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File: Image/ExifTool/README
Description: ExifTool support modules documentation
The ExifTool support modules are loaded by ExifTool to allow processing of
various meta information formats.
The tables in these files are used as lookups based on the tag ID values. The
hash keys are the tag IDs (in decimal or hexadecimal if the ID is numerical as
with EXIF tables, or the tag name if the ID is ASCII as with XMP tables). In
the case of a BinaryData table, the IDs are numerical and specify offsets into
the binary data block (floating point IDs allow multiple tags for the same
offset, with the integer part being used for the offset). The corresponding
hash value provides information about the tag (explained later).
Twenty-six special keys (TABLE_NAME, SHORT_NAME, PROCESS_PROC, WRITE_PROC,
CHECK_PROC, GROUPS, FORMAT, FIRST_ENTRY, TAG_PREFIX, PRINT_CONV, WRITABLE,
TABLE_DESC, NOTES, IS_OFFSET, IS_SUBDIR, EXTRACT_UNKNOWN, NAMESPACE, PREFERRED,
SRC_TABLE, PRIORITY, AVOID, WRITE_GROUP, LANG_INFO, VARS, DATAMEMBER and
SET_GROUP1) are used to provide additional information about a table. The
special keys have names that are all capitalized to avoid possible conflicts
with tag keys. Below is an explanation of the meaning of each special key:
TABLE_NAME : Name of this table (set automatically by GetTagTable()).
SHORT_NAME : Table name with leading "Image::ExifTool::" removed.
PROCESS_PROC : Reference to a function used to process the directory for this
table. If PROCESS_PROC is not given, \&Image::ExifTool::Exif::ProcessExif is
assumed (except for QuickTime atoms for which
\&Image::ExifTool::QuickTime::ProcessMOV is the default). If PROCESS_PROC is
set to 0, the tags are not added to the lookup. The process proc returns 1 on
success or 0 on failure, and takes 3 arguments: 0) reference to the ExifTool
object, 1) reference to a directory information hash (with the following
entries:), 2) reference to the tag table hash.
Name - Tag name for this SubDirectory entry (for verbose messages)
Base - Base offset for pointers from start of file
DataPt - Reference to data block containing directory (may be undef)
DataPos - Position of data block within file (relative to Base)
DataLen - Length of data block in bytes
DirStart - Offset to start of directory from start of data block
DirLen - Length of directory data within block
DirName - Name of this directory
OutFile - Output file or scalar reference
Parent - Name of parent directory
RAF - Reference to File::RandomAccess object if available
NewDataPos - File position of new data (write proc only)
Fixup - Reference to hash of offset fixups (used in EXIF writing only)
FixBase - Flag set to attempt to fix base offsets
FixOffsets - Evaluated for each value pointer to patch maker note offsets
LastIFD - Used by WriteExif() to return offset of last IFD written
ImageData - Used by WriteExif() to avoid buffering large image data blocks
WRITE_PROC : Reference to a function to write all new tags for this directory.
The write proc returns the new directory data or undefined on error. It takes
the same arguments as the process proc above except that the second argument
(reference to directory information hash) is optional, and if specified gives
information about the source directory for tags to be copied to the output.
CHECK_PROC : Reference to a function which validates Raw values for writing.
The function takes three arguments: 0) ExifTool object reference, 1) tagInfo
reference, 2) value reference, and returns undefined (and possibly modifies
the input value) if successful, or an error message if there was a format
problem. May set ExifTool CHECK_WARN datamember for success with a warning.
GROUPS : A hash lookup for the default group names for all entries in this
table. If not specified, the default Group 0 and 1 names will be set
automatically according to the name of the module, and the default Group 2
name will be set to 'Other'.
FORMAT : Specifies the default tag Format, and corresponding pointer increment
for entries in a BinaryData table. Defaults to 'int8u' for BinaryData tables
if not specified. The possible values of FORMAT are:
int8s - Signed 8-bit integer (EXIF 'SBYTE')
int8u - Unsigned 8-bit integer (EXIF 'BYTE')
int16s - Signed 16-bit integer (EXIF 'SSHORT')
int16u - Unsigned 16-bit integer (EXIF 'SHORT')
int16uRev - Unsigned 16-bit integer, reversed byte order
int32s - Signed 32-bit integer (EXIF 'SLONG')
int32u - Unsigned 32-bit integer (EXIF 'LONG')
int64s - Signed 64-bit integer (BigTIFF 'SLONG8')
int64u - Unsigned 64-bit integer (BigTIFF 'LONG8')
rational32s - Rational consisting of 2 int16s values
rational32u - Rational consisting of 2 int16u values
rational64s - Rational consisting of 2 int32s values (EXIF 'SRATIONAL')
rational64u - Rational consisting of 2 int32u values (EXIF 'RATIONAL')
fixed16s - Signed 16-bit fixed point value
fixed16u - Unsigned 16-bit fixed point value
fixed32s - Signed 32-bit fixed point value
fixed32u - Unsigned 32-bit fixed point value
float - 32-bit IEEE floating point value (EXIF 'FLOAT')
double - 64-bit IEEE floating point value (EXIF 'DOUBLE')
extended - 80-bit extended floating float
ifd - Unsigned 32-bit integer sub-IFD pointer (EXIF 'IFD')
ifd64 - Unsigned 64-bit integer sub-IFD pointer (BigTIFF 'IFD8')
string - Series of 8-bit characters (EXIF 'ASCII')
undef - Undefined-format binary data (EXIF 'UNDEFINED')
binary - Binary data (same as 'undef')
Additionally, the following variable-length Format types may be used in
individual tag information hashes of a BinaryData table. The 'var_' formats
cause subsequent tag indices to be incremented according to the size of the
data, not including the terminator. See "Format" below for more details.
pstring - Pascal string (1-byte length followed by ASCII string)
var_string - variable-length null-terminated ASCII string
var_ustring - variable-length null-terminated UCS-2 string
var_pstring - variable-length Pascal string
var_pstr32 - variable-length Pascal string /w 32-bit len
var_ustr32 - variable-length UCS-2 string /w 32-bit len
var_int16u - variable-length undef data with int6u count
var_ue7 - variable-length 7-bit-at-a-time integer (BPG)
And the following format codes are used for string values in XMP metadata.
