Features

  1) Extensible (can incorporate user-defined information).
  2) Meaningful tag ID's (hint to meaning of unknown information).
  3) Sequential read/write ability (streamable).
  4) Hierarchical information structure.
  5) Easy to implement reader/writer/editor.
  6) Order of information well defined.
  7) Large data lengths supported: >64kB (+5) and >4GB (+5).
  8) Localized text strings.
  9) Multiple documents in a single file.
 10) Compact format doesn't squander disk space or bandwidth.
 11) Compressed meta information supported.
 12) Relocatable data elements (ie. no fixed offsets).
 13) Binary meta information (+7) with variable byte order (+3).
 14) Mandatory tags not required (an unnecessary complication).
 15) Append information to end of file without editing.

                          Feature number                   Total
     Format  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15   Score
     ------ ---------------------------------------------  -----
     MIE    10 10 10 10 10 10 10 10 10 10 10 10 10 10 10    150
     PDF    10 10  0 10  0  0 10  0 10 10 10  0  7 10 10     97
     PNG    10 10 10  0  8  0  5 10  0 10 10 10  0 10  0     93
     XMP    10 10 10 10  2  0 10 10 10  0  0 10  0 10  0     92
     AIFF    0  5 10 10 10  0  5  0  0 10  0 10  7 10  0     77
     RIFF    0  5 10 10 10  0  5  0  0 10  0 10  7 10  0     77
     JPEG   10  0 10  0 10  0  0  0  0 10  0 10  7 10  0     67
     EPS    10 10 10  0  0  0 10  0 10  0  0  5  0 10  0     65
     CIFF    0  0  0 10 10  0  5  0  0 10  0 10 10 10  0     65
     TIFF    0  0  0 10  5 10  5  0 10 10  0  0 10  0  0     60
     EXIF    0  0  0 10  5 10  0  0  0 10  0  0 10  0  0     45
     IPTC    0  0 10  0  8  0  0  0  0 10  0 10  7  0  0     45

By design, MIE ranks highest by a significant margin. Other formats with reasonable scores are PDF, PNG and XMP, but each has significant weak points. What may be surprising is that TIFF, EXIF and IPTC rank so low.

As well as scoring high in all these features, the MIE format has the unique ability to encapsulate any other type of file, and provides a non-invasive method of adding meta information to a file. The meta information is logically separated from the original file data, which is extremely important because meta information is routinely lost when files are edited.

Also, the MIE format supports multiple files by simple concatenation, enabling all kinds of wonderful features such as linear databases, edit histories or non-intrusive file updates. This ability can also be leveraged to allow MIE-format trailers to be added to some other file types.

File Structure

File Signature

    Byte Number:      0    1    2    3    4    5    6    7

    C Characters:     ~ \x10 \x04    ?    0    M    I    E
        or            ~ \x18 \x04    ?    0    M    I    E

    Hexadecimal:     7e   10   04    ?   30   4d   49   45
        or           7e   18   04    ?   30   4d   49   45

    Decimal:        126   16    4    ?   48   77   73   69
        or          126   24    4    ?   48   77   73   69

Note that byte 1 may have one of the two possible values (0x10 or 0x18), and byte 3 may have any value (0x00 to 0xff).

Element Structure

    1 byte  SyncByte = 0x7e (decimal 126, character '~')
    1 byte  FormatCode (see below)
    1 byte  TagLength (T)
    1 byte  DataLength (gives D if DataLength < 253)
    T bytes TagName (T given by TagLength)
    2 bytes DataLength2 [exists only if DataLength == 255 (0xff)]
    4 bytes DataLength4 [exists only if DataLength == 254 (0xfe)]
    8 bytes DataLength8 [exists only if DataLength == 253 (0xfd)]
    D bytes DataBlock (D given by DataLength)

The minimum element length is 4 bytes (for a group terminator). The maximum DataBlock size is 2^64-1 bytes. TagLength and DataLength are unsigned integers, and the byte ordering for multi-byte DataLength fields is specified by the containing MIE group element. The SyncByte is byte aligned, so no padding is added to align on an N-byte boundary.

