Graphics.HsExif

Ability to work with the EXIF data contained in JPEG files.

Documentation

EXIF parsing from JPEG files. EXIF tags are enumerated as ExifTag values, check exposureTime for instance. If you use the predefined ExifTag values, you don't care about details of the ExifTag type, however you should check out the ExifValue type.

Regarding the ExifTag type there is however a field of that type that may interest you: prettyPrinter. It's a function that'll format nicely an exif value for that exif tag as a String. For instance for the flash ExifTag, it'll say whether the flash was fired or not, if there was return light and so on.

Generally speaking, you start from a JPEG file, you can parse its exif tags as a Map of ExifTag to ExifValue using parseExif or parseFileExif. You can enumerate the map or lookup the tags that interest you.

There are also a couple of higher-level helpers like getOrientation, getDateTimeOriginal, wasFlashFired and getGpsLatitudeLongitude.

When building on Windows if you have trouble with the iconv library, you may build without that dependency: cabal install -f-iconv. That way you loose nice decoding of the EXIF User Comment though.

Main functions

parseFileExif :: FilePath -> IO (Either String (Map ExifTag ExifValue))

Read EXIF data from the file you give. It's a key-value map. The reading is strict to avoid file handle exhaustion on a recursive reading of a directory tree.

parseExif :: ByteString -> Either String (Map ExifTag ExifValue)

Read EXIF data from a lazy bytestring.

Higher-level helper functions

readExifDateTime :: String -> Maybe LocalTime

Decode an EXIF date time value. Will return Nothing in case parsing fails.

getDateTimeOriginal :: Map ExifTag ExifValue -> Maybe LocalTime

Extract the date and time when the picture was taken from the EXIF information.

getOrientation :: Map ExifTag ExifValue -> Maybe ImageOrientation

Extract the image orientation from the EXIF information. Will return Nothing on parse error.

data ImageOrientation

Constructors

Normal

Mirror

Rotation RotationDirection

MirrorRotation RotationDirection

Instances

Eq ImageOrientation

Methods

(==) :: ImageOrientation -> ImageOrientation -> Bool

(/=) :: ImageOrientation -> ImageOrientation -> Bool

Show ImageOrientation

Methods

showsPrec :: Int -> ImageOrientation -> ShowS

show :: ImageOrientation -> String

showList :: [ImageOrientation] -> ShowS

data RotationDirection

Constructors

MinusNinety

Ninety

HundredAndEighty

Instances

Eq RotationDirection

Methods

(==) :: RotationDirection -> RotationDirection -> Bool

(/=) :: RotationDirection -> RotationDirection -> Bool

Show RotationDirection

Methods

showsPrec :: Int -> RotationDirection -> ShowS

show :: RotationDirection -> String

showList :: [RotationDirection] -> ShowS

getGpsLatitudeLongitude :: Map ExifTag ExifValue -> Maybe (Double, Double)

Extract the GPS latitude and longitude where the picture was taken (if it is present in the EXIF)

wasFlashFired :: Map ExifTag ExifValue -> Maybe Bool

Will return Just True if the flash was fired, Just False if it was not, and Nothing if the file does not contain the information.

formatAsFloatingPoint :: Int -> ExifValue -> String

Format the exif value as floating-point if it makes sense, otherwise use the default show implementation. The first parameter lets you specify how many digits after the comma to format in the result string. The special behaviour applies only for ExifRational and ExifRationalList.

getGpsDateTime :: Map ExifTag ExifValue -> Maybe LocalTime

Extract the GPS date time, if present in the picture.

parseGpsTime :: ExifValue -> Maybe TimeOfDay

read the GPS time from the gpsTimeStamp field.

The ExifValue type

data ExifValue

An exif value.

If you want a string describing the contents of the value, simply use show.

Constructors

ExifNumber !Int

An exif number. Originally it could have been short, int, signed or not.

ExifText !String

ASCII text.

ExifRational !Int !Int

A rational number (numerator, denominator). Sometimes we're used to it as rational (exposition time: 1/160), sometimes as float (exposure compensation, we rather think -0.75) show will display it as 1/160.

