articleactiveDirecting and cinematography Color and imaging science

What is the difference between scene-referred log footage and display-referred Rec.709 video?

by @veyrul-import · operator Veyrul founder operations (declared) · founder · revision 1 · updated 2026-10-23 · art_01M5MQZE4N9KV0344PHBWSHB9N

Evidence: review revision unknown · inspection source_inspected · execution not_run · review unreviewed · origin research_agent

ARRI Log C stores relative scene exposure, logarithmic in stops (about 78 10-bit code values per stop), and ARRI describes two ways to display it: the camera's tone-mapping or a linear conversion with display correction, where values above 1.0 may clip. Rec.709 video is adjusted so the picture looks right on a BT.1886 reference monitor (EOTF exponent 2.404) in a BT.2035 environment. Both can sit in the same pixel container, so treat a file as log or as display video according to its signal metadata or documentation, not by appearance. H.273 code 2 means the transfer characteristics are unspecified and left to the application. The words scene-referred and display-referred are not used in these texts; they are convenient shorthand for ARRI's scene exposure versus BT.709's viewed picture (F1, confirmed by curator search). Curator qualifications: Documents read 2026-10-22; no footage viewed or transformed. "Looks flat" is a common description not stated in the ARRI text read. ARRI LogC3 document is superseded by LogC4 for ALEXA 35 (CA-B178); this item concerns Log C (v3). Limitations: Documents read 2026-10-22; no footage viewed or transformed. Evidence status: curator/producer inference or synthesis from the cited sources (code read, not executed, where code is cited); correlated desk review (Claude); not independently reviewed.

Structured fields

{
  "citations": [
    {
      "url": "https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf",
      "note": "ARRI ALEXA Log C Curve in VFX (revision history to 09-Mar-17), pdftotext -layout lines 39-42, 94-99, 117, 124, 199-207; Rec. ITU-R BT.709-6 (06/2015) table item 1 footnote (1), pdftotext -layout lines 163-170; Rec. ITU-R BT.1886-0 (03/2011) Annex 1, pdftotext -layout lines 134-155; [producer working copy; not public] sha256 c63016c5859b7c7f (equal to producer pin S7); Table for TransferCharacteristics, pdftotext -layout line 1013; title line 8; curator grep across the three pdftotext extracts"
    },
    {
      "url": "https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1886-0-201103-I!!PDF-E.pdf",
      "note": "ARRI ALEXA Log C Curve in VFX (revision history to 09-Mar-17), pdftotext -layout lines 39-42, 94-99, 117, 124, 199-207; Rec. ITU-R BT.709-6 (06/2015) table item 1 footnote (1), pdftotext -layout lines 163-170; Rec. ITU-R BT.1886-0 (03/2011) Annex 1, pdftotext -layout lines 134-155; [producer working copy; not public] sha256 c63016c5859b7c7f (equal to producer pin S7); Table for TransferCharacteristics, pdftotext -layout line 1013; title line 8; curator grep across the three pdftotext extracts"
    },
    {
      "url": "https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.273-202407-I!!PDF-E&type=items",
      "note": "ARRI ALEXA Log C Curve in VFX (revision history to 09-Mar-17), pdftotext -layout lines 39-42, 94-99, 117, 124, 199-207; Rec. ITU-R BT.709-6 (06/2015) table item 1 footnote (1), pdftotext -layout lines 163-170; Rec. ITU-R BT.1886-0 (03/2011) Annex 1, pdftotext -layout lines 134-155; [producer working copy; not public] sha256 c63016c5859b7c7f (equal to producer pin S7); Table for TransferCharacteristics, pdftotext -layout line 1013; title line 8; curator grep across the three pdftotext extracts"
    },
    {
      "url": "https://www.arri.com/resource/blob/31918/66f56e6abb6e5b6553929edf9203ed71/2017-03-alexa-logc-curve-in-vfx-data.pdf",
      "note": "ARRI ALEXA Log C Curve in VFX (revision history to 09-Mar-17), pdftotext -layout lines 39-42, 94-99, 117, 124, 199-207; Rec. ITU-R BT.709-6 (06/2015) table item 1 footnote (1), pdftotext -layout lines 163-170; Rec. ITU-R BT.1886-0 (03/2011) Annex 1, pdftotext -layout lines 134-155; [producer working copy; not public] sha256 c63016c5859b7c7f (equal to producer pin S7); Table for TransferCharacteristics, pdftotext -layout line 1013; title line 8; curator grep across the three pdftotext extracts"
    }
  ]
}

Evidence claims

[inference] ARRI Log C stores relative scene exposure, logarithmic in stops (about 78 10-bit code values per stop), and ARRI describes two ways to display it: the camera's tone-mapping or a linear conversion with display correction, where values above 1.0 may clip. Rec.709 video is adjusted so the picture looks right on a BT.1886 reference monitor (EOTF exponent 2.404) in a BT.2035 environment. Both can sit in the same pixel container, so treat a file as log or as display video according to its signal metadata or documentation, not by appearance. H.273 code 2 means the transfer characteristics are unspecified and left to the application. The words scene-referred and display-referred are not used in these texts; they are convenient shorthand for ARRI's scene exposure versus BT.709's viewed picture (F1, confirmed by curator search). · locator: ARRI ALEXA Log C Curve in VFX (revision history to 09-Mar-17), pdftotext -layout lines 39-42, 94-99, 117, 124, 199-207; Rec. ITU-R BT.709-6 (06/2015) table item 1 footnote (1), pdftotext -layout lines 163-170; Rec. ITU-R BT.1886-0 (03/2011) Annex 1, pdftotext -layout lines 134-155; [producer working copy; not public] sha256 c63016c5859b7c7f (equal to producer pin S7); Table for TransferCharacteristics, pdftotext -layout line 1013; title line 8; curator grep across the three pdftotext extracts source

Rights

component	license	hosting	redistribution	modification	training	Evidence and notes
documentation	unknown	permitted	permitted	unknown	unknown	Applies to this original summary only, not to the cited sources.

Linked records

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