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Filmmaking Dictionary: Letter R / Rec.709 (BT.709)
Definition
Rec.709, formally ITU-R BT.709, is an international recommendation defining parameters for high-definition television production and programme exchange. In everyday post-production language, “Rec.709” often refers to its colour primaries and a conventional standard-dynamic-range viewing or delivery workflow.
The name is useful shorthand, but a complete delivery specification also needs such information as resolution, frame rate, codec, signal range and the intended transfer and display behaviour.
What the Colour Space Describes
The red, green and blue primaries define a colour gamut: the range of colours represented by combinations of those primaries. Rec.709 uses a D65 reference white. Its gamut is smaller than Rec.2020.
Gamut is separate from pixel count. A UHD file can carry imagery using Rec.709 colour parameters; increasing the raster from HD to UHD does not automatically make the image wide gamut or HDR.
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Rec.709 and Gamma
The recommendation includes an opto-electronic transfer function describing signal encoding. The reference display electro-optical transfer function used for HDTV studio work is specified separately in BT.1886. This is why a software menu may distinguish colour primaries from gamma or display transfer settings.
Do not assume that every option labelled “709” behaves identically. Camera viewing looks, output transforms, display profiles and export metadata can serve different purposes. Establish the intended signal path before changing settings to make one viewer match another.
Working with Log or RAW Material
Log-recorded or RAW-origin footage usually needs an appropriate interpretation and transform for the intended display. A technical transform maps the source into the target viewing space; creative grading determines the look within that workflow.
A camera’s monitoring LUT may affect only the viewing output, or it may be recorded into a selected output or file. Check the camera and recorder configuration. Applying a second conversion to an image already transformed can crush shadows, clip highlights or distort colour.
Delivery Checks
- Identify the source colour space and transfer characteristics correctly.
- Set the timeline and output transforms for the required delivery.
- Use a suitable calibrated viewing arrangement for critical decisions.
- Check signal levels, colour metadata and actual playback of the exported file.
- Keep an HDR version and an SDR conversion clearly identified when both are required.
For example, a log interview can be graded for an SDR Rec.709 master while retaining the original camera files for later versions. Merely changing a metadata label is not a substitute for a correctly managed colour conversion.
Related Terms
- Rec.2020 (BT.2020)
- LUT (Look-Up Table)
- Color Bars
- Quality Control (QC) in Post-Production
- ACES (Academy Color Encoding System)
Browse terms beginning with R or return to the filmmaking dictionary.