Improve metering

[natural-harmonia-gropius]

What I did?

• Convert linear values to perceptual luminance (PQ)
• Downscaling image to fixed size (512x288)
• Spatial filtering for image of metering (fast gaussian blur, default to 2 iterations)
• Get metered values (max)
• Temporal filtering for metered values (harmonic mean, default to 1/3 fps samples)

What does Dolby do?

视界·本色｜杜比视界全新 L1 元数据介绍

• Spatial filtering (downscaling, fixed resolution(?), 基于最大空间频率的滤波算法(?))
• Highlight processing (5 levels analysis tuning, from most to least highlight, default to balance, blurring(?)).
• Get values (in PQ, max: weighted maxRGB, avg: improved(?), min: minY)
• Working space (BT.2020)
• Three-segment spline curve.

What I want

• Reduce flickering
• Better black and white clipping, tm(w_in) == w_out, tm(b_in) == b_out
• Mid-grey adaptation, tm(m_in) == m_out