FormatCode

The format code is a bitmask that defines the format of the data:

    7654 3210
    ++++ ----  FormatType
    ---- +---  TypeModifier
    ---- -+--  Compressed
    ---- --++  FormatSize

FormatType (bitmask 0xf0):

    0x00 - other (or unknown) data
    0x10 - MIE group
    0x20 - text string
    0x30 - list of null-separated text strings
    0x40 - integer
    0x50 - rational
    0x60 - fixed point
    0x70 - floating point
    0x80 - free space
    

TypeModifier (bitmask 0x08):

Modifies the meaning of certain FormatTypes (0x00-0x60):

    0x08 - other data sensitive to MIE group byte order
    0x18 - MIE group with little-endian byte ordering
    0x28 - UTF encoded text string
    0x38 - UTF encoded text string list
    0x48 - signed integer
    0x58 - signed rational (denominator is always unsigned)
    0x68 - signed fixed-point
    

Compressed (bitmask 0x04):

If this bit is set, the data block is compressed using Zlib deflate. An entire MIE group may be compressed, with the exception of file-level groups.

FormatSize (bitmask 0x03):

Gives the byte size of each data element:

    0x00 - 8 bits  (1 byte)
    0x01 - 16 bits (2 bytes)
    0x02 - 32 bits (4 bytes)
    0x03 - 64 bits (8 bytes)
    

The number of bytes in a single value for this format is given by 2**FormatSize (or 1 << FormatSize). The number of values is the data length divided by this number of bytes. It is an error if the data length is not an even multiple of the format size in bytes.

The following is a list of all currently defined MIE FormatCode values for uncompressed data (add 0x04 to each value for compressed data):

    0x00 - other data (insensitive to MIE group byte order) (1)
    0x01 - other 16-bit data (may be byte swapped)
    0x02 - other 32-bit data (may be byte swapped)
    0x03 - other 64-bit data (may be byte swapped)
    0x08 - other data (sensitive to MIE group byte order) (1)
    0x10 - MIE group with big-endian values (1)
    0x18 - MIE group with little-endian values (1)
    0x20 - ASCII (ISO 8859-1) string (2,3)
    0x28 - UTF-8 string (2,3,4)
    0x29 - UTF-16 string (2,3,4)
    0x2a - UTF-32 string (2,3,4)
    0x30 - ASCII (ISO 8859-1) string list (3,5)
    0x38 - UTF-8 string list (3,4,5)
    0x39 - UTF-16 string list (3,4,5)
    0x3a - UTF-32 string list (3,4,5)
    0x40 - unsigned 8-bit integer
    0x41 - unsigned 16-bit integer
    0x42 - unsigned 32-bit integer
    0x43 - unsigned 64-bit integer (6)
    0x48 - signed 8-bit integer
    0x49 - signed 16-bit integer
    0x4a - signed 32-bit integer
    0x4b - signed 64-bit integer (6)
    0x52 - unsigned 32-bit rational (16-bit numerator then denominator) (7)
    0x53 - unsigned 64-bit rational (32-bit numerator then denominator) (7)
    0x5a - signed 32-bit rational (denominator is unsigned) (7)
    0x5b - signed 64-bit rational (denominator is unsigned) (7)
    0x61 - unsigned 16-bit fixed-point (high 8 bits is integer part) (8)
    0x62 - unsigned 32-bit fixed-point (high 16 bits is integer part) (8)
    0x69 - signed 16-bit fixed-point (high 8 bits is signed integer) (8)
    0x6a - signed 32-bit fixed-point (high 16 bits is signed integer) (8)
    0x72 - 32-bit IEEE float (not recommended for portability reasons)
    0x73 - 64-bit IEEE double (not recommended for portability reasons) (6)
    0x80 - free space (value data does not contain useful information)

Notes:

1.

