Based on the detailed technical analysis provided in your text, here is a structured summary of the key findings regarding sRGB profile variants, their technical integrity, and practical recommendations for workflow management.
The text highlights two specific variants found on color.org that differ from the standard sRGB definition:
- The "Black Scaled" Profile:
- Characteristics: Uses the standard 1024-point sRGB TRC but starts at
(0,0). However, it has a non-zero black point in its ICC tag. - Verdict: Faulty. The black point contradicts the tone curve.
- Status: Removed from the
color.orgwebsite.
- Characteristics: Uses the standard 1024-point sRGB TRC but starts at
- The "No Black Scaling" Profile:
- Characteristics: Uses a distorted 1024-point TRC starting at
(0, 819)(approx. value 3 on a 0-255 scale). It has a non-zero black point. - Verdict: Not a true sRGB profile. It lacks the proper sRGB tone curve.
- Consequences of Use (without Black Point Compensation):
- Shadows get lighter: When converting relative colorimetrically, shadow data is pushed into the profile's internal black point, causing loss of detail.
- Shadow Crushing: Converting back to a proper sRGB profile without compensation crushes shadows to zero (black).
- Color Shift (Absolute Intent): If white points differ and absolute colorimetric intent is used, neutral grays can shift dramatically (e.g., turning gray into blue).
- Current Status: Removed from the
color.orgwebsite due to these issues. - Exception: The ICC officially states this profile might be intended for monitors lacking a real profile (to simulate LCD behavior vs. CRT), but real monitor profiles are preferred.
- Characteristics: Uses a distorted 1024-point TRC starting at
A robust ICC RGB working space profile must meet two criteria: 1. Color-Balanced: When $R=G=B$, the resulting Lab values must be neutral ($a=0, b=0$). 2. Normalized: * $R=G=B=0 \rightarrow L^ab = (0, 0, 0)$ * $R=G=B=Max \rightarrow L^ab = (100, 0, 0)$
The text tested 5 groups of profiles using the tool xicclu.
BetaRGB Comparison: Even standard spaces like BetaRGB show tiny deviations ($< 0.003$), proving that perfect balancing is rare across the industry, though usually negligible for visual perception.
- Visibility of Errors: The deviations in "imperfect" profiles (Groups 2, 3, 4) are so small that unless you are performing extensive color space conversions plus high saturation, you likely won't see visible color differences.
- Software Limitations: Despite being capable of 16/32-bit handling, many software packages default to non-balanced, non-normalized built-in sRGB profiles, sacrificing potential accuracy.
- Workflow Strategy:
- For Untagged Images: Do not rely on the "Internet Standard" or "Built-in" profiles suggested by editing software.
- Assignment: Manually assign the ArgyllCMS sRGB profile (or the specific profile from your camera, e.g., Canon) to untagged files.
- Conversion: When converting between untagged files and a working space, ensure you use Relative Colorimetric intent.
- Avoid: Do not use the "no black scaling" or "black scaled"
color.orgprofiles unless you specifically understand the risks and are replacing a missing monitor profile.
While the industry is fractured by multiple sRGB variants (some perfectly balanced like ArgyllCMS, some slightly off, and some broken like the legacy color.org profiles), the differences are often mathematically minor and visually imperceptible for most users. However, for a rigorous digital darkroom workflow, managing color carefully by selecting a color-balanced and normalized profile (like the ArgyllCMS variant) is the superior approach. Be wary of "simplified" tone curves and always verify the intent (Relative vs. Absolute) during conversion to avoid crushing shadows or shifting colors.