EXIF

EXIF or the Exchangeable Image File Format is a standard produced by the Japan Electronics and Information Technology Industries Association. The standard specifies the formats to be used for images, sound and tags in digital still cameras and in other systems handling the image and sound files recorded by digital still cameras. The data embedded generally relates to the physical attributes of the image (e.g. width, height, whether a flash was used, camera shutter speed, F stop used, etc.) rather than attributes about the subject of the image (e.g. keywords, location, etc.). As such, EXIF metadata is closely tied to the master image as it describes the physical attributes of that image.

EXIF information is embedded in an image using the TIFF 6.0 tags specification. Each EXIF property (that is a setting value, like Flash Fired - indicating whether the flash was used) is described by two numbers. The first number, called the IFD (Image File Directory) represents the broad area within which the property resides. EXIF provides five possible IFDs:

  1. Primary Image IFD (Primary)
  2. EXIF specific IFD (Exif)
  3. GPS (Global Positioning System) IFD (GPS)
  4. Interoperability IFD (Interopability)
  5. Thumbnail IFD (Thumbnail)

Each IFD has its own set of numbers that represent specific attributes within that IFD; each number is known as a tag. For example, the EXIF IFD has a tag number 36867 that contains the date and time the picture was taken. By combining the IFD and the tag we get a unique identifier for a metadata value. The value 2:36867 represents the 2nd IFD (EXIF specific) with tag 36867 (date and time picture was taken). The IFD:Tag notation is used by to specify EXIF metadata values.

The tables below describe the possible tags for each IFD. For a complete description of the values available for a given attribute, please consult the EXIF Version 2.2 standard.

Code

Name

Short description
254 NewSubfileType A general indication of the kind of data contained in this subfile.
255 SubfileType A general indication of the kind of data contained in this subfile.
256 ImageWidth The number of columns in the image, i.e., the number of pixels per row.
257 ImageLength The number of rows of pixels in the image.
258 BitsPerSample Number of bits per component.
259 Compression Compression scheme used on the image data.
262 PhotometricInterpretation The colour space of the image data.
263 Threshholding For black and white TIFF files that represent shades of gray, the technique used to convert from gray to black and white pixels.
264 CellWidth The width of the dithering or halftoning matrix used to create a dithered or halftoned bilevel file.
265 CellLength The length of the dithering or halftoning matrix used to create a dithered or halftoned bilevel file.
266 FillOrder The logical order of bits within a byte.
270 ImageDescription A string that describes the subject of the image.
271 Make The scanner manufacturer.
272 Model The scanner model name or number.
273 StripOffsets For each strip, the byte offset of that strip.
274 Orientation The orientation of the image with respect to the rows and columns.
277 SamplesPerPixel The number of components per pixel.
278 RowsPerStrip The number of rows per strip.
279 StripByteCounts For each strip, the number of bytes in the strip after compression.
280 MinSampleValue The minimum component value used.
281 MaxSampleValue The maximum component value used.
282 XResolution The number of pixels per ResolutionUnit in the ImageWidth direction.
283 YResolution The number of pixels per ResolutionUnit in the ImageLength direction.
284 PlanarConfiguration How the components of each pixel are stored.
288 FreeOffsets For each string of contiguous unused bytes in a TIFF file, the byte offset of the string.
289 FreeByteCounts For each string of contiguous unused bytes in a TIFF file, the number of bytes in the string.
290 GrayResponseUnit The precision of the information contained in the GrayResponseCurve.
291 GrayResponseCurve For grayscale data, the optical density of each possible pixel value.
296 ResolutionUnit The unit of measurement for XResolution and YResolution.
305 Software Name and version number of the software package(s) used to create the image.
306 DateTime Date and time of image creation.
315 Artist Person who created the image.
316 HostComputer The computer and / or operating system in use at the time of image creation.
320 ColorMap A colour map for palette colour images.
338 ExtraSamples Description of extra components.
33432 Copyright Copyright notice.

