The letter

One letter a week, starting soon.

The week's signal, what the makers shipped and what the reviewers found, and the editor's note. No tracking, no ads, nothing else.

We keep your address, your language and the date you joined, nothing else. Every letter has a one-click unsubscribe link that deletes the record.
Video basics3 min read

LESSON 94

Colour spaces: Rec.709, Rec.2020, ACES

Which colours a signal can carry.

IN THIS LESSON

  1. What a colour space defines
  2. Rec.709
  3. Rec.2020
  4. ACES
  5. Practice: matching space to delivery

What a colour space defines

A colour space sets which red, green and blue primaries a signal uses, where its white point sits, and how brightness is encoded. Two files with the same numbers can show different colours if they belong to different spaces, which is why colour management exists. For video the spaces are set by standards bodies: the International Telecommunication Union for television, and the Academy of Motion Picture Arts and Sciences for its own film workflow. Knowing which one your footage and your delivery use avoids washed-out or oversaturated surprises.

Rec.709

ITU-R Recommendation BT.709, usually called Rec.709, is the standard for high-definition television. It fixes a 1920 by 1080 picture in 16:9 and lists frame rates that include 24, 23.976, 25, 30 and their interlaced forms, along with the colour encoding. Its colour range is almost the same as older standard-definition television and covers about 35.9 percent of the CIE 1931 colour space. It is still the default for HD broadcast and HD Blu-ray, and most web video is graded to it.

Rec.2020

Rec.2020, first published in 2012, defines ultra-high-definition television: 3840 by 2160 and 7680 by 4320 pictures, progressive frame rates from 23.976 up to 120, and 10 or 12 bits per sample. Its primaries sit on the edge of the visible spectrum, so it can show many colours Rec.709 cannot. No consumer screen yet shows all of it; in 2015 NHK showed a laser-lit LCD covering 98 percent. Rec.2100 extends the same primaries to high dynamic range. For most working film-makers today, Rec.2020 matters as the container used for UHD and HDR delivery, even when the actual grade stays inside a smaller range of colours.

ACES

The Academy Color Encoding System, ACES, is a colour workflow created under the Academy. It defines its own very wide primaries and a white point near 6000 kelvin, and most ACES files use 16-bit half-float OpenEXR, enough for about 30 stops of scene information. Input transforms bring each camera into ACES, and output transforms render for each display. Version 1.0 came out in December 2014, and parts are standardised by SMPTE. Its purpose is to let footage from many cameras meet in one consistent pipeline.

Practice: matching space to delivery

This is working practice. Set your editor's timeline to the space you will deliver in, usually Rec.709 for web and HD. Tag your source clips correctly, so log or wide-gamut footage is converted rather than displayed as if it were already 709. Use ACES or a similar managed pipeline when footage comes from several camera brands or will be delivered in both SDR and HDR. Grade on a monitor that can actually show the space you are grading for. If you cannot, stay in Rec.709 and keep it simple.

Try it today

  1. 01Look up which colour space your camera records in each picture profile.
  2. 02Open your editor's project settings and find the timeline colour space.
  3. 03Import one log clip and check how the editor interprets it.
  4. 04Set the right input transform and compare before and after.
  5. 05Write the delivery space on the project's first page.