(See the XMP specification for more details.)
boolean - "True" or "False"
date - date/time string
integer - integer as a string
lang-alt - list of alternate-language strings
rational - "N/D" where N=numerator, D=Denominator
real - floating point value as a string
string - unformatted string
struct - structure
FIRST_ENTRY : Specifies the index for the first tag entry in a binary table.
This value is only used if the Unknown option is set to 2 or higher, and
allows the binary data to be scanned for unknown tag entries.
TAG_PREFIX : Prefix for names of unknown tags.
PRINT_CONV : Default print conversion for tags where PrintConv isn't
specified. PrintConv may be set to undef for individual tags to disable print
conversion when PRINT_CONV is defined for a table.
WRITABLE : Indicates that all tags in this table are writable. This is the
same as setting the Writable flag for each individual tag in the table, except
for SubDirectory tags which are not made Writable.
TABLE_DESC : Short description for this table. Plain text only. Used only
for XML tag database output.
NOTES : Notes to introduce the table in the TagNames documentation. Pod
formatting codes B<>, C<> and L<> may be used in this text.
IS_OFFSET : Writable BinaryData tables only. Reference to list of sorted
TagID's representing offsets.
IS_SUBDIR : Writable BinaryData tables only. A reference to a list of sorted
tag ID's representing subdirectories.
EXTRACT_UNKNOWN : Used in PDF tables to specify a directory where all unknown
tags should be extracted. Set to 0 to extract only unknown numbered tags for
which the unnumbered tag is known.
NAMESPACE : Namespace prefix for tags in the XMP table. If this isn't a
standard namespace defined in %Image::ExifTool::XMP::nsURI, then the URI must
be defined as well (however, this is not recommended for pre-defined
namespaces because then non-standard namespace prefixes won't be recognized).
To define the URI, the NAMESPACE value is a reference to a hash where the key
is the namespace prefix and and the value is the URI (alternatively, a
reference to a 2-element array containing the prefix and URI is also allowed
for backward compatibility). The NAMESPACE value may be undef for XMP tables
where tags have variable namespaces (in this case each tag must have a
Namespace entry).
PREFERRED : Set to true if the tags in this table should always be added when
writing information. Overrides the order specified by SetNewGroups(). When
this feature is used, it may also be desireable to specify a preferred group
when calling InitWriteDirs() to write these tags; this avoids creating other
directories for tags which are already being creating in the preferred group.
SRC_TABLE : Used internally to store the source table name of a user-defined
tag table so the appropriate module can be loaded as required.
PRIORITY : Default Priority for all tags in this table.
AVOID : Flag set to Avoid writing all tags in this table.
WRITE_GROUP : Default WriteGroup for all tags in the table.
LANG_INFO : Code reference to a routine which returns a reference to a
language-specific tag information hash. The routine takes two arguments: a
reference to the non-specific tagInfo hash, and the language code. Used only
in tables with writable tags which support tag name language extensions (eg.
MIE and XMP).
VARS : Hash used to store additional parameters. Individual modules may use
this to store any parameters they want. The following additional parameters
have been defined, and may be used by any module:
ID_LABEL Label to use instead of "Tag ID" for column heading in tag
name documentation. When this is set, numerical TagID's are
not converted to hexadecimal notation. Unless otherwise set,
an ID_LABEL of "Index" is assumed for tables which use
ProcessBinaryData.
NO_ID Avoid printing "Tag ID" column in tag name documentation.
HEX_ID Print tag ID in hexadecimal (with 4 hex digits or more).
NO_LOOKUP Do not add tags to TagLookup.pm lookup tables.
CAPTURE Used by PDF module to name dictionaries to capture when
writing.
MINOR_ERRORS [EXIF tables only] Flag to make errors in this IFD minor, or
to downgrade already minor errors to warnings while writing.
(Errors in MakerNote IFD's are already classified as minor.)
Note that for certain types errors, the response is to delete
the entire IFD from the image.
ALPHA_FIRST Sort alphabetical tags before numerical in documentation.
LONG_TAGS Suppress "Long tags" warning when generating documentation.
Value is the number of long tag names to expect.
SORT_PROC Reference to sort procedure for sorting tag ID's in the
documentation. Takes two arguments and returns -1, 0 or 1
if the first argument is less than, equal to, or greater than
the second argument.
ENTRY_SIZE Used by ProcessPhaseOne to specify size of IFD entry
MAP_FORMAT Lookup to map unknown format numbers (eg. Panasonic CameraIFD)
START_INDEX [QuickTime tables only] Initial index for indices shown in
Verbose output. Indices are not show otherwise.
DATAMEMBER : BinaryData tables only. A reference to a list of sorted tag ID's
which must be extracted as data members when writing. Must also list "var_"
format tags and tags with Hook so offsets are properly calculated if the table
is writable.
SET_GROUP1 : [EXIF tables only] Flag to set group1 name to the directory name
for all tags in the table.
The remaining entries in a tag table are the tag IDs with their associated
information. The information may exist in one of three forms: 1) A simple
scalar which is the name of the tag, 2) A reference to a hash of information
describing this tag, or 3) a reference to a list of hashes which contain
Condition expressions allowing the appropriate hash to be selected to suit the
conditions. The following is a description of possible hash entries. All
entries are optional, except for the tag Name which is required if the tag ID is
numerical.
