libexif — PPM Packages

libexif clib

EXIF metadata reader and writer for PascalAI. Read GPS coordinates, camera settings, orientation, timestamps, and lens data from JPEG photos. Edit or strip metadata for privacy. The standard library used by photo management and geotagging tools.

Version1.0.0

Typeclib

System reqlibexif-dev

CategoryMultimedia

ppm install libexif

CLib package — system library required

Ubuntu/Debian: sudo apt install libexif-dev • Fedora: sudo dnf install libexif-devel • macOS: brew install libexif

Quick Start

uses libexif;

var exif := LoadFromFile('/photos/IMG_1234.jpg');
var gps := GetGPS(exif);
if gps.HasGPS then
  WriteLn('Location: ' + FloatToStr(gps.Latitude) + ', ' +
          FloatToStr(gps.Longitude));

var cam := GetCameraInfo(exif);
WriteLn('Camera: ' + cam.Make + ' ' + cam.Model);
WriteLn('ISO: ' + IntToStr(cam.ISO) + '  f/' + FloatToStr(cam.Aperture));
WriteLn('Shutter: 1/' + IntToStr(Round(1/cam.ShutterSpeed)));
FreeData(exif);

uses libexif;

{ Strip EXIF for privacy before publishing }
StripEXIF('/private/photo.jpg', '/public/photo.jpg');

{ Fix orientation (rotate pixel data based on EXIF tag) }
FixOrientation('/input/photo.jpg', '/output/photo.jpg');

{ Export all metadata as JSON }
var exif := LoadFromFile('/photos/photo.jpg');
var json := ToJSON(exif);
WriteLn(json);
FreeData(exif);

Load / Save API

All operations work on an opaque TExifData handle. Always call FreeData when done to release memory.

Function	Description
LoadFromFile(path)	Load EXIF data from a JPEG file. Returns `TExifData` handle.
LoadFromBytes(data)	Load EXIF from an in-memory byte array (JPEG data).
SaveToFile(exif, srcPath, dstPath)	Write modified EXIF back into a new JPEG file.
SaveInPlace(exif, path)	Overwrite the EXIF segment of an existing JPEG file.
FreeData(exif)	Release memory for a `TExifData` handle.
HasEXIF(path)	Returns True if the JPEG file contains an EXIF segment.

Reading Entries API

Low-level access to individual EXIF tags by numeric ID or name. Use the Structured Access API below for common fields.

Function	Description
GetEntryString(exif, tagId)	Read tag value as a formatted string. Returns empty string if not present.
GetEntryInt(exif, tagId)	Read tag value as integer. Raises exception if tag absent.
GetEntryFloat(exif, tagId)	Read rational tag (e.g. exposure time) as floating-point.
GetEntryBytes(exif, tagId)	Read tag raw bytes.
HasEntry(exif, tagId)	Returns True if tag exists in any IFD.
ListTags(exif)	Returns array of all tag IDs present.
TagName(tagId)	Human-readable tag name for a numeric ID. E.g. 0x010F → 'Make'.

uses libexif;

var exif := LoadFromFile('photo.jpg');

{ Low-level tag reads }
var make := GetEntryString(exif, $010F);   { Make }
var iso  := GetEntryInt(exif, $8827);       { ISOSpeedRatings }
var exp  := GetEntryFloat(exif, $829A);    { ExposureTime }

WriteLn('Make: '     + make);
WriteLn('ISO: '      + IntToStr(iso));
WriteLn('Exposure: ' + FloatToStr(exp) + 's');

{ List all tags }
var tags := ListTags(exif);
for var tid in tags do
  WriteLn(TagName(tid) + ': ' + GetEntryString(exif, tid));

FreeData(exif);

Structured Access API

High-level functions that parse common EXIF groups into typed records.

Function	Description
GetGPS(exif)	Returns `TExifGPS` with latitude, longitude, altitude, heading, and speed.
GetCameraInfo(exif)	Returns `TExifCameraInfo` with make, model, ISO, aperture, shutter, focal length.
GetDateTime(exif)	Returns `TDateTime` parsed from the DateTimeOriginal tag.
GetDateTimeStr(exif)	Returns DateTimeOriginal as a string in 'YYYY:MM:DD HH:MM:SS' format.
GetOrientation(exif)	Returns orientation value 1–8 (EXIF rotation/flip code).
GetThumbnail(exif)	Returns embedded JPEG thumbnail as byte array, or empty if absent.
GetSoftware(exif)	Software tag value (editing app name, e.g. 'Lightroom').
GetFlash(exif)	Returns True if flash fired.
GetWhiteBalance(exif)	Returns 'Auto' or 'Manual'.