The byte ordering specified by the MIE group TypeModifier applies to the MIE group element as well as all elements within the group. Data for all FormatCodes except 0x08 (other data, sensitive to byte order) may be transferred between MIE groups with different byte order by byte swapping the uncompressed data according to the specified data format. The following list illustrates the byte-swapping pattern, based on FormatSize, for all format types except rational (FormatType 0x50).

      FormatSize              Change in Byte Sequence
    --------------      -----------------------------------
    0x00 (8 bits)       0 1 2 3 4 5 6 7 --> 0 1 2 3 4 5 6 7 (no change)
    0x01 (16 bits)      0 1 2 3 4 5 6 7 --> 1 0 3 2 5 4 7 6
    0x02 (32 bits)      0 1 2 3 4 5 6 7 --> 3 2 1 0 7 6 5 4
    0x03 (64 bits)      0 1 2 3 4 5 6 7 --> 7 6 5 4 3 2 1 0
    

Rational values consist of two integers, so they are swapped as the next lower FormatSize. For example, a 32-bit rational (FormatSize 0x02, and FormatCode 0x52 or 0x5a) is swapped as two 16-bit values (ie. as if it had FormatSize 0x01).

2.

The TagName of a string element may have an 6-character suffix to indicate a specific locale. (eg. "Title-en_US", or "Keywords-de_DE").

3.

Text strings are not normally null terminated, however they may be padded with one or more null characters to the end of the data block to allow strings to be edited within fixed-length data blocks. Newlines in the text are indicated by a single LF (0x0a) character.

4.

UTF strings must not begin with a byte order mark (BOM) since the byte order and byte size are specified by the MIE format. If a BOM is found, it should be treated as a zero-width non-breaking space.

5.

A list of text strings separated by null characters. These lists must not be null padded or null terminated, since this would be interpreted as additional zero-length strings. For ASCII and UTF-8 strings, the null character is a single zero (0x00) byte. For UTF-16 or UTF-32 strings, the null character is 2 or 4 zero bytes respectively.

6.

64-bit integers and doubles are subject to the specified byte ordering for both 32-bit words and bytes within these words. For instance, the high order byte is always the first byte if big-endian, and the eighth byte if little-endian. This means that some swapping is always necessary for these values on systems where the byte order differs from the word order (eg. some ARM systems), regardless of the endian-ness of the stored values.

7.

Rational values are treated as two separate integers. The numerator always comes first regardless of the byte ordering. In a signed rational value, only the numerator is signed. The denominator of all rational values is unsigned (eg. a signed 64-bit rational of 0x80000000/0x80000000 evaluates to -1, not +1).

8.

32-bit fixed point values are converted to floating point by treating them as an integer and dividing by an appropriate value. eg)

    16-bit fixed value = 16-bit integer value / 256.0
    32-bit fixed value = 32-bit integer value / 65536.0
    

TagLength

Gives the length of the TagName string. Any value between 0 and 255 is valid, but the TagLength of 0 is valid only for the MIE group terminator.

DataLength

DataLength is an unsigned byte that gives the number of bytes in the data block. A value between 0 and 252 gives the data length directly, and numbers from 253 to 255 are reserved for extended DataLength codes. Codes of 255, 254 and 253 indicate that the element contains an additional 2, 4 or 8 byte unsigned integer representing the data length.

    0-252      - length of data block
    255 (0xff) - use DataLength2
    254 (0xfe) - use DataLength4
    253 (0xfd) - use DataLength8

A DataLength of zero is valid for any element except a compressed MIE group. A zero DataLength for an uncompressed MIE group indicates that the group length is unknown. For other elements, a zero length indicates there is no associated data. A terminator element must have a DataLength of 0, 6 or 10, and may not use an extended DataLength.

