EXIF Data

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EXIF stands for Exchange Image File Format. This is a standard that is set by the Japan Electronic Industry Development Association. This standard is used for storing informational data into an image file. This standard is used in the major image formats used by digital camera manufacturers to allow for interoperability between imaging devices. The full specifications are available at http://www.exif.org.

Most digital cameras use Exif compressed file formats like JPEG. Following the JPEG specification allows for the image data to be read by any software that supports the JPEG format, like web browsers, image editing software and desktop presentation software. In addition to the image, the Exif compressed files also store metadata. This metadata is available to your software and it can be used as a photo log (of sorts) to describe camera settings used in the images that you've taken.

Below is the Exif metadata available from a Nikon Coolpix 995 image as viewed in Image Studio 5 from ArcSoft (free with many Nikon cameras). Please note, this data is not always available to all software products and may not be recorded by all cameras:

Maker=NIKON
Model=E995
Exif Version=0210
Shot Time=2002:07:04 16:02:43
Digitize Time=2002:07:04 16:02:43
Compress Rate=4.0 bits/pixel
Exposure Time=10Second
F Number=2.6
Minimum F Number=
Focal Length=8.20 mm
X Resolution=
Y Resolution=
ISO Speed Rate=ISO100
Flash=No Flash
Light Source=Auto
Exposure Program=Normal
Color space=sRGB
Image Width=2048
Image Length=1536
User Comment=
Related audio file=
Optoelectric conversion factor=
Shutter speed=
Aperture=
Brightness=
Exposure bias=0.00
Maximum lens aperture=0.00
Subject distance=
Metering mode=Pattern
Flash energy=
Spatial frequency response=
Subject location=
Exposure index=
Sensing method=
File source=
Scene type=

As you can see from the information above, not all pieces of information were written by the camera and it follows Exif format 2.1, not the most recent version 2.2. The information available here is important to you if you are going to want to increase your skills as a photographer because it will allow you to not use a notebook to write down every piece of information about every picture that you take. More importantly, it will allow you to get to the point where you can use something other than the 'Auto' functions on your camera.

EXIF Data - Metadata details

On the exif-summary page, you were provided with a high level view of what is available directly from your camera and what is available in most imaging programs. All Exif files (TIFF and JPG) can contain the following TIFF comments.

ARTIST
Person who created the image.
COPYRIGHT
Copyright notice.
DATETIME
Date and time (YYYY:MM:DD HH:MM:SS). The field length is 20, counting the NULL terminator.
DESC
Description of the image.
HOSTCOMP
Computer and operating system in use.
MAKE
Manufacturer of the equipment used to create the image.
MODEL
Model name and number of the equipment.
NAMEOFDOC
Name of the document from which the image was scanned.
NAMEOFPAGE
Page name from which the image was scanned.
SOFTWARE
Name and version of software package used to create the image.

General Exif comments: Exif files can contain the following general comments.


