Field Naming Differences: Perl vs Rust

Overview

exiftool-rs uses structured field names with prefixes to indicate the metadata source, while Perl ExifTool uses simplified "friendly" names. The actual data extracted is identical.

Naming Patterns

1. Space Removal

Perl uses spaces in field names, Rust uses camelCase or concatenation:

• Bits Per Sample → BitsPerSample
• Image Width → ImageWidth
• Strip Byte Counts → StripByteCounts

2. Prefixes

Rust adds prefixes to show metadata source:

JPEG/TIFF Prefixes

• IFD0: - Main image metadata
• ExifIFD: - EXIF-specific data
• XMP-dc: - XMP Dublin Core
• XMP-xmp: - XMP basic schema

Examples:

Perl: Make
Rust: IFD0:Make

Perl: Creator
Rust: XMP-xmp:Creator

Perl: Color Space
Rust: ExifIFD:ColorSpace

PNG Prefixes

• PNG: - PNG chunk metadata
• PNG-pHYs: - Physical pixel dimensions
• PNG:tEXt: - Text metadata chunks
• IFD0: - Embedded EXIF metadata

Examples:

Perl: Image Width
Rust: PNG:ImageWidth

Perl: Pixels Per Unit X
Rust: PNG-pHYs:PixelsPerUnitX

Perl: Datecreate
Rust: PNG:tEXt:date:create

PDF Prefixes

• PDF: - PDF document metadata
• Profile: - ICC color profile data

Examples:

Perl: PDF Version
Rust: PDF:PDFVersion

Perl: Profile Description
Rust: Profile:ProfileDescription

MP4/QuickTime Prefixes

• QuickTime: - QuickTime container metadata
• ItemList: - Metadata item list (user data)
• UserData: - User data atoms

Examples:

Perl: Major Brand
Rust: QuickTime:MajorBrand

Perl: Artist
Rust: ItemList:Artist

3. Friendly Name Differences

Some fields have completely different names:

Perl ExifTool	exiftool-rs	Notes
Camera Model Name	Model	Perl adds "Camera" prefix
Primary Chromaticities	PrimaryChromaticities	Space removed
Photometric Interpretation	PhotometricInterpretation	Space removed
Y Cb Cr Positioning	YCbCrPositioning	Space removed

Computed Fields (Perl Only)

These fields are NOT in exiftool-rs because they're computed from other metadata:

Image Dimensions

• Image Size - Computed as "Width×Height" (e.g., "800×600")
• Megapixels - Computed as (Width × Height) / 1,000,000

Both Width and Height are available separately in Rust.

Video Fields

• Avg Bitrate - Computed as File Size / Duration

Diagnostic Fields

• Warning - Validation messages (e.g., "Text/EXIF chunk(s) found after PNG IDAT")

Internal Metadata

• Exif Byte Order - Indicates little-endian vs big-endian encoding
• File Type, File Type Extension, MIME Type - File classification

Quick Reference: Common Fields

JPEG/TIFF

Perl                    → Rust
----------------------------------------
Make                    → IFD0:Make
Camera Model Name       → IFD0:Model
Orientation             → IFD0:Orientation
X Resolution            → IFD0:XResolution
Y Resolution            → IFD0:YResolution
Resolution Unit         → IFD0:ResolutionUnit
Artist                  → IFD0:Artist
Date/Time Original      → ExifIFD:DateTimeOriginal
Color Space             → ExifIFD:ColorSpace
Exif Version            → ExifIFD:ExifVersion

PNG

Perl                    → Rust
----------------------------------------
Image Width             → PNG:ImageWidth
Image Height            → PNG:ImageHeight
Bit Depth               → PNG:BitDepth
Color Type              → PNG:ColorType
Compression             → PNG:Compression
Interlace               → PNG:Interlace
Modify Date             → PNG:ModifyDate

PDF

Perl                    → Rust
----------------------------------------
PDF Version             → PDF:PDFVersion
Page Count              → PDF:PageCount
Producer                → PDF:Producer
Create Date             → PDF:CreateDate
Modify Date             → PDF:ModifyDate
Linearized              → PDF:Linearized

MP4/QuickTime

Perl                    → Rust
----------------------------------------
Major Brand             → QuickTime:MajorBrand
Compatible Brands       → QuickTime:CompatibleBrands
Duration                → QuickTime:Duration
Time Scale              → QuickTime:TimeScale
Title                   → ItemList:Title
Artist                  → ItemList:Artist
Album                   → ItemList:Album
Genre                   → ItemList:Genre
Copyright               → ItemList:Copyright

Benefits of Rust Naming Convention

1. Source Clarity: Immediately know where metadata came from (IFD0, EXIF, XMP, etc.)
2. Namespace Prevention: Avoid conflicts when same field name exists in multiple sources
3. Programmatic Parsing: Easier to filter/group by prefix in code
4. Standard Compliance: Matches actual metadata structure specifications

Backward Compatibility

If you have scripts expecting Perl field names, you can:

1. Strip prefixes: IFD0:Make → Make
2. Add friendly aliases in your application layer
3. Use the raw field name for lookups, Rust will find it