HDR vs. SDR Contrast Ratios

Rory Gordon, Senior Colorist at ArsenalFX Color, during a presentation at a 2019 SMPTE conference entitled “Beyond Better Pixels: How HDR Perceptually and Emotionally Effects [sic] Storytelling”, used data gathered from her work as a colorist on over 35 episodes of HDR content to explore the psychological and emotional impact high dynamic range has on the viewer. In the course of her speech, Ms. Gordon spoke about the differences in contrast ratios between the SDR grade and the HDR trim pass on three shows (and three genres): a one-hour medical drama, a half-hour superhero comedy, and a one-hour spy thriller. It bears noting that, although targeting 1,000 nits for the HDR pass, the mean picture level was actually lower on all three shows compared to the SDR grade. As expected however, the overall contrast of the HDR deliverables increased. The graphics below demonstrate the marked difference in contrast ratios between the SDR and HDR grades, using measurements of the skin tone key and skin tone fill levels.

Upon examination of the contrast of the HDR trim pass, it was found that in some cases, both the key and fill sides increased; at other times, the key side increased while the fill side decreased; and at times (in very dark scenes), both the key and fill sides of the faces decreased – establishing the importance of trimming according to the program’s style, not just hitting nit targets.

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