Exif

Crystal C bindings for libexif.

Provides basic support for reading EXIF tags on files using libexif and Crystal.

Installation

Get libexif for your OS:

# MacOS
brew install libexif pkgconf

# Debian/Ubuntu
apt-get install -y libexif-dev pkg-config

# RedHat/Fedora
dnf install -y libexif-devel

Add the dependency to your shard.yml:

dependencies:
  exif:
    github: mamantoha/crystal-exif

Run shards install

Usage

This is an example on how to read EXIF data from a file:

require "exif"

The image is taken from exif-samples repository.

Load EXIF data from a JPEG file

file = File.open("metadata_test.jpg")
exif = Exif.new(file)
exif.data

EXIF data can also be read from memory or any IO:

exif = Exif.new(image_bytes)
exif = Exif.new(io)

{"compression" => "JPEG compression",
 "image_description" => "",
 "make" => "NIKON",
 "model" => "COOLPIX P6000",
 "orientation" => "Top-left",
 "x_resolution" => "300",
 "y_resolution" => "300",
 "resolution_unit" => "Inch",
 "software" => "Nikon Transfer 1.1 W",
 "date_time" => "2008:11:01 21:15:07",
 "ycbcr_positioning" => "Centered",
 "exposure_time" => "1/75 sec.",
 "fnumber" => "f/5.9",
 "exposure_program" => "Normal program",
 "iso_speed_ratings" => "64",
 "exif_version" => "Exif Version 2.2",
 "date_time_original" => "2008:10:22 16:28:39",
 "date_time_digitized" => "2008:10:22 16:28:39",
 "components_configuration" => "Y Cb Cr -",
 "exposure_bias_value" => "0.00 EV",
 "max_aperture_value" => "2.90 EV (f/2.7)",
 "metering_mode" => "Pattern",
 "light_source" => "Unknown",
 "flash" => "Flash did not fire, compulsory flash mode",
 "focal_length" => "24.0 mm",
 "maker_note" => "3298 bytes undefined data",
 "user_comment" => "",
 "flash_pix_version" => "FlashPix Version 1.0",
 "color_space" => "sRGB",
 "pixel_x_dimension" => "640",
 "pixel_y_dimension" => "480",
 "file_source" => "DSC",
 "scene_type" => "Directly photographed",
 "custom_rendered" => "Normal process",
 "exposure_mode" => "Auto exposure",
 "white_balance" => "Auto white balance",
 "digital_zoom_ratio" => "0.00",
 "focal_length_in35_mm_film" => "112",
 "scene_capture_type" => "Standard",
 "gain_control" => "Normal",
 "contrast" => "Normal",
 "saturation" => "Normal",
 "sharpness" => "Normal",
 "subject_distance_range" => "Unknown",
 "gps_latitude_ref" => "N",
 "gps_latitude" => "43, 28, 2.81400000",
 "gps_longitude_ref" => "E",
 "gps_longitude" => "11, 53, 6.45599999",
 "gps_altitude_ref" => "Sea level",
 "gps_time_stamp" => "14:27:07.24",
 "gps_satellites" => "06",
 "gps_img_direction_ref" => "",
 "gps_map_datum" => "WGS-84",
 "gps_date_stamp" => "2008:10:23"}

Return an Exif entry for the given tag

file = File.open("metadata_test.jpg")
exif = Exif.new(file)
exif.make # => "NIKON"
exif.model # => "COOLPIX P6000"

Read typed EXIF entries

Use entry when the tag's IFD, format, components, or raw bytes are needed:

exif = Exif.new("metadata_test.jpg")
entry = exif.entry(LibExif::ExifTag::ExifTagModel)

if entry
  entry.ifd           # => LibExif::ExifIfd::ExifIfd0
  entry.format        # => LibExif::ExifFormat::ExifFormatAscii
  entry.components    # => 14
  entry.raw_bytes     # => Bytes[67, 79, 79, ...]
  entry.display_value # => "COOLPIX P6000"
end

Numeric entries can be decoded according to their format and byte order:

orientation = exif.entry(LibExif::ExifTag::ExifTagOrientation)
orientation.try &.short # => 1

latitude = exif.entry(LibExif::ExifTag::ExifTagGpsLatitude)
latitude.try &.rational(0) # => LibExif::ExifRational(@numerator=43, @denominator=1)

Available numeric decoders are short, sshort, long, slong, rational, and srational.

Use entries to access every entry, including tags that occur in more than one IFD.

Return the MakerNote data out of the EXIF data

file = File.open("metadata_test.jpg")
exif = Exif.new(file)
exif.mnote_data

{"Firmware" => "0210",
 "ISO" => "ISO 0",
 "ColorMode1" => "COLOR",
 "Quality" => "FINE",
 "WhiteBalance" => "AUTO",
 "Sharpening" => "NORMAL",
 "FocusMode" => "AF-S",
 "FlashSetting" => "",
 "ISOSelection" => "AUTO",
 "FaceDetect" => "8 bytes unknown data: 01004001f0000000",
 "ActiveDLighting" => "0",
 "ImageAdjustment" => "NORMAL",
 "ToneCompensation" => "NORMAL",
 "Adapter" => "OFF",
 "DigitalZoom" => "1.000",
 "AFFocusPosition" => "AF position: center",
 "ShotInfo" => "18 bytes unknown data: 000000000e00000000000000000044430000",
 "Saturation" => "0",
 "NoiseReduction," => "OFF",
 "RetouchHistory" => "Invalid number of components (6, expected 1).",
 "Saturation2" => "NORMAL",
 "CaptureEditorVer" => "COOLPIX P6000V1.0"}

Development

crystal ./lib/crystal_lib/src/main.cr src/exif/lib_exif.cr.in > src/exif/lib_exif.cr

Contributing

Fork it (https://github.com/mamantoha/crystal-exif/fork)
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create a new Pull Request

Contributors

Anton Maminov - creator and maintainer