Name : The tag name. Tag names need not be unique. If they aren't
unique, then duplicate tags will hide the values of previous
tags when extracting information unless the Duplicates option
is set or the new tag has lower Priority. With Duplicates
set, to allow multiple tags with the same name to exist in the
tag information hash, the key of the previous tag is changed
to the form "TagName (N)", where N starts at 1 and increments
for subsequent duplicate tags. A tag name should start with
an uppercase letter, and contain only the characters in the
set [A-Za-z0-9_-]. If not given, the Name is taken from the
tag ID with the first character changed to upper case.
Description : A more readable description of tag name. If a tag doesn't
specify a Description, then the tag Name is used instead, with
spaces inserted between the words.
Notes : Notes for this tag in the HTML TagNames documentation.
Groups : Hash lookup for group names for this tag. If not specified,
defaults to the GROUPS specified in the table definition.
Format : Only valid for BinaryData, EXIF and IPTC tables. For a Binary
or EXIF table, this gives the format that is used to convert
the binary data, and is one of the FORMAT types specified
above. If not specified, the Format of an EXIF entry is taken
from the EXIF information, and the Format of a BinaryData
entry is taken from the FORMAT specified for the table (or
int8u if FORMAT is not specified). Must be specified for
Writable tags where the value must be converted for a
Condition. For BinaryData tables, the format may have a size
in trailing brackets which is a Perl expression to be
evaluated. The expression may access any of the previous
table entries through a %val hash (read-only tags), the data
size via $size, or the ExifTool object via $self. For
example, 'string[$val{3}]' defines a string with length given
by the table entry with tag index '3'. An initial "var_" may
be added to the Format name of any BinaryData tag with a size
in brackets. In this case, subsequent offsets are adjusted by
the value length minus the size of the default table FORMAT
(eg. "var_int16u[10]" causes subsequent offsets to be
incremented by sizeof(int16u) * 10 - sizeof(int8u) if the
default table FORMAT is "int8u"). Note that all "var_" Format
tags (as well as tags with values used within "var_" Format
expressions) must have corresponding DATAMEMBER entries.
Count : Used when writing EXIF information to specify the number
values to write, or the number of characters in a fixed-length
string. A value of -1 indicates that the count is variable
and should be determined by the number of values provided.
Defaults to 1 if not specified for non-string formats. Note
that this count corresponds to the specified Format, so if a
different-sized Writable format is defined, the actual count
written to the file will be different.
FixCount : Flag set to determine correct count from offsets in IFD. This
is necessary for some Kodak tags which write an incorrect
Count value.
Flags : Flags to specify characteristics for this tag. May be a
simple scalar flag name, a reference to a list of flag names,
or a reference to a hash of flag/value pairs. If not a hash
reference, the flag value is set to 1. Flags are expanded for
faster access at run time into members of the tagInfo hash,
and may be written directly as members if desired. The
available flag names are:
'AutoSplit' - [List tags only] Similar to ListSplit option,
but applied automatically to individual tags. Value specifies
pattern for split, or 1 for default pattern ',?\\s+'.
'Avoid' - avoid creating this tag if possible. This is only
effective if another tag exists with the same name. Setting
this flag also sets the default Priority to 0 for this tag.
'Binary' - set to 1 for binary data. This has the same effect
as setting ValueConv to '\$val', but it it a bit cleaner and
avoids dummy ValueConvInv entries for writable tags. Has no
effect if ValueConv is defined for the tag. Some values may
be treated as binary data even if this flag is not set.
'BlockExtract' - set for writable directories in EXIF
information which are extracted by default. Otherwise
writable directories are only extracted as a block if
specified explicitly. Also used for Jpeg2000 and QuickTime
XMP-like tags to extract as a block with a name other than
'XMP'.
'ConvertBinary' - true to apply ValueConv and/or PrintConv to
Binary values (ie. SCALAR references). (By default, these
conversions are not done for Binary values.)
'DataMember' - name of exiftool data member associated with
this tag if it should be stored as a special data member when
writing information. Necessary only if the value of the tag
affects other written information. Currently only used for
tags in EXIF tables where it triggers the execution of the
RawConv to convert and store the value as an ExifTool data
member when writing.
'DataTag' - associated tag name containing data for offset or
byte count tags.
'Drop' - [IFD-format and PhaseOne makernote tags only] set to
1 for tags that should be excluded when rebuilding maker notes
when copying all tags. Set to a number larger than 1 to drop
only if data is larger than this size. Works for SubDirectory
tags too.
'EntryBased' - set to 1 if the offset for this value is based
on the IFD entry position. This allows individual values to
be entry-based even though some others aren't (as with the
Casio PrintIM information).
'Flat' - [flattened XMP structure tags only] must be set for
all pre-defined flattened tags (including user-defined
flattened tags). This flag is reset to 0 internally after all
associated flattened tags in the structure have been
generated.
'Flattened' - [reserved] used internally to mark Struct tags
which have been processed to generate flattened equivalents.
'GotGroups' - [reserved] flag used internally to indicate that
the Groups hash has been initialized for this tag.
'Hidden' - set to hide tag from the TagName documentation.
Also suppresses verbose output of a BinaryData tag.
'IsComposite' - flag set for Composite tags
'IsOffset' - flag set if the tag represents an offset to some
data, and causes value will be adjusted to an absolute file
offset. If set to 2, the offset base of the parent directory
is used even if the base changes for the current directory
(only some maker notes are this messed up). Set to 3 if
absolute file offsets are used. May be set to an expression
to be evaluated. Expression may access $val and $et,
and is evaluated only when reading.
