Why Dolby Vision and DaVinci Resolve trainers insist on full levels for HDR

“Rec. ITU-R BT.2100 specifies two different signal representations, “narrow” and “full”. Narrow range signal representations are traditionally used for television programme production. They provide headroom above the code value of the nominal peak (where the signal E′ > 1.0) and below zero light (where the signal E′ < 0.0) to accommodate signal overshoots and undershoots… Full range signal representations are more common in cinematic workflows. The movie industry has traditionally followed the computer graphics industry and placed zero light at digital code value “0”, and the code value of the nominal peak at the maximum code value for the given bit-depth. Full range signals do not, therefore, provide any headroom for signal overshoots or undershoots.

Signal overshoots and undershoots are produced by video processing techniques such as image re-sizing, filtering and compression, that are common in television production workflows… In order to maintain image fidelity, it is important that such overshoots and undershoots are not clipped. Any signal clipping introduces harmonic distortion, which makes the task of subsequent video compression or filtering even harder. Full range signals, which cannot accommodate signal overshoots and signal undershoots, are thus generally avoided in broadcasting systems… The full range representation for PQ signals may, however, be useful as it provides an incremental advantage against visibility of banding/contouring and for processing. Furthermore, because the range of PQ is so large, it is rare for content to contain pixel values near the extremes of the range. Signal overshoots are therefore less likely to exist.”


One thought on “Why Dolby Vision and DaVinci Resolve trainers insist on full levels for HDR

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  1. Jon, selection of the operational range between full or narrow should not be characterized as if it were an artist’s aesthetic choice pushed by trainers. The true grading space is always the 32 bit internal range of Resolve between 0 and 4,294,967,295. Narrow or full levels refer to the matching ranges for the source input/output (Prores=narrow, XAVC-I = full), and the system (tv=narrow, PC=full).

    If your output is full for a system expecting narrow, the above-blacks and below-whites end up in the over/undershoots range where they are clipped. Actual near blacks become (super)black, near whites become(super)white. This is perceived as excessive contrast with crushed blacks and blown whites.

    The reverse is true for a system expecting full when receiving narrow, blacks are shown as gray and whites are less than white, resulting in a flat, low contrast appearance.

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