TagName

The TagName string is 0 to 255 bytes long, and is composed of the ASCII characters A-Z, a-z, 0-9 and underline ('_'). Also, a dash ('-') is used to separate the language/country code in the TagName of a localized text string, and a units string (possibly containing other ASCII characters) may be appear in brackets at the end of the TagName. The TagName string is NOT null terminated. A MIE element with a tag string of zero length is reserved for the group terminator.

MIE elements are sorted alphabetically by TagName within each group. Multiple elements with the same TagName are allowed, even within the same group.

TagNames should be meaningful. Case is significant. Words should be lowercase with an uppercase first character, and acronyms should be all upper case. The underline ("_") is provided to allow separation of two acronyms or two numbers, but it shouldn't be used unless necessary. No separation is necessary between an acronym and a word (eg. "ISOSetting").

All TagNames should start with an uppercase letter. An exception to this rule allows tags to begin with a digit (0-9) if they must come before other tags in the sort order, or a lowercase letter (a-z) if they must come after. For instance, the '0Type' element begins with a digit so it comes before, and the 'data' element begins with a lowercase letter so that it comes after meta information tags in the main "0MIE" group.

Tag names for localized text strings have an 6-character suffix with the following format: The first character is a dash ('-'), followed by a 2-character lower case ISO 639-1 language code, then an underline ('_'), and ending with a 2-character upper case ISO 3166-1 alpha 2 country code. (eg. "-en_US", "-en_GB", "-de_DE" or "-fr_FR". Note that "GB", and not "UK" is the code for Great Britain, although "UK" should be recognized for compatibility reasons.) The suffix is included when sorting the tags alphabetically, so the default locale (with no tag-name suffix) always comes first. If the country is unknown or not applicable, a country code of "XX" should be used.

Tags with numerical values may allow units of measurement to be specified. The units string is stored in brackets at the end of the tag name, and is composed of zero or more ASCII characters in the range 0x21 to 0x7d, excluding the bracket characters 0x28 and 0x29. (eg. "Resolution(/cm)" or "SpecificHeat(J/kg.K)".) See Image::ExifTool::MIEUnits for details. Unit strings are not localized, and may not be used in combination with localized text strings.

Sets of tags which would require a common prefix should be added in a separate MIE group instead of adding the prefix to all tag names. For example, instead of these TagName's:

    ExternalFlashType
    ExternalFlashSerialNumber
    ExternalFlashFired

one would instead designate a separate "ExternalFlash" MIE group to contain the following elements:

    Type
    SerialNumber
    Fired

DataLength2/4/8

These extended DataLength fields exist only if DataLength is 255, 254 or 253, and are respectively 2, 4 or 8 byte unsigned integers giving the data block length. One of these values must be used if the data block is larger than 252 bytes, but they may be used if desired for smaller blocks too (although this may add a few unnecessary bytes to the MIE element).

DataBlock

The data value for the MIE element. The format of the data is given by the FormatCode. For MIE group elements, the data includes all contained elements and the group terminator.

MIE groups

A MIE group element is identified by a format code of 0x10 (big endian byte ordering) or 0x18 (little endian). The group terminator is distinguished by a zero TagLength (it is the only element allowed to have a zero TagLength), and has a FormatCode of 0x00.

The MIE group element is permitted to have a zero DataLength only if the data is uncompressed. This special value indicates that the group length is unknown (otherwise the minimum value for DataLength is 4, corresponding the the minimum group size which includes a terminator of at least 4 bytes). If DataLength is zero, all elements in the group must be parsed until the group terminator is found. If non-zero, DataLength includes the length of all elements contained within the group, including the group terminator. Use of a non-zero DataLength is encouraged because it allows readers quickly skip over entire MIE groups. For compressed groups DataLength must be non-zero, and is the length of the compressed group data (which includes the compressed group terminator).

