Still Camera Image File Format Standard
(Exchangeable image file format for Digital Still Cameras: Exif)”, Version 2.1, June 1998 by the Japan Electronic
Industry Development Association (JEIDA). The new TIFF/EP tag-fields containing enumerated values follow the
TIFF 6.0 convention, where the lower half of the values (0 to 127 for byte values, 0 to 32,767 for short values, and
0 to 2,147,483,647 for long values) are reserved by TIFF/EP and the upper half of the values (128 to 255 for byte
values, 32,768 to 65,535 for short values, and 2,147,483,648 to 4,294,967,296 for long values) are private values
that may be registered by I3A.
I3A may be contacted at the Photographic and Imaging Manufacturers Association, 550 Mamaroneck Avenue,
Suite 307, Harrison, NY 10528-1612 USA, or by e-mail at pima@pima.net.
TIFF/EP complies with the TIFF 6.0 specification and uses the same header specified in TIFF 6.0. The reason for
this is to maintain the highest degree of compatibility with existing TIFF readers and to make the adoption of
TIFF/EP, including the new TIFF/EP tags, as easy as possible. In the future, if TIFF is revised, a revised version of
TIFF/EP may be developed using the revised TIFF specification. TIFF/EP editors of a given TIFF/EP version
number shall not update TIFF/EP files having a higher version number without warning the user that, in doing so,
unknown tags will be deleted. This is explained in the section describing the TIFF/EPStandardID tag.
TIFF/EP tag definitions do not allow default values. All values shall be explicitly stated in order to improve
interoperability with future versions of TIFF/EP. Images may be stored in uncompressed form or using JPEG
baseline (DCT based) compression. In the latter case, an uncompressed baseline-TIFF-readable reduced
resolution “thumbnail” image should also be stored in the 0th IFD to allow the images to be identified using a
baseline TIFF 6.0 reader.
TIFF/EP uses the TIFF/JPEG specification given in “DRAFT TIFF Technical Note No. 2”. This method differs from
the JPEG method described in the TIFF 6.0 specification. In the method used within TIFF/EP, each image segment
(tile or strip) contains a complete JPEG data stream that is valid according to the ISO JPEG standard
(ISO/IEC 10918-1). TIFF/EP requires that readers only support the DCT based lossy JPEG process.
TIFF/EP currently does not define how to embed audio information within a TIFF/EP image file. Audio can be
stored in a separate file on the same removable media, if desired, or stored within a TIFF/EP file using a private
TIFF tag obtained from Adobe Corp. This does not preclude a future release of TIFF/EP from implementing
embedded audio as part of the TIFF/EP file.
TIFF/EP image files should be stored in a READ-ONLY fashion using the appropriate file system mechanism. This
will prevent accidental loss of important TIFF/EP tag-value information if the image is edited by a non-TIFF/EP
compliant application. TIFF editors generally remove unknown tags when saving or updating an image file to
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ISO 12234-2:2001(E)
maintain the integrity of the TIFF file, since the unknown tags might not apply to the edited image. By creating
TIFF/EP image files READ-ONLY, accidental loss of important information is prevented. TIFF/EP editors, on the
other hand, shall warn the user, whenever editing a newer version TIFF/EP file with an older version TIFF/EP
editor, that proceeding may result in the loss of information. The mandatory TIFF/EPStandardID tag-field specifies
theTIFF/EP version used increatingaTIFF/EP imagefile.
The International Organization for Standardization (ISO) draws attention to the fact that it is claimed that
compliance with this International Standard may involve the use of patents from the following companies:
� Canon Incorporated
� Eastman Kodak Company
� Fuji Photo Film Company Ltd.
� Nikon Corporation
� Olympus Optical Company Ltd.
The holders of these patent rights have assured ISO that they are willing to negotiate licenses under reasonable
and non-discriminatory terms and conditions throughout the world. In this respect, the statement of the holder of
this patent right is registered with ISO. Information may be obtained from the companies listed. Other companies
have also determined that, upon approval of this International Standard, they too will grant patent licenses in
accordance with ISO Directives, Part 2. Information regarding these companies may also be obtained from the ISO
Central Secretariat
ISO takes no position concerning the evidence, validity and scope of any of the patent rights listed.
