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# XXXIII. Exif Functions

# Introduction

With the exif extension you are able to work with image meta data. For example, you may use exif functions to read meta data of pictures taken from digital cameras by working with information stored in the headers of the JPEG and TIFF images.

# Requirements

Your PHP must be compiled in with --enable-exif. PHP does not require any additional library for the exif module. Windows users must also have the mbstring extension enabled.

# Installation

To enable exif-support configure PHP with --enable-exif

Windows users must enable both the `php_mbstring.dll` and `php_exif.dll` DLL's in `php.ini`. The `php_mbstring.dll` DLL must be loaded before the `php_exif.dll` DLL so adjust your `php.ini` accordingly.

# Runtime Configuration

The behaviour of these functions is affected by settings in `php.ini`.

Exif supports automatically conversion for Unicode and JIS character encodings of user comments when module mbstring is available. This is done by first decoding the comment using the specified characterset. The result is then encoded with another characterset which should match your HTTP output.

Table 1. Exif configuration options

Name | Default | Changeable | Changelog
--- | --- | --- | ---
exif.encode_unicode | "ISO-8859-15" | PHP_INI_ALL | Available since PHP 4.3.0.
exif.decode_unicode_motorola | "UCS-2BE" | PHP_INI_ALL | Available since PHP 4.3.0.
exif.decode_unicode_intel | "UCS-2LE" | PHP_INI_ALL | Available since PHP 4.3.0.
exif.encode_jis | "" | PHP_INI_ALL | Available since PHP 4.3.0.
exif.decode_jis_motorola | "JIS" | PHP_INI_ALL | Available since PHP 4.3.0.
exif.decode_jis_intel | "JIS" | PHP_INI_ALL | Available since PHP 4.3.0.

For further details and definitions of the PHP_INI_* constants, see the Appendix G.

Here's a short explanation of the configuration directives.

exif.encode_unicode string

  exif.encode_unicode defines the characterset UNICODE user comments are handled. This defaults to ISO-8859-15 which should work for most non Asian countries. The setting can be empty or must be an encoding supported by mbstring. If it is empty the current internal encoding of mbstring is used.

exif.decode_unicode_motorola string

  exif.decode_unicode_motorola defines the image internal characterset for Unicode encoded user comments if image is in motorola byte order (big-endian). This setting cannot be empty but you can specify a list of encodings supported by mbstring. The default is UCS-2BE.

exif.decode_unicode_intel string

  exif.decode_unicode_intel defines the image internal characterset for Unicode encoded user comments if image is in intel byte order (little-endian). This setting cannot be empty but you can specify a list of encodings supported by mbstring. The default is UCS-2LE.

exif.encode_jis string

  exif.encode_jis defines the characterset JIS user comments are handled. This defaults to an empty value which forces the functions to use the current internal encoding of mbstring.

exif.decode_jis_motorola string

  exif.decode_jis_motorola defines the image internal characterset for JIS encoded user comments if image is in motorola byte order (big-endian). This setting cannot be empty but you can specify a list of encodings supported by mbstring. The default is JIS.

exif.decode_jis_intel string

  exif.decode_jis_intel defines the image internal characterset for JIS encoded user comments if image is in intel byte order (little-endian). This setting cannot be empty but you can specify a list of encodings supported by mbstring. The default is JIS.

# Resource Types

This extension has no resource types defined.

# Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

`EXIF_USE_MBSTRING` (integer)

The exif_imagetype() lists several related built-in constants.

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