Writing Entries API

Function	Description
SetEntryString(exif, tagId, value)	Write or update a string tag.
SetEntryInt(exif, tagId, value)	Write or update an integer tag.
SetEntryRational(exif, tagId, num, den)	Write a rational tag as numerator/denominator.
SetGPS(exif, lat, lon, alt)	Write GPS IFD tags (latitude, longitude, altitude).
SetDateTime(exif, dt)	Write DateTimeOriginal from a `TDateTime` value.
SetOrientation(exif, value)	Set orientation tag (1–8).
RemoveEntry(exif, tagId)	Delete a specific tag.
RemoveGPS(exif)	Delete all GPS IFD tags.

uses libexif;

var exif := LoadFromFile('photo.jpg');

{ Update GPS coordinates }
SetGPS(exif, 40.41650, -3.70379, 667.0);  { Madrid, 667m }

{ Update timestamp }
SetDateTime(exif, Now());

{ Remove identifying tags }
RemoveEntry(exif, $013B);   { Artist }
RemoveEntry(exif, $8298);   { Copyright }

SaveToFile(exif, 'photo.jpg', 'photo_updated.jpg');
FreeData(exif);

Convenience API

Function	Description
StripEXIF(srcPath, dstPath)	Copy JPEG removing all metadata. Output is clean for publishing.
FixOrientation(srcPath, dstPath)	Rotate/flip pixel data to match orientation tag, then clear tag.
ToJSON(exif)	Serialize all EXIF tags to a JSON string.
FromJSON(json)	Create a `TExifData` handle populated from a JSON string.
CopyEXIF(srcPath, dstPath)	Copy EXIF segment from `srcPath` into `dstPath` (must both be JPEG).
EXIFVersion()	Returns libexif library version string.

TExifGPS Record

Field	Type	Description
HasGPS	Boolean	False if no GPS IFD present in file.
Latitude	Double	Decimal degrees. Negative = South.
Longitude	Double	Decimal degrees. Negative = West.
Altitude	Double	Meters above sea level. Negative if below.
Heading	Double	True north heading in degrees (0–360), or -1 if absent.
Speed	Double	Speed in km/h at capture time, or -1 if absent.
Timestamp	String	GPS timestamp string 'HH:MM:SS'.
Datestamp	String	GPS datestamp string 'YYYY:MM:DD'.

TExifCameraInfo Record

Field	Type	Description
Make	String	Camera manufacturer (e.g. 'Apple', 'Canon', 'Sony').
Model	String	Camera model string (e.g. 'iPhone 15 Pro', 'EOS R5').
LensMake	String	Lens manufacturer, if present.
LensModel	String	Lens model string, if present.
ISO	Integer	ISO speed (e.g. 100, 800, 3200).
Aperture	Double	F-number (e.g. 1.8, 4.0, 11.0).
ShutterSpeed	Double	Exposure time in seconds (e.g. 0.001 = 1/1000s).
FocalLength	Double	Focal length in mm.
FocalLength35mm	Integer	35mm-equivalent focal length, or 0 if absent.
ExposureMode	String	'Auto', 'Manual', or 'Auto bracket'.
ExposureProgram	String	'Normal', 'Aperture priority', 'Shutter priority', etc.
MeteringMode	String	'Matrix', 'Center-weighted', 'Spot', etc.

Common EXIF Tag IDs

Tag ID	Name	Description
0x010F	Make	Camera manufacturer string.
0x0110	Model	Camera model string.
0x0112	Orientation	1–8 rotation/flip code.
0x011A	XResolution	Horizontal resolution (DPI).
0x011B	YResolution	Vertical resolution (DPI).
0x0132	DateTime	File modification date/time.
0x013B	Artist	Photographer name.
0x8298	Copyright	Copyright string.
0x829A	ExposureTime	Shutter speed as rational (e.g. 1/1000).
0x829D	FNumber	F-number (aperture) as rational.
0x8827	ISOSpeedRatings	ISO sensitivity value.
0x9003	DateTimeOriginal	Original capture date/time.
0x9004	DateTimeDigitized	Date/time image was digitized.
0x920A	FocalLength	Focal length in mm.
0xA405	FocalLengthIn35mmFilm	35mm-equivalent focal length.
0xA432	LensSpecification	Min/max focal length and aperture.
0xA434	LensModel	Lens model string.
0x8825	GPSInfo	Offset to GPS sub-IFD.

Memory management

Every LoadFromFile or LoadFromBytes call allocates a handle. Always call FreeData(exif) when finished. Handles are not garbage-collected automatically.