'List' - flag indicating that duplicate entries of this tag
are allowed, and will be accumulated in a list. Note that for
XMP information, 3 different types of lists are supported and
the List value specifies the type: 'Bag', 'Seq' or 'Alt'. As
well, a value of '1' is used internally in XMP to allow list
behaviour for a flattened tag which is itself not a list
element (eg. a member of list of structures). Note that in
ExifTool an XMP lang-alt tag (Writable="lang-alt") is NOT a
list-type tag (unless it is a list of lang-alt lists, which is
uncommon).
'MakerNotes' - set if this tag is maker note data.
'MakerPreview' - set in the PreviewImageStart tag information
if the preview must be stored inside the maker notes.
'Mandatory' - set for mandatory tags. Used only by TagInfoXML
and for documentation purposes. Mandatory tags may be added
automatically by ExifTool.
'NestedHtmlDump' - flag set if value for this tag is also
dumped when processing the SubDirectory. This flag is implied
if the MakerNotes flag is set. Set to 2 if the dump should
only be underlined if nested inside other maker notes.
'NotIFD' - set for 'MakerNotes' SubDirectory tags only if the
SubDirectory is not EXIF IFD format. (Note: All SubDirectory
tags in the MakerNotes table are 'MakerNotes' type by
default.)
'OffsetPair' - set if the tag represents half of an offset/
byte count pair. Data for these tags must be handled
separately. Value is the tagID for the paired tag.
'Permanent' - flag indicates that a tag is permanent, and
can't be added or deleted from the file, although a new value
may be written if the tag already exists. By default, all
MakerNotes tags are permanent unless otherwise specified.
'PrintHex' - specifies that unknown PrintConv values should
be printed in hex (eg. 'Unknown (0x1)'). Also causes
numerical tag values to be printed in hex in the HTML tag name
documentation, padded to the number of digits given by the
PrintHex value.
'PrintSort' - causes PrintConv values to be sorted by value
rather than key in the HTML tag name documentation.
'PrintString' - flag set to force PrintConv values to be
printed as strings in the documentation.
'Priority' - gives the priority of this tag while reading. If
set to zero, this tag will not override the value of previous
tags with the same name. If the priority is greater than
zero, this tag won't be overridden by subsequent tags unless
their priority is equal to or greater than this priority. A
special feature is that Priority 0 tags are automatically
incremented to Priority 1 if they exist in the IFD of the full
resolution image (as determined by SubfileType). If not
defined, the priority defaults to 1 for all tags except except
tags in IFD1 of JPEG images which default to priority 0.
'Protected' - bit mask to protect tags from writing:
Bit 0x01 indicates an 'unsafe' tag, which is not set via
SetNewValuesFromFile() unless specified explicitly.
Bit 0x02 indicates a 'protected' tag, which should not be set
directly by the user.
'PutFirst' - [EXIF only] flag to place this value before IFD0
when writing (ie. immediately after TIFF header). Only used
for main IFD's (IFD0, IFD1, etc) and IFD's where SubIFD flag
is set to 2 (currently only ExifIFD).
'RawJoin' - [List tags only] Joins raw List-type tag values
into a single string with a space separator, allowing
ValueConv and PrintConv to act on the concatenated string so
the tag does not exhibit list-type behaviour. When writing,
the inverse is performed and the value is split at whitespace.
'Resource' - [XMP only] flag to write value as an rdf:resource
in an empty element instead of as a normal string.
'SeparateTable' - set to list PrintConv values in a separate
table in the HTML documentation. Value is 1 for a table name
of 'Module TagName', or 'TAG' for 'Module TAG', or 'MODULE
TAG' to fully specify the table name. The table may have a
'Notes' entry for a description of the table.
'SetResourceName' - [Photoshop tags only] set to 1 to append
resource name to the extracted value (eg. 'VALUE/#NAME#/').
Also allows resource name to be appended when writing new
values. May be set to any value other than 1 for a default
resource name to use when writing if an appended name is not
provided.
'StructType' - [reserved] used internally by XMP writer for
flattened structure tags as a flag to indicate that one or
more enclosing structures has a TYPE field.
'SubDoc' - [Composite tags only] set to cause this Composite
tag to also be generated for each sub-document. To achieve
this, 'Main:' and 'Doc#:' prefixes are added to all Require'd
and Desire'd tag names which don't already start with 'Main:'
or 'Doc#:', and the Composite tag is built once for each of
the main document and all sub-documents. May be a reference
to a list of indices for Desire'd tags, one of which must
exist to generate this tag for sub-documents.
'SubIFD' - used in writing to determine that the tag specifies
an offset to a sub-IFD. When this flag is set, the Group1
name gives the name of the IFD. Must be set if and only if
the tag has a SubDirectory Start that references '$val' (this
is validated by BuildTagLookup). Set to 2 for standard EXIF
SubIFD's where the PutFirst flag is valid.
'Unknown' - this is an unknown tag (only extracted when the
Unknown option is set).
'WriteNothing' - flag indicating that nothing is actually
written when this tag is set. It is a fake writable tag that
isn't actually written (eg. Geotag). Used to avoid processing
a file unnecessarily if nothing will actually be written.
'WritePseudo' - flag indicating that this is a writable pseudo
tag. If set, this tag may be written without actually writing
to the file (eg. FileName, FileModifyDate).
'WrongBase' - ['IsOffset' tags only] An expression using $self
that is evaluated to generate a base shift for 'IsOffset' tags
which use a different base than the rest of the tags.