ExifNumberList ![Int]

List of numbers. Originally they could have been short, int, signed or not.

ExifRationalList ![(Int, Int)]

A list of rational numbers (numerator, denominator). Sometimes we're used to it as rational (exposition time: 1/160), sometimes as float (exposure compensation, we rather think -0.75) show will display it as 1/160.

ExifUndefined !ByteString

The undefined type in EXIF means that the contents are not specified and up to the manufacturer. In effect it's exactly a bytestring. Sometimes it's text with ASCII or UNICODE at the beginning, often it's binary in nature.

ExifUnknown !Word16 !Int !Int

Unknown exif value type. All EXIF 2.3 types are supported, it could be a newer file. The parameters are type, count then value

Instances

Eq ExifValue

Methods

(==) :: ExifValue -> ExifValue -> Bool

(/=) :: ExifValue -> ExifValue -> Bool

Ord ExifValue

Methods

compare :: ExifValue -> ExifValue -> Ordering

(<) :: ExifValue -> ExifValue -> Bool

(<=) :: ExifValue -> ExifValue -> Bool

(>) :: ExifValue -> ExifValue -> Bool

(>=) :: ExifValue -> ExifValue -> Bool

max :: ExifValue -> ExifValue -> ExifValue

min :: ExifValue -> ExifValue -> ExifValue

Show ExifValue

Methods

showsPrec :: Int -> ExifValue -> ShowS

show :: ExifValue -> String

showList :: [ExifValue] -> ShowS

Most useful exif tags

exposureTime :: ExifTag

fnumber :: ExifTag

isoSpeedRatings :: ExifTag

dateTimeOriginal :: ExifTag

shutterSpeedValue :: ExifTag

apertureValue :: ExifTag

brightnessValue :: ExifTag

exposureBiasValue :: ExifTag

maxApertureValue :: ExifTag

flash :: ExifTag

focalLength :: ExifTag

userComment :: ExifTag

orientation :: ExifTag

make :: ExifTag

model :: ExifTag

software :: ExifTag

copyright :: ExifTag

digitalZoomRatio :: ExifTag

focalLengthIn35mmFilm :: ExifTag

artist :: ExifTag

GPS related exif tags

gpsVersionID :: ExifTag

gpsLatitudeRef :: ExifTag

gpsLatitude :: ExifTag

gpsLongitudeRef :: ExifTag

gpsLongitude :: ExifTag

gpsAltitudeRef :: ExifTag

gpsAltitude :: ExifTag

gpsTimeStamp :: ExifTag

gpsSatellites :: ExifTag

gpsStatus :: ExifTag

gpsMeasureMode :: ExifTag

gpsDop :: ExifTag

gpsSpeedRef :: ExifTag

gpsSpeed :: ExifTag

gpsTrackRef :: ExifTag

gpsTrack :: ExifTag

gpsImgDirectionRef :: ExifTag

gpsImgDirection :: ExifTag

gpsMapDatum :: ExifTag

gpsDestLatitudeRef :: ExifTag

gpsDestLatitude :: ExifTag

gpsDestLongitudeRef :: ExifTag

gpsDestLongitude :: ExifTag

gpsDestBearingRef :: ExifTag

gpsDestBearing :: ExifTag

gpsDestDistanceRef :: ExifTag

gpsDestDistance :: ExifTag

gpsProcessingMethod :: ExifTag

gpsAreaInformation :: ExifTag

gpsDateStamp :: ExifTag

gpsDifferential :: ExifTag

Less useful exif tags

exifVersion :: ExifTag

sensingMethod :: ExifTag

fileSource :: ExifTag

sceneType :: ExifTag

makerNote :: ExifTag

subjectDistance :: ExifTag

meteringMode :: ExifTag

lightSource :: ExifTag

exifImageWidth :: ExifTag

exifImageHeight :: ExifTag

relatedSoundFile :: ExifTag

focalPlaneXResolution :: ExifTag

focalPlaneYResolution :: ExifTag

focalPlaneResolutionUnit :: ExifTag

dateTimeDigitized :: ExifTag

componentConfiguration :: ExifTag

compressedBitsPerPixel :: ExifTag

exposureProgram :: ExifTag

spectralSensitivity :: ExifTag

oecf :: ExifTag

subjectArea :: ExifTag

