Exchangeable Image File Format - Problems - Technical

Technical

Apart from not being a maintained standard, the Exif format has a number of drawbacks, mostly relating to its use of legacy file structures.

  • The derivation of Exif from the TIFF file structure using offset pointers in the files means that data can be spread anywhere within a file, which means that software is likely to corrupt any pointers or corresponding data that it doesn't decode/encode. For this reason most image editors damage or remove the Exif metadata to some extent upon saving.
  • The standard defines a MakerNote tag, which allows camera manufacturers to place any custom format metadata in the file. This is used increasingly by camera manufacturers to store myriad camera settings not listed in the Exif standard, such as shooting modes, post-processing settings, serial number, focusing modes, etc. As this tag format is proprietary and manufacturer-specific, it can be prohibitively difficult to retrieve this information from an image (or properly preserve it when rewriting an image). Some manufacturers encrypt portions of the information; for example, Nikon encrypts the detailed lens data in their newer MakerNote data versions.
  • The standard only allows TIFF or JPEG files — there is no provision for a "raw" file type which would be a direct data dump from the sensor device. This has caused camera manufacturers to invent many proprietary, incompatible "raw" file formats. To solve this problem, Adobe developed the DNG format (a TIFF-based raw file format), in hopes that manufacturers would standardize on a single, raw file format.
  • The Exif standard specifically states that color depth is always 24 bits. However, many modern cameras, such as the Nikon D70 which captures 36 bits of color per pixel, can capture significantly more. Since Exif/DCF files cannot represent this color depth, many manufacturers have developed proprietary, non-compatible Raw image formats.
  • Some digital cameras can also capture video. The Exif standard has no provision for video files.
  • Exif is very often used in images created by scanners, but the standard makes no provisions for any scanner-specific information.
  • Photo manipulation software sometimes fails to update the embedded thumbnail after an editing operation, possibly causing the user to inadvertently publish compromising information.
  • Exif metadata are restricted in size to 64 kB in JPEG images because according to the specification this information must be contained within a single JPEG APP1 segment. Although the FlashPix extensions allow information to span multiple JPEG APP2 segments, these extensions are not commonly used. This has prompted some camera manufacturers to develop non-standard techniques for storing the large preview images used by some digital cameras for LCD review. These non-standard extensions are commonly lost if a user re-saves the image using image editor software, possibly rendering the image incompatible with the original camera that created it.
  • There is no way to record time-zone information along with the time, thus rendering the stored time ambiguous.
  • There is no field to record readouts of a camera's accelerometers or inertial navigation system. Such data could help to establish the relationship between the image sensor’s XYZ coordinate system and the gravity vector (i.e., which way is down in this image). It could also establish relative camera positions or orientations in a sequence of photos.

Read more about this topic:  Exchangeable Image File Format, Problems

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