光探所⦿ HDR NODE/EOTF TRANSFORM

• 官網測試素材下載：sonycine.com/testfootage/#
  – 攝影機特色介紹：SONY VENICE
  – 編碼介紹：X-OCN白皮書

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• 調光軟體：DaVinci Resolve 18.6.2
• 專案設定：
  – Color Management: DaVinci YRGB ／Rec.709(scene)
  – Sony Camera Raw decode: Full res-Resolve ／Camera metadata

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💡ABOUT HDR

先看看維基百科：https://en.wikipedia.org/wiki/Rec._2100

ITU-R Recommendation BT.2100, more commonly known by the abbreviations Rec. 2100 or BT.2100, introduced high-dynamic-range television (HDR-TV).

關於色彩空間 & EOTF：

• Rec. 2100 uses the same color primaries as Rec. 2020 which is a Wide Color Gamut.
• Rec. 2100 defines two sets of HDR transfer functions which are perceptual quantization (PQ) and hybrid log-gamma (HLG).

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那麼，什麼是PQ呢，感謝Nick Shaw編寫展示：ST.2084 (PQ)

ST.2084 is an absolute encoding of display luminance developed by Dolby and standardised by SMPTE as ST 2084:2014. It is commonly referred to as PQ, and is specified in ITU-R BT.2100.

BT.2100 specifies Rec.2020 primaries for use with PQ, although some delivery specs (e.g. Netflix) ask for PQ with P3-D65 primaries. In fact frequently Rec.2020 PQ image data is constrained to P3-D65, with Rec.2020 used as a “half pint in a pint glass” container, and many delivery specs mandate this.

由於目前尚未有螢幕完全覆蓋支援100% Rec.2020 廣色域，因此像Netflix大部分的影音串流平台，訂定的HDR影片交付規格，Colorimetry 標準為 P3-D65/SMPTE ST 2084 (PQ)，較好地去適應消費端電視、手機、平板等螢幕面板的顯示能力。

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💡 ABOUT OETF /EOTF /OOTF

ITU這麼說的：詳見PDF Annex 1 (informative) — The relationship between the OETF, the EOTF and the OOTF , page 11.

In general the OOTF is a concatenation of the OETF, artistic adjustments, and the EOTF.

OETF/光電傳遞函數: 攝影機傳感器捕獲的畫面。以Arri舉例，LogC就是一種OETF，將場景光線以線性模式 (linear scene light) 轉換為影像信號數據 (video signal)。

EOTF/電光傳遞函數: 顯示器將OETF影像信號數據，解碼轉換成自身能顯示的螢幕亮度。以 SDR舉例，Gamma 2.4 就是一種 EOTF. 以 HDR 舉例，PQ 也是EOTF.

OOTF/光學傳遞函數: 一般來說，就是OETF+EOTF的顯示結果（完畢）。

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如何在SDR調光專案(Rec.709/scene)，實現HDR調光模式？

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◓ Node 01

• Node勾選 HDR Mode，使用 Primary Color Tools 執行色彩平衡或校正
• Node Color Space: DaVinci Wide Gamut

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◓ Node 02: CST OFX (input)

• OFX Color Space: 將設定從 P3-DCI(大色域)轉為 Rec.709(小色域)，是為了得到色濃度強化的影像 (Color Space Enhanced).
  
  小色域/Input to 大色域/Output = desaturated image
大色域/Input to 小色域/Output = saturated image
  
  
• OFX Color Gamma: 將Sony Raw(SLog3)以DaVinci Intermediate的模式，轉移至HDR EOTF-Rec.2100 ST2084 (Scene)
  
  
• Node Gamma: Rec.2100 ST2084 (Scene)

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►官方Monitor LUT下載位址: s709 cubes
►測試素材使用的 Monitor LUT: SL3SG3Cto709 (Rec.709 )

• Node Color Space: DaVinci Wide Gamut
• Node Gamma: Rec.709

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◓ Node 04: Desaturated Highlight

• 使用 Lum VS Sat 曲線，平衡經過調光，高光區域可能產生的溢色

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◓ Node 05: CST OFX (output)

• 使用 CST OFX，需要時可再次執行 Color Space/Gamma Enhanced.
  
  小色域/Input to 大色域/Output = desaturated image
大色域/Input to 小色域/Output = saturated image
小Gamma/Input to 大Gamma/Output = low-contrast image
大Gamma/Input to 小Gamma/Output = high-contrast image
  
  
• 使用 CST OFX，執行Saturation Compression，抑制調光後的溢色

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我的應用題：《誰是被害者》第二季

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“The purest and most thoughtful minds are those which love color the most.”
―John Ruskin, The Stones of Venice

關於面對調光素材，是聽到拍攝器材是SONY，器官就開始翻江倒海。2023與之再度對決，被害者遊戲，第二回合。

擂台對面站著SONY VENICE兄弟，一代與二代。掛載Scorpio與Cooke變形鏡頭，柔柔濾鏡Pro-Mist，編碼X-OCN，雙組，四機。

至於我是如何度過鼻青臉腫，完成《誰是被害者》第二季，感謝 DaVinci Resolve 永遠為我指路。在SDR專案實現HDR調光模式，多麼迷人。仍然有各種可能，各種實驗，這不是絕對的調光方法。

這段沒有海圖的航行，由製作被害者遊戲第一季起頭，第二季到了頭。翻開工作日誌，1700多個日子，物換星移，多麼迷幻。感恩的心。

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倉庫番 #映# 實驗事 
coz i am a colorist
ARIEL CHENG

#SHOWREEL
#2024