RawConv : Used to convert the Raw value at extraction time (while the
image file is still open, unlike ValueConv and PrintConv below
which are done later only if the value is requested). May be
a scalar expression using $val (the Raw tag value), $self (the
current ExifTool object), $tag (the tag key), $tagInfo
(reference to the tag information hash), $priority (to
dynamically set the priority of a tag), and @grps (to
dynamically set the family and/or groups), or a code reference
with $val and $self as arguments (in which case $$self{grps}
may be used to set the groups). For Composite tags, $val is a
reference to a hash of source ("derived from") tag names, and
@val may be used to access the Raw values of these tags. The
returned value may be a scalar which is used as the new Raw
value, a scalar reference to a binary data value, a hash
reference for Composite tags, an ARRAY reference for a list of
values, or undefined to indicate that the tag should be
ignored. If RawConv is specified for a Composite tag, then
ValueConv and PrintConv evals will no longer have access to
the source @val and @prt values unless the input $val is
returned. RawConv may generate Warning or Error tags, while
ValueConv and PrintConv should not (see ValueConv note below).
Note: RawConv should only be used if necessary (in general,
only if the conversion may return undef to ignore the tag, or
if a Warning may be issued) because ValueConv is more
efficient since it is only executed if the tag value is
requested, while RawConv is executed for all extracted tags.
ValueConv : Used to convert the Raw value to a useable form. May be a hash
reference to act as a lookup table, a scalar which is
evaluated as a Perl expression, a code reference to a
subroutine, or an ARRAY reference (in which case the value is
split at whitespace into a list of items and each item is
converted by the associated entry in the ValueConv list. A
special value of 'REPEAT' may be used to repeat the previous
conversion for all remaning elements). If a hash reference is
used and the Raw value doesn't appear as one of the keys, then
the converted value is set to "Unknown (X)", where X is the
Raw value (unless either of the special keys exist: 'BITMASK',
a reference to a hash used to decode individual value bits; or
'OTHER', a reference to a subroutine used to convert unknown
values. The OTHER subroutine takes 3 arguments: the value, a
flag which is set for the inverse conversion, and a reference
to the PrintConv hash, and returns the converted value or
undef on error -- it may call warn() to return an error
message. The lookup hash may also contain a 'Notes' entry
which is used for documentation if the SeparateTable flag is
set). In an expression, $self is a reference to the current
ExifTool object, $val is the Raw value, and $tag is the tag
key. The subroutine takes 2 arguments: the Raw value and a
reference to the current ExifTool object. The advanced
formatting expression (if any) may be accessed via the
ExifTool "FMT_EXPR" member variable. The expression or
subroutine is evaluated if and when the tag value is requested
(ie. only after all extraction is complete), so if necessary
at this time the values of all other tags are available via
calls to $self->GetValue("Tag","Raw"). (Note: In theory,
types other than "Raw" may be accessed, but they are slower
and may lead to cyclical dependencies so they should be
avoided). When evaluated, the expression or subroutine
returns a scalar for the converted value, a SCALAR reference
to a binary data value (see the 'Binary' flag), or an ARRAY
reference for a list of values. The return value should
always be defined -- use RawConv instead to return undef if it
is necessary to test the value for validity, otherwise an
undef tag may hide a previously defined value when the
Duplicates option is not enabled. If this isn't possible (as
with Composite tags where the converted values of the source
tags are needed), set the Priority to 0 to avoid taking
priority over a valid tag. If ValueConv is not specified, the
Raw value is not converted. Composite tags which Require or
Desire other tags may access the ValueConv, PrintConv and Raw
values of these tags through the elements of the @val, @prt
and @raw lists respectively (only if there was no RawConv or
it returned a hash reference). For these tags, $val may be
used in an expression to represent $val[0], and the first
argument passed for a code reference is a reference to @val.
Note: Warnings issued by these conversions are intercepted by
ExifTool and saved as Warning tags, but since ValueConv and
PrintConv conversions are done on demand, the warnings may be
generated after the list of extracted tags is returned, so may
easily be missed.
PrintConv : This entry is similar to ValueConv above, except that it is
used to further convert the tag value to a human readable
form. It can be either a hash lookup, a scalar Perl
expression, a code reference or a list reference. In this
expression, $self, $val and $tag may be used as with
ValueConv, but if ValueConv was defined then $val is the
ValueConv value instead of the Raw value. The returned value
should always be defined. Note that the print conversion is
only done if the PrintConv option is enabled (which it is by
default), and if the result of the ValueConv is not a scalar
reference. If it is a list reference, then the converted
values are joined by '; ' in the output string.
RawConvInv : The inverse of RawConv. This should only be used in very rare
situations when the raw value can not be predetermined.
Unlike the other inverse conversions which are applied in
SetNewValue(), this conversion is applied in WriteInfo() as
the file is being written. This is important because it means
that FILE_TYPE and any DataMember tags ocurring before this
tag in the file are available. Beware that if the return
value is not defined, the tag will be deleted unless there is
specific logic to avoid this (currently, only EXIF and Binary
data directories handle this case).
ValueConvInv : The inverse of ValueConv. Only necessary for Writable tags
when ValueConv is specified (except WriteAlso tags). Note
that DataMember tags may NOT be used in the inverse
conversions because these conversions are done before the
input file is parsed. Instead, a Condition or RawConvInv must
be used. May return undef on conversion error and call warn()
to issue a warning. If warn() is not called, a generic
warning is generated when undef is returned. An empty warning
("\n") may be issued to suppress warning messages when undef
is returned. If a scalar, the expression may use the
variables $val, $self and $wantGroup. If a code ref, the
routine is passed 2 arguments: $val and $self. Note that this
conversion is not applied for deleted tags (ie. $val is
undef).
