Color Profile Information in Image Metadata

Color Space and ICC Profiles in Image Metadata

Color profile information determines how the numerical pixel values in an image translate to actual visible colors. Incorrect color profile handling can result in washed-out, oversaturated, or shifted colors.

EXIF ColorSpace Tag

The EXIF standard includes a ColorSpace tag (0xa001) with two common values:

• 1 = sRGB: The standard color space for web and consumer devices
• 65535 = Uncalibrated: Usually means Adobe RGB or a custom profile

This tag alone is insufficient for professional workflows — the actual ICC profile embedded in the file provides complete color information.

Common Color Spaces

Color Space	Gamut	Primary Use
sRGB	Standard (~35% of visible)	Web, social media, consumer prints
Adobe RGB	Wide (~50% of visible)	Print publishing, CMYK conversion
ProPhoto RGB	Very wide (~90% of visible)	Archival, HDR processing
Display P3	Wide (~46% of visible)	Apple devices, modern monitors
Rec. 2020	Ultra-wide	HDR video, future displays

ICC Profiles

ICC (International Color Consortium) profiles are embedded as binary data in image files. They define:

ICC Profile Structure:
├── Profile Header (128 bytes)
│   ├── Profile size
│   ├── Color space (RGB, CMYK, Lab)
│   ├── Profile connection space (XYZ or Lab)
│   ├── Rendering intent
│   └── White point (D50, D65)
├── Tag Table
│   ├── Red/Green/Blue TRC (Tone Reproduction Curves)
│   ├── Red/Green/Blue Colorant XYZ values
│   ├── Media white point
│   ├── Copyright
│   └── Profile description
└── Tag Data
    └── Actual curve and matrix data

Gamma and TRC

Each color profile defines a Tone Reproduction Curve (TRC) for each channel:

• sRGB: Uses a compound curve (linear segment + power function, approximately gamma 2.2)
• Adobe RGB: Uses gamma 2.2 exactly
• ProPhoto RGB: Uses gamma 1.8
• Linear: Gamma 1.0 (used in HDR and computational photography)

Color Space in Camera RAW

RAW files do not have a color space applied — they contain linear sensor data with the camera's spectral response. The color space is chosen during RAW processing:

1. Camera records raw sensor data (linear, camera-specific color space)
2. RAW processor applies a camera-to-XYZ matrix (camera calibration)
3. User selects output color space (sRGB, Adobe RGB, ProPhoto RGB)
4. Processor converts XYZ to output space and embeds ICC profile

Web Display Considerations

Browsers handle color profiles with varying degrees of correctness:

• Chrome/Edge: Color-managed for images with profiles (tag images and CSS)
• Firefox: Full color management for all content
• Safari: Full color management, Wide Color (P3) support

Images without an embedded profile are assumed to be sRGB. If an Adobe RGB image is displayed without its profile, reds and greens will appear desaturated.