-------------------------------------------------------------------------------- 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-eight special keys (TABLE_NAME, SHORT_NAME, PROCESS_PROC, WRITE_PROC, CHECK_PROC, INIT_TABLE, GROUPS, FORMAT, FIRST_ENTRY, TAG_PREFIX, PRINT_CONV, WRITABLE, TABLE_DESC, NOTES, IS_OFFSET, IS_SUBDIR, EXTRACT_UNKNOWN, NAMESPACE, PREFERRED, PERMANENT, 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 NoRefTest - Flag to bypass "referenced by previous directory" test WRITE_PROC : Function reference or name for writing this directory. The function 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 3-4 arguments: 0) ExifTool object reference, 1) tagInfo reference, 2) value reference, and 3) [optional] conversion type. It 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. INIT_TABLE : Routine called to do any necessary initialization before the first time the table is loaded. Argument is a reference to the table. 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 desirable 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. PERMANENT : Tags in this table are Permanent, and can't be deleted. Maker notes tags are Permanent by default, without the need to set this property. 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). Set to 0 for string ID's that look like hex numbers to prevent them from being converted when importing an XML file for language translations in BuildLangModules(). 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. ATOM_COUNT [QuickTime tables only] Maximum number of atoms contained in within this atom. Currently used only for Canon CNTH atom, which contains garbage after the first contained atom. 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, and generated automatically otherwise. 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. 'DelGroup' - set if deleting this tag is the same as deleting the group of the same name. '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. 'NotFlat' - [XMP tags only] Flag indicates that this tag ID does not represent a flattened tag. Used to avoid a conflict if the tag ID would be the same as a generated ID for a flattened tag. The result is that the flattened tag will not be accessible. '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 values in 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. Note that a tag is still writable if it has a RawConv without a RawConvInv (with the exception of QuickTime ItemList and UserData tags, which specifically require this), but this is not true for ValueConv/PrintConv. 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 remaining 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 right 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, in which case the next available index will be used (avoiding collisions with Desire and Inhibit hash entries). 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. A scalar Desire tag name is given the next available index (after scalar Require tags are allocated). 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. A scalar tag name is given the next available index (after scalar Require and Desire tags are allocated). 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 and QuickTime 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 desirable because it is used in validating the value. Set to 2 for tag to show "yes" in the Writable column of the tag name documentation even when there is no WRITE_PROC defined (eg. if it is written via an Extra tag). For EXIF and QuickTime 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 new 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. WriteHook : [QuickTime only] Routine to call with these arguments when tag is encountered during writing: 0) tag value, 1) ExifTool ref. 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. Preferred : This tag is always preferred when writing. 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, $size (the full size of the binary data record), $dataPt (reference to the data block), and $pos (position of this tag in the 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 subdirectory 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, FlatName, 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 explicitly set to 0 in a pre-defined flattened tag. --------------------------------------------------------------------------------