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INTERNATIONAL STANDARD ISO 12234-2:2001(E)
Electronic still-picture imaging — Removable memory —
Part 2:
TIFF/EP image data format
1 Scope
This part of ISO 12234 specifies the TIFF/EP data format described in ISO 12234-1.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 12234. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 12234 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 12232:1998, Photography — Electronic still-picture cameras — Determination of ISO speed
ISO 12233:2000, Photography — Electronic still-picture cameras — Resolution measurements
ISO 12234-1:2001, Electronic still-picture imaging — Removable memory — Part 1: Basic removable-memory
module
ISO 14524:1999, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
ISO/IEC 10918-1:1994, Information technology — Digital compression and coding of continuous-tone still images:
Requirements and guidelines
ITU-R BT.709-4 (03/00), Parameter values for the HDTV standards for production and international programme
exchange
3 Terms and definitions
For the purposes of this part of ISO 12234, the following terms and definitions apply.
3.1
file system
software structure which specifies how the data is logically organized on a given storage medium
3.2
image data format
structure and content which specifies how the data is logically organized on a given storage medium
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ISO 12234-2:2001(E)
4 Image data features
This clause describes all the features of the TIFF/EP standard and lists the tags used to implement each feature.
4.1 TIFF/EP file encoding structure
A TIFF/EP file is a valid TIFF file that contains the TIFF/EP format identifier and conforms to the restrictions
described in this part of ISO 12234. The TIFF/EP header is exactly the same as the TIFF header. The use of the
TIFF/EP format and revision number is identified in the TIFF/EPStandardID tag-field.
TIFF is an image file format. In this part of ISO 12234, a file is a sequence of 8-bit bytes, where the bytes are
numbered from 0 to N. The largest possible TIFF file is 2**32 bytes in length. A TIFF file begins with an 8-byte
image file header that points to an image file directory (IFD). An image file directory contains information about the
image, as well as pointers to the actual image data.
A TIFF file structure is shown in Figure 1.
Figure 1 — TIFF file structure
4.1.1 Image file header
A TIFF file begins with an 8-byte image file header, containing the following information:
Bytes 0-1: The byte order used within the file. Legal values are:
II (4949.H)
MM (4D4D.H)
In the II format, byte order is always from the least significant byte to the most significant byte, for
both 16-bit and 32-bit integers. This is called little-endian byte order. In the MM format, byte order is
always from the most significant byte to the least significant byte, for both 16-bit and 32-bit integers.
This is called big-endian byte order.
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ISO 12234-2:2001(E)
Bytes 2-3: An arbitrary but carefully chosen number (42) that further identifies the file as a TIFF file.
The byte order depends on the value of Bytes 0-1.
Note that, in order to allow backward compatibility with future versions of TIFF/EP based on future
versions of TIFF, all TIFF/EP readers should test the TIFF header version value to determine if
VERSION >= 42, not to test if VERSION == 42. This will allow higher version numbers to be used in
the future and to be detected as TIFF/EP files.
Bytes 4-7: The offset (in bytes) of the first IFD. The directory may be at any location in the file after the header
but shall begin on a word boundary. In particular, an image file directory may follow the image data
it describes. Readers shall follow the pointers wherever they may lead.
The term byte offset is always used in this part of ISO 12234 to refer to a location with respect to the
beginning of the TIFF file. The first byte of the file has an offset of 0.
4.1.2 Image file directory (IFD)
An IFD consists of a 2-byte count of the number of directory entries (i.e. the number of fields), followed by a
sequence of 12-byte field entries, followed by a 4-byte offset of the next IFD (or 0 if none). Do not forget to write
4 bytes of 0 after the last IFD.
There shall be at least 1 IFD in a TIFF file and each IFD shall have at least one entry.
4.1.2.1 IFD entry
Each 12-byte IFD entry has the following format:
Bytes 0-1: The tag that identifies the field.
Bytes 2-3: The field type.
Bytes 4-7: The number of values, Count of the indicated type.
Bytes 8-11: The value offset, i.e. the file offset (in bytes) to the value(s) for the field. This value offset is
expected to begin on a word boundary; the corresponding value offset will thus be an even
number. This file offset may point anywhere in the file, even after the image data. (See below for
more information.)
4.1.2.2 IFD terminology
A TIFF field is a logical entity consisting of a TIFF tag and its value. This logical concept is implemented as an
IFD entry, plus the actual value if it doesn’t fit into the value/offset part, the last 4 bytes of the IFD entry.The terms
TIFF field and IFD entry are interchangeable in most contexts.