PrintConvInv : The inverse of PrintConv. Necessary for Writable tags
when PrintConv is specified (unless WriteAlso is used), but
may be used without PrintConv. See ValueConvInv above for
more details.
PrintConvColumns : Number of columns for PrintConv lookup in HTML docs. If not
set, the number of columns is determined automatically
according to the maximum width of the entries.
DelValue : Raw value to be used when deleting a permanent tag. (Note all
MakerNotes tags are permanent.) If not specified, an attempt
is made to convert an empty string for the raw value.
Validate : Scalar expression used to validate the raw value of a tag when
the Validate option is set. The expression may access $val
(the Raw tag value), $tag (the tag key) and $self (the current
ExifTool object), and should return a warning if any problem
is found, or false if OK. The evaluation is performed in the
Image::ExifTool::Validate package namespace, so functions of
this package need not be prefixed by the package name.
Relist : [Only if ValueConv or PrintConv is a list ref] Reference to a
list of original value indices used to reorganize values. Each
entry in the list may be a scalar index, or a reference to a
list of indices to join values. (Currently values may be
joined, but the order of writable values must not be changed
until this ability is added to the writer.)
Mask : [BinaryData tags only] Bitmask for this value. (Multiple tags
may have the same index by using floating point indices. An
unknown tag will only be generated for a certain TagID if
there is no integral TagID for that tag.) The Mask and
BitShift are applied before evaluating RawConv.
BitShift : [Mask tags only] Bit shift for Mask-ed values. If not
specified, set to the number of trailing bits in the Mask.
When reading, the value is shifted by this number of bits
after the Mask is applied.
Condition : If given, specifies scalar which is evaluated as a Perl
expression at extraction time to decide whether the tag is
valid. If used in a list of alternate tag definitions, the
first list entry with a true condition is taken. If no
condition exists, then a 'true' condition is assumed. The
expression may use $self to access the ExifTool object. The
first 128 bytes of the raw data value are accessible through
the reference $valPt for EXIF, Jpeg2000, QuickTime and
BinaryData tags only (note that for BinaryData tags, the raw
data of $$valPt is always 'undef' type, and may not be used
when writing except for SubDirectory tags). EXIF tags (and
maybe some other types) may also reference the format string
and value count through $format and $count. Note that if the
value is writable and $valPt is used, the tag must have a
Format (unless 'undef' or 'string'), and a Count (unless 1 or
length of the 'undef' or 'string'), so the raw data may be
generated for evaluating the Condition. When writing, $valPt,
$format and $count refer to the new value, except for
MakerNotes tags where $format and $count refer to the old tag
if it existed.
Require : [Composite tags only] A hash reference specifying the tags
required to calculate the Composite tag value. The hash
values are the names of the required tags, and the keys
specify the indices where the tag values are stored in the
@val list used in the ValueConv and/or PrintConv expression.
The Composite value is only calculated if the values for all
Require'd tags are defined. Require, Desire and Inhibit tag
names may be prefixed by an optional group family 0 or 1 name
followed by a colon. Case IS significant. The keys used by
the Require, Desire and Inhibit hashes must not overlap (since
they are used as indices into the common @val, @prt and @raw
lists), and together the keys must be sequential starting from
0. A special feature allows a scalar tag name to be used
instead of the hash reference when only the 0th tag is
defined. For example, the following two definitions are
equivalent:
Require => { 0 => 'XMP:Title' },
Require => 'XMP:Title',
Desire : [Composite tags only] This is the same as Require except that
the Composite value is calculated even if the specified tags
don't exist. Beware that the elements of @val, @prt and @raw
may be undefined for Desire'd tags. If no tags are Require'd,
at least one of the Desire'd tags must exist for the Composite
tag to be generated. If there are no Require'd or Desire'd
tags, then the Composite tag is always generated.
Inhibit : [Composite tags only] Similar to the Require and Desire
hashes, except that the Composite tag is NOT built if any of
the Inhibit tags exist.
Shift : [Writable tags only] Specifies type of shift to apply if this
value may be shifted. Set to 'Time' for shifting date/time
tags, or '0' to prevent tag from being shifted or
conditionally deleted.
Writable : Indicates this tag can be written (or not written if Writable
is set to zero), and for EXIF-type tables gives format for
writing. Writable may be set to 1 for MakerNotes information
because the existing format is always used, however providing
a format is desireable because it is used in validating the
value. For EXIF tables, the Writable flag may be different
than the Format flag, in which case Format is used for
converting the binary value and Writable specifies the format
code written to the EXIF IFD. For SubDirectories in EXIF
information, this flag is only defined if the SubDirectory is
writable as a block, or if the SubDirectory can not be edited
(in which case Writable is set to 0). If non-zero, the
SubDirectory is also extracted as a block, so the Binary and
Protected flags should usually set as well. There is
currently no way to specify a write format for a SubDirectory
that is not writable as a block (the default is 'int32u' for
IFD-type SubDirectories, and 'undef' for all others).
WriteAlso : Used for writable tag to specify other tags to write when this
tag is written. The value is a hash reference. The hash keys
are the names of the tags to write, and the values are
evaluated to obtain the ValueConv values of each tag (or undef
to delete the tag). In the eval, $val is the Raw value of the
parent tag (which may be undef if the tag is being deleted,
and should not be modified because it will affect subsequent
WriteAlso tags), and the %opts hash may be accessed to modify
SetNewValue options for each tag. By default, Type is set to
"ValueConv" and the Protected option has bit 0x02 set to allow
writing of Protected tags that aren't directly writable. The
AddValue, DelValue, Shift and Replace options from the parent
tag are also defined, but no other options are set by default.
Previous new values of WriteAlso tags have already been
removed prior to the eval if the Replace option was used for
the parent tag. If an empty warning is issued ("\n"), the
target tag is not written and no error is reported.
