LightLog Metadata 101

• If you have never heard of photo metadata before, we recommend reading this article end to end so you can quickly understand what metadata is, what it is for, and what LightLog does with it.
• If you already know the basics of photo metadata, you can start from 4) Why use LightLog to record metadata?.

1) What is photo metadata?

Let’s make one key distinction first to avoid confusion in a film-photography context:

• Unless otherwise noted, the word “photo” in this article refers to a digital photo file (for example, an image in your system photo library, or a file produced after scanning film).
• It does not mean a physical print in your hand, nor the physical film original itself.

In other words, the metadata discussed here is mainly information that “travels with digital files,” not information written on physical media.

1.1 What a photo file is made of

If you think of a photo as a “file package,” it usually contains two parts:

1. The image itself (pixel content).
2. Information describing that image (metadata).

This descriptive information may include capture time, camera model, focal length, exposure settings, geolocation, photographer, editing software, and more.

1.2 The role of metadata

You can think of metadata as a single photo’s “instruction manual + memory tags”:

• Instruction manual: helps software understand information beyond the image content itself.
• Memory tags: help you review how a shot was taken (film keeps getting more expensive; effective review helps reduce wasted frames and save money).

1.3 EXIF and common photo file formats

In digital photography, the most common metadata format is EXIF.

For a clear and comprehensive explanation of EXIF, we recommend Nasim Mansurov’s article on Photography Life: EXIF Data Explained.

In simple terms, one of LightLog’s major functions is to help you record shooting information and write it into the EXIF data of scanned files.

Not every image format supports carrying EXIF data equally well. Generally, JPEG, HEIF (HEIC), TIFF, FFF, and RAW formats (such as DNG, CR2, and ARW) have good EXIF support, while PNG and BMP have historically been less friendly to EXIF (the good news is that in 2025, the W3C formally included EXIF in the PNG Third Edition specification).

2) Key metadata differences between digital and film photography

Most digital cameras or phones automatically write a large amount of EXIF data when shooting (shutter, aperture, ISO, camera model, lens, capture time, etc.).

Film workflows are quite different:

• Scanners or digital cameras used to digitize film do not know your original shooting parameters.
• Photo metadata standards were built around digital photography, so some film-specific information—such as film stock, Exposure Index (EI), lab, and scanner model—is not covered by standard EXIF fields.

So a common pain point for film users is: the photo is preserved, but the settings and intent behind each shot are easily lost. This directly affects later review and the ability to reproduce consistent results.

3) Why do you need metadata for photos?

For film photographers, metadata is not only about “seeing settings,” but more importantly:

• Reviewing experience: preserving exposure decisions and gear combinations behind good photos.
• Troubleshooting: when results look abnormal, helping you quickly determine whether the issue came from exposure settings, lens, development, or scanning.
• Long-term management: better organization in your system photo library, Lightroom, Capture One or other photo-management software by gear, location, and time.

4) Why use LightLog to record metadata?

4.1 Pain points in traditional workflows

In film photography, “recording metadata” is not a new need. A traditional workflow is usually: take notes while shooting, then write metadata into files one by one after receiving scans, often using tools like ExifTool.

Common issues in that workflow:

• Recording may interrupt your shooting rhythm.
• Post-processing and data organization have a steep learning curve, and many fields require manual maintenance.
• Backfilling GPS information after the fact is difficult.

(To be clear, ExifTool is a foundational piece of infrastructure in the field of image metadata processing. Many professional and automated workflows rely on it, and it also played an important role during LightLog’s testing process. The issue discussed here is not a lack of tool capability, but the learning and operational cost for everyday users to manually record, match, and write metadata.)

4.2 What LightLog improves

LightLog focuses on improving two parts of the experience:

1. Less friction while shooting: most metadata can be preset. During capture, simple operations on one screen are enough to complete metadata recording quickly, with minimal interruption.
2. Batch processing after scanning: with little to no manual rework, scanned files can be batch matched to LightLog records by filename or selection order (we have to say: this flow is really smooth), then all files can be written with EXIF and exported to the system photo library in one tap.

5) What metadata does LightLog record?

5.1 LightLog metadata overview

5.2 About the UserComment field

UserComment is a reserved EXIF field intended for users or software to freely store supplementary notes.

LightLog writes metadata to corresponding standard EXIF fields whenever possible. But as noted above, not all film semantics have corresponding standard EXIF fields. So to preserve your shooting information as completely as possible in your photo files, LightLog concatenates that part of the information and writes it into the UserComment field.

In the current version, the value written into UserComment uses a structured and human-readable text format, and appears as readable text in external tools.

Note: UserComment can be displayed differently across software. That difference is due to third-party EXIF support behavior, not a LightLog write failure.

5.3 How LightLog handles metadata writing

1. If the original file already contains EXIF fields that LightLog plans to write, LightLog overwrites those existing values.
2. For other fields that LightLog does not write or modify, LightLog preserves existing data whenever possible.

5.4 Current limitations

The current version of LightLog supports exporting photo files after writing metadata, but does not yet support:

• Exporting metadata itself as standalone data documents such as CSV or JSON.
• Exporting metadata as XMP sidecar files; for users who digitize film into RAW with digital cameras and prefer not to modify the original files, this can be inconvenient.

Among these, document export is already planned and will be provided in a future free update for all users.

LightLog will not monetize by restricting your ownership of your own data :)

6) Which data depends on system permissions?

Some LightLog recording capabilities depend on system permissions, which you can disable anytime in iOS Settings:

• Camera permission: used for reference-photo capture. If disabled, you can still record metadata for each exposure, but later scan matching may be less convenient.
• Location permission (while using the app): used to record shooting locations. If disabled, GPS-related data cannot be recorded, but other functions remain unaffected.
• Photos permission (full access): used to select images from the system photo library for matching and to export metadata-embedded photos back to the photo library. If disabled, scan matching and export will be unavailable, which affects LightLog’s core functionality.

LightLog can run fully offline. All recording data is saved locally by default and is not uploaded to developer servers (in fact, we do not operate any servers; even the LightLog website is a static site hosted on Cloudflare). The current version also does not include third-party analytics, behavioral tracking, or ad SDKs. If you still have concerns about network activity, you can manually disable LightLog cellular data access in system settings.

For more privacy details, see the LightLog Privacy Policy.

7) What is EI?

Let’s first clarify two concepts around ISO (formerly also called ASA):

• Box Speed ISO: the nominal film sensitivity rated by the manufacturer.
• Exposure Index (EI): the ISO value you actually use to calculate exposure while shooting; simply put, “the ISO you shoot at.”

They can be the same or different. For example, shooting ISO 400 box-speed film at EI 200 usually means intentional one-stop overexposure (and you may compensate with pull processing later—or not).

Recording EI helps you better reconstruct your original exposure intent and supports later development decisions and image review.

So LightLog supports recording both ISO and EI: ISO is written to standard EXIF fields, while EI is written to UserComment.

8) Further reading

• If you want to explore all EXIF tags, the ExifTool project website is an excellent resource: ExifTool Tag Names

Last updated: May 25, 2026

This document is based on LightLog feature design and metadata handling approaches as of the date above. As the app keeps evolving, some details may differ from the latest version. Please refer to the app itself for final behavior.