4.1.2.3 Sort order
The entries in an IFD shall be sorted in ascending order by tag. The values to which directory entries point need not
be in any particular order in the file.
4.1.2.4 Value/Offset
To save time and space, the value offset contains the value instead of pointing to the value only if the value fits into
4 bytes. If the value is shorter than 4 bytes, it is left-justified within the 4-byte value offset, i.e. stored in the lower-
numbered bytes. Whether the value fits within 4 bytes is determined by the type and count of the field.
Note that the 4 byte value offset should not be thought of as a LONG data type since, if the value is shorter than
4 bytes, it is always left-justified regardless of whether the II or MM byte order is used. For example, to store the
SHORT hex value “AB CD” in MM byte order, the 4 bytes are “AB CD xx xx” (where x indicates “don’tcare”). The
samehex valueinII byteorder is given by “CD AB xx xx”.
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ISO 12234-2:2001(E)
4.1.2.5 Count
Count, called Length in previous versions of the TIFF specification, is the number of values. Note that count is not
the total number of bytes. For example, a single 16-bit word (SHORT) has a count of 1 not 2.
4.1.2.6 Types
The field types and their sizes are:
1=BYTE 8-bit unsigned integer.
2=ASCII 8-bit byte that contains a 7-bit ASCII code; the last byte shall be NUL (binary zero).
3=SHORT 16-bit (2-byte) unsigned integer.
4=LONG 32-bit (4-byte) unsigned integer.
5=RATIONAL Two LONGs: the first represents the numerator of a fraction, the second represents the
denominator.
6=SBYTE An 8-bit signed (twos-complement) integer.
7=UNDEFINED An 8-bit byte that may contain anything, depending on the definition of the field.
8=SSHORT A 16-bit (2-byte) signed (twos-complement) integer.
9=SLONG A 32-bit (4-byte) signed (twos-complement) integer.
10=SRATIONAL Two SLONGs: the first represents the numerator of the fraction, the second represents the
denominator.
11=FLOAT Single precision (4-byte) IEEE format.
12=DOUBLE Double precision (8-byte) IEEE format.
WARNING — It is possible that other TIFF field types will be added in the future. Readers should ignore
fields containing an unexpected field type.
The value of the count part of an ASCII field entry includes the NUL. If padding is necessary, the count does not
include the pad byte. Note that there is no initial count byte as in Pascal-style strings. Any ASCII field can contain
multiple strings, each terminated with a NUL. A single string is preferred whenever possible. The count for
multistring fields is the number of bytes in all strings in that field plus their terminating NUL bytes. Only one NUL is
allowed between strings, so that the strings following the first string will often begin on an odd byte.
The reader shall check the type to verify that it contains an expected value. TIFF currently allows more than 1 valid
type for some fields. For example, ImageWidth and ImageLength are usually specified as having type SHORT. But
images with more than 64K rows or columns shall use the LONG field type. TIFF readers should accept BYTE,
SHORT or LONG values for any unsigned integer field. This allows a single procedure to retrieve any integer value,
makes reading more robust and saves disk space in some situations.
Each TIFF field has an associated count. This means that all fields are actually one-dimensional arrays, even
though most fields contain only a single value. For example, to store a complicated data structure in a single private
field, use the UNDEFINED field type and set the count to the number of bytes required to hold the data structure.
4.1.3 Vendor unique information
Each camera manufacturer may choose to store additional information in the form of private tags or private tag-
values. This can be done by obtaining private tags and/or tag-values for TIFF 6.0 tags from the Adobe Developers
Desk and vendor unique tag-values from PIMA/IT10 for the new TIFF/EP defined tags. When storing additional
vendor unique information within TIFF/EP files, care shall be taken not to violate the TIFF/EP guidelines described
in this part of ISO 12234.
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ISO 12234-2:2001(E)
4.2 Image data
The image width, i.e. horizontal or X dimension, is recorded as a binary value in the ImageWidth tag-field. The
image width may be the shorter or longer dimension of the image, depending upon the orientation of the camera
during image capture. The image orientation is defined by the Orientation tag-field. The image length, i.e. vertical
or Y dimension, is recorded as a binary value in the ImageLength tag-field. The camera’s desired image output
rendering resolution in the X-dimension, i.e. the horizontal dimension when the camera is normally oriented, is
recorded using the XResolution tag-field, while the output resolution in the Y-dimension is recorded in the
YResolution tag-field. The ResolutionUnits tag-value gives the units for the XResolution and YResolution
values. These mandatory TIFF 6.0 tag-fields are typically used to determine the default size of the image on the
screen. They do not indicate the sample spacing of the image sensor in an electronic still-picture camera. The latter
is giveninthe FocalPlaneXResolution, FocalPlaneYResolution and FocalPlaneResolutionUnits tag-values.
