“…Visual attributes are semantic properties of objects (e.g., "fuzzy", "plastic") that serve as a middle ground between low-level features (e.g., color, texture) and high-level categories. Attributes (or "concepts", their counterpart in multimedia retrieval) are known to provide an effective representation for image search [15,10,20,22,4,8,25,7], especially since they permit content-based keyword queries [10,22,7]. While often treated as categorical ("is smiling" vs. "is not smiling"), attributes can more generally be modeled as continuous or relative properties ("is smiling more than X") [16,21].…”