Group Terminator

The group terminator has a FormatCode and TagLength of zero. The terminator DataLength must be 0, 6 or 10 bytes, and extended DataLength codes may not be used. With a zero DataLength, the byte sequence for a terminator is "7e 00 00 00" (hex). With a DataLength of 6 or 10 bytes, the terminator data block contains information about the length and byte ordering of the preceding group. This additional information is recommended for file-level groups, and is used in multi-document MIE files and MIE trailers to allow the file to be scanned backwards from the end. (This may also allow some documents to be recovered if part of the file is corrupted.) The structure of this optional terminator data block is as follows:

    4 or 8 bytes  GroupLength (unsigned integer)
    1 byte        ByteOrder (0x10 or 0x18, same as MIE group)
    1 byte        GroupLengthSize (0x04 or 0x08)

The ByteOrder and GroupLengthSize values give the byte ordering and size of the GroupLength integer. The GroupLength value is the total length of the entire MIE group ending with this terminator, including the opening MIE group element and the terminator itself.

File-level MIE groups

File-level MIE groups may NOT be compressed.

All elements in a MIE file are contained within a special group with a TagName of "0MIE". The purpose of the "OMIE" group is to provide a unique signature at the start of the file, and to encapsulate information allowing files to be easily combined. The "0MIE" group must be terminated like any other group, but it is recommended that the terminator of a file-level group include the optional data block (defined above) to provide information about the group length and byte order.

It is valid to have more than one "0MIE" group at the file level, allowing multiple documents in a single MIE file. Furthermore, the MIE structure enables multi-document files to be generated by simply concatenating two or more MIE files.

Scanning Backwards through a MIE File

1.

Read the last 10 bytes of the file. (Note that a valid MIE file may be as short as 12 bytes long, but a file this length contains only an an empty MIE group.)

2.

If the last byte of the file is zero, then it is not possible to scan backward through the file, so the file must be scanned from the beginning. Otherwise, proceed to the next step.

3.

If the last byte is 4 or 8, the terminator contains information about the byte ordering and length of the group. Otherwise, stop here because this isn't a valid MIE file.

4.

The next-to-last byte must be either 0x10 indicating big-endian byte ordering or 0x18 for little-endian ordering, otherwise this isn't a valid MIE file.

5.

The value of the preceding 4 or 8 bytes gives the length of the complete file-level MIE group (GroupLength). This length includes both the leading MIE group element and the terminator element itself. The value is an unsigned integer with a byte length given in step 3), and a byte order from step 4). From the current file position (at the end of the data read in step 1), seek backward by this number of bytes to find the start of the MIE group element for this document.

This algorithm may be repeated again beginning at this point in the file to locate the next-to-last document, etc.

The table below lists all 5 valid patterns for the last 14 bytes of a file-level MIE group, with all numbers in hex. The comments indicate the length and byte ordering of GroupLength (xx) if available:

  ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 7e 00 00 00  - (no GroupLength)
  ?? ?? ?? ?? 7e 00 00 06 xx xx xx xx 10 04  - 4 bytes, big endian
  ?? ?? ?? ?? 7e 00 00 06 xx xx xx xx 18 04  - 4 bytes, little endian
  7e 00 00 0a xx xx xx xx xx xx xx xx 10 08  - 8 bytes, big endian
  7e 00 00 0a xx xx xx xx xx xx xx xx 18 08  - 8 bytes, little endian

Trailer Signature

  ?? ?? ?? ?? 7e 00 04 00 7a 6d 69 65 7e 00 00 06 xx xx xx xx 10 04
  ?? ?? ?? ?? 7e 00 04 00 7a 6d 69 65 7e 00 00 06 xx xx xx xx 18 04
  7e 00 04 00 7a 6d 69 65 7e 00 00 0a xx xx xx xx xx xx xx xx 10 08
  7e 00 04 00 7a 6d 69 65 7e 00 00 0a xx xx xx xx xx xx xx xx 18 08

Note that the zero-DataLength terminator may not be used here because the trailer length must be known for seeking backwards from the end of the file.

