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:

Primary Image IFD (Primary)
EXIF specific IFD (Exif)
GPS (Global Positioning System) IFD (GPS)
Interoperability IFD (Interopability)
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.

Primary Image IFD (IFD = 1)

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 color 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 color map for palette color images.
338	ExtraSamples	Description of extra components.
33432	Copyright	Copyright notice.

EXIF IFD (IFD = 2)

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 color space information tag is always recorded as the color 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 color filter array (CFA) geometric pattern of the image sensor when a one-chip color 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.

GPS IFD (IFD = 3)

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.

Interoperability IFD (IFD = 4)

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

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