Rec.709 (BT.709)

ITU-R BT.709 defines three parameters: color gamut, transfer function, and white point. The gamut covers 35.9% of the CIE 1931 visible spectrum — significantly smaller than DCI-P3 (45.5%) and P3-D65 used in HDR (also 45.5%). The D65 white point sits at 6500K on the Kelvin scale (x=0.3127, y=0.3290 in CIE xy coordinates). The transfer function uses a gamma of approximately 2.4 for reference monitoring in dim surround conditions (5 lux ambient), though the actual BT.709 OETF is a piecewise function with a linear segment near black and a 0.45 power function above 4.5% signal level. In DaVinci Resolve, setting your timeline color space to Rec.709 Gamma 2.4 tells the software to interpret and output values according to this curve. Every YouTube video, every Netflix SDR stream, every broadcast deliverable you have ever watched was mastered in Rec.709.

DCI-P3 and Rec.2020 offer wider gamuts. HDR delivery (HDR10, Dolby Vision) uses these larger spaces. But Rec.709 persists because the display ecosystem has not caught up. Most laptop screens, office monitors, and mobile devices are closer to sRGB (which shares the same gamut as Rec.709) than to P3. Delivering P3 content to an sRGB display means the gamut gets clipped or incorrectly mapped — colors shift, saturation drops, or both. The practical constraint: if your deliverable is web video, grading in P3 and converting down to Rec.709 introduces gamut mapping decisions you could have avoided by grading in the target space from the start. Grade in the delivery space. For HDR deliverables, use a P3 or Rec.2020 timeline with proper tone mapping. For SDR web delivery, stay in Rec.709. Trying to future-proof an SDR grade by working in P3 is a waste of time — the extra chromaticity gets thrown away on output. That said, if you are mastering for theatrical DCP or HDR streaming, P3 is the correct working space and Rec.709 becomes your SDR trim pass.