Monday, February 13, 2012

PHP: exif_read_data - Fun stuff. I'm going make my own fishing app. I must log and chart.

reject note

Description

array exif_read_data ( string $filename [, string $sections = NULL [, bool $arrays = false [, bool $thumbnail = false ]]] )

exif_read_data() reads the EXIF headers from a JPEG or TIFF 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).

Note:

Windows Me/XP can both wipe the Exif headers when connecting to a camera.

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