WriteCheck : If given, specifies a scalar which is evaluated as a Perl
expression for a one-time validatation the Raw value being
written. The expression has access to 3 variables: $val is
the value to be written, $self is the ExifTool object, and
$tagInfo is the tag information hash reference. It returns an
error string, or undef if the value is good. If the error
string is empty, the tag is not written and no warnings are
issued, but WriteAlso is still evaluated if it exists.
WriteOnly : Flag set if tag is write-only. Used for documentation only.
DelCheck : Similar to WriteCheck, but called when the tag is deleted. The
expression may access $self, $tagInfo and $wantGroup. Returns
error string, or undef on success, and may set $val to
something other than undef. May return empty string ('') to
suppress warning messages but not delete tag (eg. when
deleting only associated tags).
WriteCondition: [Writable EXIF tags only] Specifies a condition to be
evaluated before the tag can be written to a specific file.
The condition may use $self to reference the ExifTool object,
and returns true if it is OK for writing. Unlike WriteCheck
which is done only once when the new value is set, this
condition is evaluated just before the tag is written to the
file.
WriteGroup : [Writable EXIF and Composite tags only] Specifies the IFD
where the information gets written by default. Must be
defined for writable EXIF tags if WRITE_GROUP is not specified
in table. A WriteGroup of 'All' is special: For writable
Composite tags this causes any group specified for the
Composite tag to be propagated to the WriteAlso tags when
writing. For other tags this allows writing to all EXIF IFD's
simultaneously (in which case the tag should have a Condition
or WriteCondition to restrict the IFD's to which the tag is
actually written).
IsOverwriting : [Writable EXIF tags only] Specifies reference to subroutine
which determines if tag should be overwritten. Arguments are:
0) ExifTool object ref, 1) new value hash ref, 2) old value,
3) new value reference.
Override : [User-defined Composite tags only] Flag to specify that the
new tag definition should override the definition of existing
Composite tags with the same name. Default is 1 unless
otherwise specified.
AllowGroup : [Writable tags only] Regular expression string (case
insensitive) to match group names which are allowed when
writing this tag. Only needed if tag can be written to
groups other than the normal groups for this tag (very rare).
OffsetPair : Used in EXIF table to specify the tagID for the corresponding
offset or length tag.
DataTag : Used in EXIF table to specify the tag name of the data
associated with offset/length tags.
FixFormat : [Writable EXIF SubIFD SubDirectory's only] Used to specify a
format for writing an IFD pointer other than 'int32u'.
ChangeBase : [EXIF tags in JPEG images only] Eval used to return new base
for the offset for this tag only. Eval may use $dirStart and
$dataPos. Note this is geared to the quirky Leica preview
image offset, and is only used if the preview is outside the
APP1 EXIF segment.
BitsPerWord : [BITMASK tags only] Number of bits per decoded word. Defaults
to 32 if not specified.
BitsTotal : [Writable BITMASK tags only] Total number of bits in bit mask.
Defaults to BitsPerWord if not specified.
FixedSize : [EXIF only] Hack to ignore value size and use this instead.
Only valid if Format is also defined.
Struct : [XMP tags only] Reference to structure hash for structured XMP
tags. See "STRUCTURES" section below for more details. (For
backward compatibility, this may be a name to an entry in
%Image::ExifTool::UserDefined::xmpStruct, but this use is
deprecated.) Flattened tags are automatically generated for
each field in the structure. Note that Struct tags can NOT
have ValueConv/PrintConv entries, because values that are HASH
references are are also used by Composite tags, which use the
the Conv entries to generate the Composite value.
NoSubStruct : [XMP tags only] Flag set in flattened tag to break cyclical
recursion in nested structures.
Namespace : [XMP tags only] Gives standard XMP namespace prefix to use for
this tag. If not defined, the tag table NAMESPACE is used.
FlatName : [Struct tags and structure fields only] Name used for
automatically-generated flattened tag names, defaults to Name
if not specified. In general, this is used to remove the
redundant names found in some specifications. May be empty
('') for a Struct tag but not for a structure field.
Units : [MIE tags only] Reference to a list of valid units strings.
The default units are the first item in the list.
Hook : [BinaryData tags only] Expression to be evaluated when
extracting tag to allow dynamic Format, etc for BinaryData
tags. May access $self, and $size (the full size of the
binary data block), and assign a new value to $format to
dynamically set the tag format, and/or increment $varSize to
add a byte offset to subsequent tags. $varSize may be set to
a large number to effectively abort processing of the
directory after this tag. Must have corresponding DATAMEMBER
entry in writable tables. Must not have Unknown set.
LargeTag : [BinaryData tags only] Flag to indicate that the data for this
tag is large, and that it shouldn't be stored in the %val
hash, even if the tag exists as a DATAMEMBER.
SetBase : [QuickTime and BinaryData tags only] Sets ExifTool BASE offset
for use when ExtractInfo is called with the ReEntry flag from
inside the RawConv of a tag.
TagID : [reserved] Used internally to save the table key for this tag.
Note: For XMP tables this corresponds to the XMP property
name, but the table key may have a full XMP namespace prefix
added.
NewTagID : [reserved] Used internally to save new ID of tag in Composite
table if it is different that the original TagID (happens if
there was a conflict with an existing entry in the table)
Index : [reserved] Used internally to save the index of tagInfo items
which are in a conditional list.
Table : [reserved] Reference to parent tag table.
PropertyPath : [reserved] Used internally by XMP writer to save property path
name. Also used in structure field information hashes, but
for these the full property path is not stored.
SrcTagInfo : [reserved] Used internally to store reference to default
language tagInfo hash for alternate-language tags.
