Colour Space (Rec.709 / Rec.2020 / DCI-P3)
Definition
A colour space, in video, is defined by a set of primaries, a white point and a transfer function, which together fix how signal values correspond to real colours. Rec.709 (ITU-R BT.709) is the HD and SDR standard. Rec.2020 (ITU-R BT.2020) is the wide-gamut container for UHD and HDR, used with ITU-R BT.2100, and few displays can reproduce it entirely. DCI-P3 (SMPTE RP 431-2), used in digital cinema, lies between the two, and its variant with a D65 white point (P3-D65) is often used for HDR mastering. Rec.709 and Rec.2020 both use the D65 white point. Content created in one space and displayed as if it were in another looks over- or undersaturated, with shifted hues.
In the field
Content is tagged and interpreted in the same colour space along the whole chain. Rec.709 content shown as Rec.2020 looks oversaturated and garish, because its narrow primaries are stretched to wide ones; Rec.2020 content shown as Rec.709 looks desaturated and washed out. The media server, the processor and the wall are set to one agreed space before content is graded.
Related lessons
Sources
- ITU-R BT.709 : primaires, point blanc D65 et fonction de transfert de la HD · itu.int
- ITU-R BT.2020 : primaires à large gamut et point blanc D65 de l'UHD · itu.int
- Wikipédia, DCI-P3 : SMPTE RP 431-2, variante P3-D65 (pointeur secondaire) · en.wikipedia.org
- Wikipédia, Rec. 2020 : conteneur UHD à large gamut, couverture comparée à Rec.709 et DCI-P3 (pointeur secondaire) · en.wikipedia.org
- SMPTE RP 431-2:2011, D-Cinema Quality: Reference Projector and Environment : projecteur de référence et gamut DCI-P3 · pub.smpte.org