tonenumber

Tonенumber is a proposed metric used in experimental digital media processing to quantify the overall tonal content of a signal, image region, or scene as a single numeric value. Its intent is to provide a comparable index across different media and processing pipelines, enabling adaptive techniques like compression, rendering, and grading to respond to tonal requirements.

Calculation and interpretation: In audio, tonenumber is typically derived from spectral characteristics of the signal, incorporating factors such as the spectral centroid, dynamic range, harmonic content, and perceived brightness. It is often normalized to a 0–100 scale, where lower values indicate flatter, less dynamic content and higher values indicate richer, more complex harmonic structure. In images, it may be computed from the luminance distribution, local contrast, and colorfulness, compressing the tonal distribution of a region into a single figure that correlates with perceived brightness range and contrast.

Development and status: There is no universal standard for tonenumber. Different researchers and software packages implement their own versions with varying weightings and ranges. It remains mainly within experimental or research contexts rather than a widely adopted industry metric.

Applications and limitations: Tonenumber can support adaptive tone-mapping, exposure adjustments in batch processing, and grading decisions in video production. However, the lack of standardization and the subjective nature of perceived tone are major limitations; tonenumber should be used alongside other perceptual metrics and context-specific considerations.

See also: Dynamic range, tonal balance, histogram, perceptual metrics, tone mapping.