OtherLang : [reserved] Used internally by QuickTime module to store a list
of tag ID's for alternate-language tags based on this one.
RootTagInfo : [reserved] Used internally to store a reference to the tag
information hash of the top-level structure for flattened
structure tags.
Module : [reserved] Used internally to store module name for writable
Composite tags.
LangCode : [reserved] Used internally to indicate language code for
alternate language tags (eg. 'fr'). Only used with formats
which support alternate languages (eg. XMP, MIE, etc).
SubDirectory { If it exists, this specifies the start of a new subdirectory.
It contains a collection of variables which specify the type
and location of the subdirectory. Note that ValueConv and
PrintConv do not apply to SubDirectory tags, but RawConv is
evaluated before the SubDirectory is processed. The following
is a list of SubDirectory variables:
TagTable : Specifies the name of the tag table lookup for the new
subdirectory. If not specified, the parent tag table is used.
Start : The offset to the start of the subdirectory relative to the
current Base. This is a Perl expression which may use
$valuePtr to represent the location of the tag value in the
file, or $val for the value itself. If not specified, a Start
of '$valuePtr' is assumed.
OffsetPt : [EXIF directories only] If specified, this is a Perl
expression that gives the position of a 32-bit word in the
current directory that is added to the Start position to get
the position of the new subdirectory. The expression
should use the position of the current tag ($valuePtr).
Base : This expression specifies the base offset for all pointers in
the subdirectory. This need not be specified if the offset is
the same as the current directory, which is normally the case.
May use $start to represent the subdirectory start location
relative to the current base, and $base for the value of the
current base. If this is defined, the automatic validation of
base offsets is disabled for maker notes directories. The IFD
is flagged as using relative offsets when writing if '$start'
is used in this expression.
EntryBased : [EXIF directories only] Flag indicating that the offsets are
based on the individual directory entry position, so offsets
are incremented by 12 times the corresponding entry index.
MaxSubdirs : Maximum number of subdirectories specified by the current tag
(if the tag specifies multiple values). If not specified, the
tag value ($val) is used as-is. If MaxSubdirs is specified,
then one subdirectory is parsed for each value found up to the
maximum number specified. Ignored when writing.
ByteOrder : Specifies byte ordering if different than than the rest of the
file. Must be either BigEndian, LittleEndian or Unknown. If
Unknown is specified, the byte order will be determined from
the directory count (however, this can not be done if OffsetPt
is specified).
Validate : If given, specifies Perl expression which is used to validate
the subdirectory data (regardless of Validate option setting).
The following variables may be used in the expression: $val
(value of the tag), $dirData (reference to directory data),
$subdirStart (offset to subdirectory start) and $size (size of
subdirectory). Returns true if subirectory is valid.
ProcessProc: If given, specifies processing procedure used to decode this
subdirectory data. This overrides the default procedure
specified by PROCESS_PROC in the tag table.
WriteProc : If given, specifies processing procedure used to write this
subdirectory data. This overrides the default procedure
specified by WRITE_PROC in the tag table.
DirName : Name of this subdirectory. If not specified, the name is
taken from the tag name. DirName is important because it is
used when writing to compare against names in the directory
map to determine which directories need to be edited.
FixBase : Flag set if base offsets should be fixed. Used to add a
constant to maker notes offsets to fix damage done by some
image editing utilities. (maker notes only) Set to 2 for
unknown maker notes to be a bit more flexible in adjusting
the base offset.
AutoFix : Flag set to patch GE makernote offset quirks and apply FixBase
without warnings when writing.
FixOffsets : Expression to evaluate for each value pointer to patch
problems with some EXIF maker note offsets. May access the
following variables: $valuePtr, $valEnd, $size, $tagID and
$wFlag. May return undef when writing to ignore the entry.
RelativeBase:[EXIF directories only] Flag to adjust all offsets relative
to the start of the IFD when writing.
Multi : [EXIF directories only] Flag to allow multiple linked IFD's.
1 is assumed if DirName is IFD0 or SubIFD unless otherwise
defined.
Magic : [TiffIFD directories only] Magic number used in TIFF-like
header.
}
STRUCTURES
Structure hashes are very similar to tag tables in that their keys are structure
field ID's and their values are structure field information hashes. The special
keys in structure hashes are:
NAMESPACE : Same as in tag tables, but may be set to undef for a
variable-namespace structure which holds any top-level tag. This
is mandatory for built-in tags, but optional for user-defined
tags (where it defaults to the NAMESPACE of the tag table).
STRUCT_NAME : Name of structure (used in warning messages and documentation).
May contain leading module name separated by a space to avoid
name conflicts with same-named structures in other modules.
Default module is "XMP" unless otherwise specified.
TYPE : rdf:type resource for structure.
NOTES : Notes for documentation.
GROUPS : Same as in tag table, but only the family 2 group name is used,
as the default for the flattened tags.
The contained structure field information hashes are similar to tag information
hashes, except that only the following elements are used:
Raw/Value/PrintConv (and their inverses), TagID (optional), Groups, List,
Writable, Struct, Namespace, LangCode, PropertyPath, Notes.
But note that for PropertyPath, only the element of the path corresponding to
the specific field is stored (including any necessary list properties). The
full property path is obtained by walking the structure tree.
Flattened tags corresponding to each field in a structure are automatically
generated (using an on-demand approach to reduce startup overhead). Pre-defined
flattened tags are allowed, and are used when it is necessary to change the Name
or Description of a flattened tag. The flattened tag information hash entries
are copied from the corresponding structure field definitions, even for
pre-defined flattened tags. The exception is that the List property is
generated automatically unless explicity set to 0 in a pre-defined flattened
tag.
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