The pixel aspect ratio (ratio of the pixel width to pixel height) is determined by the ratio of the XResolution and
YResolution values. The recommended TIFF/EP pixel aspect ratio is 1:1 (square), so that XResolution equals
YResolution.
The number of colour components or samples per pixel in the image is recorded using the SamplesPerPixel tag-
field as a binary value. For example, an image captured using a monochrome sensor has only one colour
component or sample per pixel, while a 3-sensor colour RGB camera has three colour components or samples per
pixel. The number of bits needed to store each of the colour components (samples) is recorded using the
BitsPerSample tag-field as a set of binary values. In the case of a monochrome image, the BitsPerSample tag-
field contains only one value, equal to the actual number of bits per pixel. In the case of an RGB image having
three colour samples per pixel, the BitsPerSample tag-field contains three values equal to the actual number of
bits of storage used to store each component or sample. In the latter case, the number of bits for each colour-
component could be different and hence is explicitly stated.
The type of image data components are provided by the PhotometricInterpretation tag-value. All TIFF/EP
readers shall handle greyscale, RGB and YCbCr data. If YCbCr data values are stored, the number of Cb and Cr
values may either be equal to the number of Y values or smaller owing to subsampling. The chrominance
subsampling factors of a YCbCr image are encoded in the YCbCrSubSampling tag-field. This tag-field contains
both the horizontal and vertical subsampling factors, which are labelled YCbCrSubSamplingHoriz and
YCbCrSubSamplingVert respectively. The subsampling factors are given relative to the appropriate dimension of
the corresponding luminance image. The positions of the subsampled chrominance components relative to the
luminance samples are encoded in the YCbCrPositioning tag-field. The headroom/footroom image data values
(codes) for each each pixel component associated with a YCbCr image is specified within the
ReferenceBlackWhite tag-field. The pair of headroom/footroom values (codes) associated with the luminance
component (Y) refer to this component’s ReferenceWhite and ReferenceBlack. The pair of headroom/footroom
values (codes) associated with the chrominance components, Cb and Cr, refer to these components'
ReferenceBlack and ReferenceWhite, where here the ReferenceWhite value is used to code reference blue and
reference red respectively.
The image data may optionally be stored using a single image component having a colour filter array (CFA) area
pattern of the image data derived from a single-chip colour CCD image sensor. TIFF/EP readers are not required to
handle this type of image data. The colour filter array area pattern is the repetitive spatial colour sampling pattern of
photosites on the CCD image sensor. There are many different CFA-type CCDs which capture only one colour
component per photosite on the CCD. The tags used to describe a CCD’s CFA pattern are: SamplesPerPixel,
PlanarConfiguration, CFARepeatPatternDim, CFAPattern and SensingMethod.
The image data is stored using either strips or tiles, which are collectively termed segments. If strips are used, the
following tag-fields define the number of strips and the number of rows of image data stored in each strip:
StripOffsets, RowsPerStrip and StripByteCounts. The image shall be divided into an integral number of strips,
from one strip to the maximum number of strips, which equals the image’s length. If necessary, the final strip can
be “padded” with zeros. TIFF/EP recommends that the image data, prior to compression, does not exceed
64 Kbytes per strip. This value is chosen to maximize compatibility with various operating systems. The
StripOffsets tag-field stores the offsets from the start of the image file to the start of each image data strip. In this
way, the reader can easily access various parts of the image. The number of rows per strip is stored in the
RowsPerStrip tag-field. The number of image data bytes stored within each strip is recorded in the
StripByteCounts tag-field. The “strip” mechanism is very useful in accessing images, because it uses less buffer
memory than would otherwise be needed to read in the entire image all at one time. The order of the image strips is
from the top to the bottom of the image.
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ISO 12234-2:2001(E)
EXAMPLE ImageWidth = 768
ImageLength = 512
PhotometricInterpretation = 2 (RGB)
SamplesPerPixel = 3
BitsPerSample = 8,8,8
PlanarConfiguration = 1 (Chunky),
...