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=begin
= ruby-libexif - an interface to libexif library
((<libexif|URL:http://libexif.sourceforge.net>)) is the library for parsing image information contained in EXIF format images. ruby-libexif provides a simple interface to this library.
= Usage
require 'exif'
#
# generate Exif object from 'image.jpg' in the current directory.
#
exif = Exif.new('image.jpg')
#
# generate an empty Exif object, and load the image data into it.
#
exif = Exif.new
File.open('image.jpg') { |f| exif << f.read }
#
# To access the value of the tag, use Exif#[].
# The return value are string object.
# You can specify a tag by its name or title, or ID.
# For example, if you want to know the manufacturer of
# the recording equipment that generated the image,
# you can get the information by specifying the tag as follows:
#
# * exif['Manufacturer'] ; "tag title"
# * exif['Make'] ; "tag name"
# * exif[0x010f] ; "tag ID"
#
(Please refer ((<Exif.[]>)) , ((<Exif#[]>)) for more details, and ((<Exif#list_tags>)) for available tags in the IFD.)
# get a value of the specifid tag by its title
p exif["Manufacturer"] # -> "FUJIFILM"
# get a value of the specified tag by its tag ID (string)
p exif[0xa001] # -> "FUJIFILM"
#
# If the image has thumbnail, you can extract it by
# Exif#extract_thumbnail, or Exif#thumbnail
#
# extract a thumbnail, and save it to a file.
File.open('thumb.jpg', 'wb') {|dest| exif.thumbnail(dest)}
# set a new thumbnail to Exif object. note that existing
# thumbnail, if exists, will be destroyed.
File.open('src.jpg', 'rb'){|src| exif.thumbnail = src.read }
= Reference
== class Exif
=== class methods
--- Exif.new
generate a new Exif object with empty data.
--- Exif.new(fpath)
load the image data from (({fpath})), and generates a new Exif object. If the image is not EXIF-formatted, exception ((<Exif::Error::NotExifFormat>)) raises.
--- Exif.[](tagid)
get a description of ((|tagid|)). the returned value is an array object:
['tag title', ['tag name', 'description of the tag', 'tag ID']]
=== instance methods
--- Exif#data=(str)
--- Exif#<<(str)
set the image data given as String object. The existing data in the object, if exists, will be destroyed.
--- Exif#list_tags(ifd)
return an array consists of tags defiend in IFD ((|ifd|)). each elements is following array object:
["tag title", "tag ID('0xdddd')"]
((|ifd|)) is one of the constants defined in ((<Exif::IFD>)).
--- Exif#byte_order
--- Exif#ifd
return a string that represents current IFD.
--- Exif#ifd=(ifd)
set IFD of the object to ((|ifd|)). ((|ifd|)) is one of the constants defined in ((<Exif::IFD>)), or either one of "0", "1", "GPS", "Interoperability". If invalid IFD is given, exception ((<Exif::Error::InvalidIFD>)) raises.
--- Exif#[](tag)
return the value (string) of the (({tag})). If the tag is not supported by current IFD, exception ((<Exif::Error::TagNotFound>)) raises. Unless you have set IFD by ((<Exif#ifd=>)), this method tries to find the tag and its value over available IFDs.
--- Exif#each_entry(use_tag_id=false) {|tag, val| ...}
executes the block, with the block arguments being tag title ((|tag|)) over the LFDs and its value ((|val|)). If ((|use_tag_id|)) is ((|true|)), ((|tag|)) is set to tag ID (denoted by '0xdddd').
--- Exif#extract_thumbnail(dest)
--- Exif#thumbnail(dest)
write the thumbnail of the image to ((|dest|)), using (({dest#<<})). If the image does not have thumbnail, exception ((<Exif::Error::ThumbnailNotFound>)) raises.
== modules
== Exif::IFD
IFDs defined in libexif.
--- Exif::IFD::Zero
--- Exif::IFD::One
--- Exif::IFD::EXIF
--- Exif::IFD::GPS
--- Exif::IFD::Interoperability
--- Exif::IFD::Any
This constant should be set in ((<Exif#ifd=>)) if ((<Exif#[]>)) searches tag over above five IFDs. Exif object is set to this value by default.
== Exif::ByteOrder
constants that represents byte order of the EXIF image.
--- Exif::ByteOrder::INTEL
--- Exif::ByteOrder::MOTOROLA
== Exception classes
RuntimeError --- Exif::Error -+- Exif::Error::NotExifFormat
|- Exif::Error::InvalidIFD
|- Exif::Error::ThumbnailNotFound
`- Exif::Error::TagNotFound
--- Exif::Error
Runtime errors occurred by using ruby-libexif belong to this class, or following derived classes.
--- Exif::Error::NotExifFormat
--- Exif::Error::InvalidIFD
--- Exif::Error::TagNotFound
--- Exif::Error::ThumbnailNotFound
=end
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