Code

Name

Short description
33434 ExposureTime Exposure time, given in seconds.
33437 FNumber The F number.
34850 ExposureProgram The class of the program used by the camera to set exposure when the picture is taken.
34852 SpectralSensitivity Indicates the spectral sensitivity of each channel of the camera used.
34855 ISOSpeedRatings Indicates the ISO Speed and ISO Latitude of the camera or input device as specified in ISO 12232.
34856 OECF Indicates the Opto-Electric Conversion Function (OECF) specified in ISO 14524.
36864 ExifVersion The version of the supported Exif standard.
36867 DateTimeOriginal The date and time when the original image data was generated.
36868 DateTimeDigitized The date and time when the image was stored as digital data.
37121 ComponentsConfiguration Specific to compressed data; specifies the channels and complements PhotometricInterpretation
37122 CompressedBitsPerPixel Specific to compressed data; states the compressed bits per pixel.
37377 ShutterSpeedValue Shutter speed.
37378 ApertureValue The lens aperture.
37379 BrightnessValue The value of brightness.
37380 ExposureBiasValue The exposure bias.
37381 MaxApertureValue The smallest F number of the lens.
37382 SubjectDistance The distance to the subject, given in meters.
37383 MeteringMode The metering mode.
37384 LightSource The kind of light source.
37385 Flash Indicates the status of flash when the image was shot.
37386 FocalLength The actual focal length of the lens, in mm.
37396 SubjectArea Indicates the location and area of the main subject in the overall scene.
37500 MakerNote Manufacturer specific information.
37510 UserComment Keywords or comments on the image; complements ImageDescription.
37520 SubsecTime A tag used to record fractions of seconds for the DateTime tag.
37521 SubsecTimeOriginal A tag used to record fractions of seconds for the DateTimeOriginal tag.
37522 SubsecTimeDigitized A tag used to record fractions of seconds for the DateTimeDigitized tag.
40960 FlashpixVersion The Flashpix format version supported by a FPXR file.
40961 ColorSpace The colour space information tag is always recorded as the colour space specifier.
40962 PixelXDimension Specific to compressed data; the valid width of the meaningful image.
40963 PixelYDimension Specific to compressed data; the valid height of the meaningful image.
40964 RelatedSoundFile Used to record the name of an audio file related to the image data.
41483 FlashEnergy Indicates the strobe energy at the time the image is captured, as measured in Beam Candle Power Seconds
41484 SpatialFrequencyResponse Records 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.
41486 FocalPlaneXResolution Indicates the number of pixels in the image width (X) direction per FocalPlaneResolutionUnit on the camera focal plane.
41487 FocalPlaneYResolution Indicates the number of pixels in the image height (Y) direction per FocalPlaneResolutionUnit on the camera focal plane.
41488 FocalPlaneResolutionUnit Indicates the unit for measuring FocalPlaneXResolution and FocalPlaneYResolution.
41492 SubjectLocation Indicates the location of the main subject in the scene.
41493 ExposureIndex Indicates the exposure index selected on the camera or input device at the time the image is captured.
41495 SensingMethod Indicates the image sensor type on the camera or input device.
41728 FileSource Indicates the image source.
41729 SceneType Indicates the type of scene.
41730 CFAPattern Indicates the colour filter array (CFA) geometric pattern of the image sensor when a one-chip colour area sensor is used.
41985 CustomRendered Indicates the use of special processing on image data, such as rendering geared to output.
41986 ExposureMode Indicates the exposure mode set when the image was shot.
41987 WhiteBalance Indicates the white balance mode set when the image was shot.
41988 DigitalZoomRatio Indicates the digital zoom ratio when the image was shot.
41989 FocalLengthIn35mmFilm Indicates the equivalent focal length assuming a 35mm film camera, in mm.
41990 SceneCaptureType Indicates the type of scene that was shot.
41991 GainControl Indicates the degree of overall image gain adjustment.
41992 Contrast Indicates the direction of contrast processing applied by the camera when the image was shot.
41993 Saturation Indicates the direction of saturation processing applied by the camera when the image was shot.
41994 Sharpness Indicates the direction of sharpness processing applied by the camera when the image was shot.
41995 DeviceSettingDescription This tag indicates information on the picture-taking conditions of a particular camera model.
41996 SubjectDistanceRange Indicates the distance to the subject.
42016 ImageUniqueID Indicates an identifier assigned uniquely to each image.

Code

Name

Short description
0 GPSVersionID Indicates the version of GPSInfoIFD.
1 GPSLatitudeRef Indicates whether the latitude is north or south latitude.
2 GPSLatitude Indicates the latitude.
3 GPSLongitudeRef Indicates whether the longitude is east or west longitude.
4 GPSLongitude Indicates the longitude.
5 GPSAltitudeRef Indicates the altitude used as the reference altitude.
6 GPSAltitude Indicates the altitude based on the reference in GPSAltitudeRef.
7 GPSTimeStamp Indicates the time as UTC (Coordinated Universal Time).
8 GPSSatellites Indicates the GPS satellites used for measurements.
9 GPSStatus Indicates the status of the GPS receiver when the image is recorded.
10 GPSMeasureMode Indicates the GPS measurement mode.
11 GPSDOP Indicates the GPS DOP (data degree of precision).
12 GPSSpeedRef Indicates the unit used to express the GPS receiver speed of movement.
13 GPSSpeed Indicates the speed of GPS receiver movement.
14 GPSTrackRef Indicates the reference for giving the direction of GPS receiver movement.
15 GPSTrack Indicates the direction of GPS receiver movement.
16 GPSImgDirectionRef Indicates the reference for giving the direction of the image when it is captured.
17 GPSImgDirection Indicates the direction of the image when it was captured.
18 GPSMapDatum Indicates the geodetic survey data used by the GPS receiver.
19 GPSDestLatitudeRef Indicates whether the latitude of the destination point is north or south latitude.
20 GPSDestLatitude Indicates the latitude of the destination point.
21 GPSDestLongitudeRef Indicates whether the longitude of the destination point is east or west longitude.
22 GPSDestLongitude Indicates the longitude of the destination point.
23 GPSDestBearingRef Indicates the reference used for giving the bearing to the destination point.
24 GPSDestBearing Indicates the bearing to the destination point.
25 GPSDestDistanceRef Indicates the unit used to express the distance to the destination point.
26 GPSDestDistance Indicates the distance to the destination point.
27 GPSProcessingMethod A character string recording the name of the method used for location finding.
28 GPSAreaInformation A character string recording the name of the GPS area.
29 GPSDateStamp A character string recording date and time information relative to UTC (Coordinated Universal Time).
30 GPSDifferential Indicates whether differential correction is applied to the GPS receiver.

Code

Name

Short description
1 InteroperabilityIndex Indicates the identification of the Interoperability rule.

The codes used by the thumbnail IFD are exactly the same as for the Primary Image IFD.