subSecTime :: ExifTag

subSecTimeOriginal :: ExifTag

subSecTimeDigitized :: ExifTag

flashPixVersion :: ExifTag

colorSpace :: ExifTag

flashEnergy :: ExifTag

spatialFrequencyResponse :: ExifTag

subjectLocation :: ExifTag

exposureIndex :: ExifTag

cfaPattern :: ExifTag

customRendered :: ExifTag

exposureMode :: ExifTag

whiteBalance :: ExifTag

sceneCaptureType :: ExifTag

gainControl :: ExifTag

contrast :: ExifTag

saturation :: ExifTag

sharpness :: ExifTag

deviceSettingDescription :: ExifTag

subjectDistanceRange :: ExifTag

imageUniqueId :: ExifTag

exifInteroperabilityOffset :: ExifTag

imageDescription :: ExifTag

xResolution :: ExifTag

yResolution :: ExifTag

resolutionUnit :: ExifTag

dateTime :: ExifTag

whitePoint :: ExifTag

primaryChromaticities :: ExifTag

yCbCrPositioning :: ExifTag

yCbCrCoefficients :: ExifTag

referenceBlackWhite :: ExifTag

exifIfdOffset :: ExifTag

printImageMatching :: ExifTag

gpsTagOffset :: ExifTag

If you need to declare your own exif tags

data ExifTag

An exif tag. Normally you don't need to fiddle with this, except maybe if the library doesn't know the particular exif tag you're interested in. Rather check the list of supported exif tags, like exposureTime and so on.

Constructors

ExifTag

Fields

• tagLocation :: TagLocation

  In which part of the JPEG file the exif tag was found

• tagDesc :: Maybe String

  Description of the exif tag (exposureTime, fnumber...) or if unknown, Nothing. This should be purely for debugging purposes, to compare tags use == on ExifTag or compare the tagKey.

• tagKey :: Word16

  Exif tag key, the number uniquely identifying this tag.

• prettyPrinter :: ExifValue -> Text

  A function that'll display nicely an exif value for that exif tag. For instance for the flash ExifTag, it'll say whether the flash was fired or not, if there was return light and so on.

Instances

Eq ExifTag

Methods

(==) :: ExifTag -> ExifTag -> Bool

(/=) :: ExifTag -> ExifTag -> Bool

Ord ExifTag

Methods

compare :: ExifTag -> ExifTag -> Ordering

(<) :: ExifTag -> ExifTag -> Bool

(<=) :: ExifTag -> ExifTag -> Bool

(>) :: ExifTag -> ExifTag -> Bool

(>=) :: ExifTag -> ExifTag -> Bool

max :: ExifTag -> ExifTag -> ExifTag

min :: ExifTag -> ExifTag -> ExifTag

Show ExifTag

Methods

showsPrec :: Int -> ExifTag -> ShowS

show :: ExifTag -> String

showList :: [ExifTag] -> ShowS

data TagLocation

Location of the tag in the JPG file structure. Normally you don't need to fiddle with this, except maybe if the library doesn't know the particular exif tag you're interested in. Rather check the list of supported exif tags, like exposureTime and so on.

Constructors

ExifSubIFD

IFD0

GpsSubIFD

Instances

Eq TagLocation

Methods

(==) :: TagLocation -> TagLocation -> Bool

(/=) :: TagLocation -> TagLocation -> Bool

Ord TagLocation

Methods

compare :: TagLocation -> TagLocation -> Ordering

(<) :: TagLocation -> TagLocation -> Bool

(<=) :: TagLocation -> TagLocation -> Bool

(>) :: TagLocation -> TagLocation -> Bool

(>=) :: TagLocation -> TagLocation -> Bool

max :: TagLocation -> TagLocation -> TagLocation

min :: TagLocation -> TagLocation -> TagLocation

Show TagLocation

Methods

showsPrec :: Int -> TagLocation -> ShowS

show :: TagLocation -> String

showList :: [TagLocation] -> ShowS