exif_read_data() reads the EXIF headers from an image file. This way you can read meta data generated by digital cameras.
EXIF headers tend to be present in JPEG/TIFF images generated by digital cameras, but unfortunately each digital camera maker has a different idea of how to actually tag their images, so you can't always rely on a specific Exif header being present.
Height and Width are computed the same way getimagesize() does so their values must not be part of any header returned. Also, html is a height/width text string to be used inside normal HTML.
When an Exif header contains a Copyright note, this itself can contain two values. As the solution is inconsistent in the Exif 2.10 standard, the COMPUTED section will return both entries Copyright.Photographer and Copyright.Editor while the IFD0 sections contains the byte array with the NULL character that splits both entries. Or just the first entry if the datatype was wrong (normal behaviour of Exif). The COMPUTED will also contain the entry Copyright which is either the original copyright string, or a comma separated list of the photo and editor copyright.
The tag UserComment has the same problem as the Copyright tag. It can store two values. First the encoding used, and second the value itself. If so the IFD section only contains the encoding or a byte array. The COMPUTED section will store both in the entries UserCommentEncoding and UserComment. The entry UserComment is available in both cases so it should be used in preference to the value in IFD0 section.
exif_read_data() also validates EXIF data tags according to the EXIF specification (» http://exif.org/Exif2-2.PDF, page 20).
Windows Me/XP can both wipe the Exif headers when connecting to a camera.
The location of the image file. This can either be a path to the file (stream wrappers are also supported as usual) or a stream resource.
Is a comma separated list of sections that need to be present in file to produce a result array. If none of the requested sections could be found the return value is FALSE.
COMPUTED html, Width, Height, IsColor, and more if available. Height and Width are computed the same way getimagesize() does so their values must not be part of any header returned. Also, html is a height/width text string to be used inside normal HTML.
IFD0 All tagged data of IFD0. In normal imagefiles this contains image size and so forth.
THUMBNAIL A file is supposed to contain a thumbnail if it has a second IFD. All tagged information about the embedded thumbnail is stored in this section.
COMMENT Comment headers of JPEG images.
EXIF The EXIF section is a sub section of IFD0. It contains more detailed information about an image. Most of these entries are digital camera related.
Specifies whether or not each section becomes an array. The sections COMPUTED, THUMBNAIL, and COMMENT always become arrays as they may contain values whose names conflict with other sections.
When set to TRUE the thumbnail itself is read. Otherwise, only the tagged data is read.
It returns an associative array where the array indexes are the header names and the array values are the values associated with those headers. If no data can be returned, exif_read_data() will return FALSE.
7.2.0 The filename parameter was renamed to stream and now supports both local files or stream resources.
4.3.0 Can read all embedded IFD data including arrays (returned as such). Also the size of an embedded thumbnail is returned in a THUMBNAIL subarray, and can return thumbnails in TIFF format. Also, there is no longer a maximum length for returned values (not until the memory limit has been reached).
4.3.0 If the image contains any IFD0 data then COMPUTED contains the entry ByteOrderMotorola which is 0 for little-endian (intel) and 1 for big-endian (motorola) byte order. Also, COMPUTED and UserComment no longer only contain the first copyright entry if the datatype was wrong.
The first call fails because the image has no header information.
If mbstring is enabled, exif will attempt to process the unicode and pick a charset as specified by exif.decode_unicode_motorola and exif.decode_unicode_intel. The exif extension will not attempt to figure out the encoding on its own, and it is up to the user to properly specify the encoding for which to use for decoding by setting one of these two ini directives prior to calling exif_read_data().
If the stream is used to pass a stream to this function, then the stream must be seekable. Note that the file pointer position is not changed after this function returns.