Multiple trailers may be appended to the same file using this technique.

MIE Data Values

It is preferred that closely related values with the same format are written to a single tag instead of using multiple tags. This improves localization of like values and decreases MIE element overhead. For instance, instead of separate ImageWidth and ImageHeight tags, a single ImageSize tag is defined.

Tags which may take on a discrete set of values should have meaningful values if possible. This improves the extensibility of the format and allows a more reasonable interpretation of unrecognized values.

Numerical Representation

Integer and floating point numbers may be represented in binary or string form. In string form, integers are a series of digits with an optional leading sign (eg. "[+|-]DDDDDD"), and multiple values are separated by a single space character (eg. "23 128 -32"). Floating point numbers are similar but may also contain a decimal point and/or a signed exponent with a leading 'e' character (eg. "[+|-]DD[.DDDDDD][e(+|-)EEE]"). The string "inf" is used to represent infinity. One advantage of numerical strings is that they can have an arbitrarily high precision because the possible number of significant digits is virtually unlimited.

Note that numerical values may have associated units of measurement which are specified in the "TagName" string.

Date/Time Format

All MIE dates are strings in the form "YYYY:mm:dd HH:MM:SS.ss+HH:MM". The fractional seconds (".ss") are optional, and if included may contain any number of significant digits (unlike all other fields which are a fixed number of digits and must be padded with leading zeros if necessary). The timezone ("+HH:MM" or "-HH:MM") is recommended but not required. If not given, the local system timezone is assumed.

MIME Type

Levels of Support

Compression

Software not supporting compression must ignore compressed elements and groups, but should be able to process the remaining information.

Large data lengths

Some software may limit the maximum size of a MIE group or element. Historically, a limit of 2GB may be imposed by some systems. However, 8-byte data lengths should be supported by all applications provided the value doesn't exceed the system limit. (eg. For systems with a 2GB limit, 8-byte data lengths should be supported if the upper 17 bits are all zero.) If a data length above the system limit is encountered, it may be necessary for the application to stop processing if it can not seek to the next element in the file.

Encapsulating Information with Data in a MIE File

    exiftool -o new.mie -tagsfromfile FILE '-mie:all<all' \
        '-subfilename<filename' '-subfiletype<filetype' \
        '-subfilemimetype<mimetype' '-subfiledata<=FILE'

where "FILE" is the name of the file.

For unrecognized files, this command may be used:

    exiftool -o new.mie -subfilename=FILE -subfiletype=TYPE \
        -subfilemimetype=MIME '-subfiledata<=FILE'

where "TYPE" and "MIME" represent the source file type and MIME type respectively.

Adding a MIE Trailer to a File

Creating a MIE trailer with ExifTool is a two-step process since ExifTool can't currently be used to add a MIE trailer directly. The example below illustrates the steps for adding a MIE trailer with a small preview image ("small.jpg") to a destination JPEG image ("dst.jpg").

Step 1) Create a MIE file with a TrailerSignature containing the desired information:

    exiftool -o new.mie -trailersignature=1 -tagsfromfile small.jpg \
        '-previewimagetype<filetype' '-previewimagesize<imagesize' \
        '-previewimagename<filename' '-previewimage<=small.jpg'

Step 2) Append the MIE information to another file. In Unix, this can be done with the 'cat' command:

    cat new.mie >> dst.jpg

Once added, ExifTool may be used to edit or delete a MIE trailer in a JPEG or TIFF image.

Multiple MIE Documents in a Single File

    # write the Author tag in the second MIE document
    exiftool -mie2:author=phil test.mie

    # delete the first MIE document from a file
    exiftool -mie1:all= test.mie

Units of Measurement

    exiftool -mie:gpsaltitude='7500(ft)' test.mie

If no units are provided, the default units are written.

Localized Text

    exiftool -comment-en_us='this is a comment' test.mie