EXIFVERSION
Exif version.
SUBSECTIME
Decimal extension for seconds that are specified in the SZDATETIME field.
DATETIMEORIGINAL
Date and time the original image is captured. The format is YYYY:MM:DD HH:MM:SS. The time is in a 24-hour format, and a blank space is left between the date and the time.
SUBSECTIMEORIGINAL
Decimal extension for seconds that are specified in the SZDATETIMEORIGINAL field.
DATETIMEDIGITIZED
Date and time the file is generated. If the file is generated directly, as with a digital camera, this is the same as the time the original image is captured.
SUBSECTIMEDIGITIZED
Decimal extension for seconds that are specified in the SZDATETIMEDIGITIZED field.
SHUTTERSPEEDVALUE
Shutter speed. The unit of measure is APEX.
APERTURE
Aperture value. This is the ratio of lens aperture for the focal length.
BRIGHTNESS
Brightness value.
EXPOSUREBIAS
Exposure bias. This is the value for correcting a biased exposure.
MAXAPERTURE
Minimum lens f-number.
SUBJECTDISTANCE
Distance from lens to subject (in meters).
METERINGMODE
Photometry mode. Possible values are 0 = Unidentified 1 = Average 2 = Center Weighted Average 3 = Spot 4 = MultiSpot 5 = Pattern 6 = Partial 255 = Others
LIGHTSOURCE
Light source. Possible values are 0 = Unidentified 1 = Daylight 2 = Florescence light 3 = Tungsten Lamp 17 = Standard light source A 18 = Standard light source B 19 = Standard light source C 20 = D55 21 = D65 22 = D75 255 = Others
FLASH
Flash On/Off.
FOCALLENGTH
Focal length, measured in millimeters.
EXPOSURETIME
Exposure time, expressed as a fraction of a second.
FNUMBER
The actual lens F stop (ratio of lens aperture to focal length).
MAKERNOTE
Maker note. The creator of the file determines the data format.
USERCOMMENT
User comment.
SUPPORTEDFLASHPIXVERSION
Supported FlashPix version (Exif 2.0).
COLORSPACE
Color space (Exif 2.0). Specifies whether the color is calibrated or not.
EXPOSUREPROGRAM
Exposure program (Exif 2.0) The class of the program used by the camera to set exposure when the picture is taken. Possible values are: 0 = Not defined 1 = Manual 2 = Aperture priority 4 = Shutter priority 5 = Creative program (biased toward depth of field) 6 = Action program (biased toward fast shutter speed) 7 = Portrait mode (for closeup photos with the background out of focus) Other = reserved
SPECTRALSENSITIVITY
Spectral sensitivity (Exif) - The spectral sensitivity of each channel of the camera used.
ISOSPEEDRATINGS
ISO speed ratings (Exif) - the ISO speed and the ISO Latitude of the camera or input device as specified in ISO 12232
OPTOELECTRICCOEFFICIENT
Optoelectric coefficient (Exif) - Opto-Electric Conversion function specified in ISO 14524. OECF is the relationship between the camera optical input and the image values.
RELATEDSOUNDFILE
Related audio file (Exif) - the name of an audio file related to the image data. The name should be 8 ASCII chars + '.' + 3 chars for extension + NULL.
FLASHENERGY
Flash energy (Exif) - the strobe energy at the time the image iscaptured, as measured in Beam Candle Power Seconds (BPCS)
SPATIALFREQUENCYRESPONSE
Spatial frequency response (Exif) - the camera or input device spatial frequency table and SFR values in the direction of image width, image height and diagonal direction, as specified in ISO 12233.
FOCALPLANEXRESOLUTION
Focal plane X Resolution (Exif) - the number of dots per inch on the camera focal plane in the image width (X) direction
FOCALPLANEYRESOLUTION
Focal plane Y Resolution (Exif) - the number of dots per inch on the camera focal plane in the image height (Y) direction
SUBJECTLOCATION
Subject location (Exif) - the location of the main subject in the scene.
EXPOSUREINDEX
Exposure index (Exif) - the image sensor type on the camera or input device.
SENSINGMETHOD
Sensing method (Exif) - the image sensor type on the camera or input device. Possible values are: 1 = not defined 2 = one-chip color area sensor 3 = two-chip color area sensor 4 = three-chip color area sensor 5 = color sequential area sensor 7 = trilinear sensor 8 = color sequential sensor other = reserved
FILESOURCE
File source (Exif) - the image source. If a digital camera recorded the image, the value will always be 3, to indicate that the image was recorded on a digital camera. Possible values are: 3 = image recorded on a DSC (Digital Still Camera) other = reserved
SCENETYPE
Scene type (Exif) - the type of scene. If a DSC recorded the image, this value will always be 1, indicating that the image was directly photographed. Possible values are: 1 = a directly photographed image other = reserved
CFAPATTERN
CFA Pattern (Exif) - the color filter array (CFA) geometric pattern of the image sensor when a one-chip color sensor was applied. It does not apply to any other sensing methods.

Exif GPS comments. I've actually never seen these pieces of metadata in action, but they are available according to the Exif specification. Exif files can contain the following GPS (Global Positioning System) comments:


GPSVERSIONID
Version number of the GPS image file directory (IFD). The current version is 2.0.0.0. This comment must be included when any GPS comments are used. Unlike the CMNT_EXIFVERSION comment, this comment is written in bytes. A version written as 2.0.0.0 is actually 0x02000000 when coded.
GPSLATITUDEREF
North or south latitude. Possible values are "N" for north and "S" for south.
GPSLATITUDE
Latitude, expressed as three RATIONAL values. When expressed in degrees, minutes, and seconds, latitude is written as dd/1,mm/1,ss/1. If degrees and minutes are used as the units, and minutes are written with fractions to two decimal places, then latitude is expressed as dd/1,mmmm/100,0/1.
GPSLONGITUDEREF
East or west longitude. Possible values are "E" for east and "W" for west.
GPSLONGITUDE
The longitude, expressed as three RATIONAL values. When expressed in degrees, minutes and seconds, longitude is written as ddd/1,mm/1,ss/1. If degrees and minutes are used as the units, and minutes are written with fractions to two decimal places, then longitude is expressed as dd/1,mmmm/100,0/1.
GPSALTITUDEREF
Reference altitude. In the current version, sea level is used as the reference, which must be zero. The reference unit is meters.
GPSALTITUDE
Altitude, in meters, relative to the reference altitude.
GPSTIMESTAMP
Time stamp in UTC (Coordinated Universal Time) time. The time is expressed as three RATIONAL values, for hours, minutes, and seconds.
GPSSATELLITES
GPS satellites used for measurement. The coding format is not stipulated. This comment can be used to code information such as the number of satellites, the satellite number, the satellite's angle of elevation, its azimuth, and its SNR. If the GPS receiver cannot make a measurement, this comment is NULL.
GPSSTATUS
Status of the GPS receiver at when the image is recorded. Possible values are "A" when measurement in progress and "V" when measurement is interrupted.
GPSMEASUREMODE
GPS measurement mode. A value of "2" denotes two-dimensional measurement, and "3" denotes three-dimensional measurement.
GPSDOP
DOP (data precision) value. This comment is an HDOP value during two-dimensional measurement and a PDOP value during three-dimensional measurement.
GPSSPEEDREF
Unit for measuring speed. Possible values are "K" for kilometers, "M" for miles, and "N" for knots.
GPSSPEED
Speed of the GPS receiver.
GPSTRACKREF
Reference for direction of movement. Possible values are "T" for a true direction and "M" for a magnetic.
GPSTRACK
Direction of GPS receiver movement. The range of values is 0.00 to 359.00.
GPSIMGDIRECTIONREF
Reference for the direction of photography in the recorded image. Possible values are "T" for a true direction and "M" for a magnetic.
GPSIMGDIRECTION
Direction of photography in the recorded image. The range of values is 0.00 to 359.00.
GPSMAPDATUM
Geodetic survey data used by the receiver. If the geodetic survey data is restricted to Japan, this tag value is "TOKYO" or "WGS-84".
GPSDESTLATITUDEREF
North or south latitude for the destination point. Possible values are "N" for north and "S" for south.
GPSDESTLATITUDE
Latitude of the destination point. The latitude is expressed as three RATIONAL values, indicating degrees, minutes and seconds.
GPSDESTLONGITUDERE
East or west longitude for the destination point. Possible values are "E" for east and "W" for west.
GPSDESTLONGITUDE
Longitude of the destination point. The longitude is expressed as three RATIONAL values, indicating degrees, minutes and seconds.
GPSDESTBEARINGREF
Reference for the bearing to the destination point. Possible values are "T" for a true direction and "M" for a magnetic.
GPSDESTBEARING
Bearing to the destination point. The range of values is 0.00 to 359.00.
GPSDESTDISTANCEREF
Unit for measuring distance to the destination point. Possible values are "K" for kilometers, "M" for miles, and "N" for nautical miles.
GPSDESTDISTANCE
Distance to the destination point.
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