How do you choose the right video color space for your project? I want to take you through a few basic color spaces and their applications.
A video color space defines RGB chromaticities that together determine a color gamut, a color component transfer function (often referred to using a confusing and unhelpful but common term “gamma”) and the chromaticity of a white point. These values define how color information is encoded for a particular video standard. All video is intended to be delivered and watched on some kind of display device. This could be a television, PC or laptop display, tablet, phone, cinema projector, or HDR television. How your video content will be consumed determines the video color space you need to create in and deliver.
Your monitoring pipeline should be calibrated for the color space of the video standard that you will deliver in.
While HDR is sexy and 4K HDR TV’s are in many homes around the world, reference grade HDR monitoring is out of reach for most of us. So, I’m going to introduce you to the most common video color spaces you’ll hear about, and the one you’ll use for the web, mobile screens and broadcast television deliverables.
Common Video Color Spaces
If you’re not sure exactly what a video color space is, I explain this in my article What is A Video Color Space? For the most part you still only need to be concerned with one color space, and that’s the standard HDTV Rec. 709, or ITU-R BT. 709.
sRGB is a display referred color space originally created for CRT computer monitors, but has become standardized for graphics and print. It is almost identical to the Rec. 709 video color space. It’s based on the same primaries and has the same gamut as Rec. 709 but specifies a different transfer function.
sRGB is still the standard for computer imaging, most consumer to mid level photo cameras and home printers. For professional printing and pre-press purposes Adobe RGB is often used which has an extended gamut that can be reproduced with professional CMYK printing. sRGB doesn’t have anything to do with video in the context of broadcast standards, except to know that for the most part Rec. 709 video will look fine on a sRGB computer display. There might be a slight difference in brightness due to the difference in transfer function.
Rec. 709 (ITU-R BT. 709)
Rec. 709 is the standard camera encoding color space for HDTV with a gamut identical to sRGB. As previously stated, sRGB and Rec. 709 primaries share the same chromaticity values (and therefore the same gamut). However, Rec. 709 differs slightly in its encoding transfer function, and doesn’t actually specify an inverse transfer function for display.
For broadcast encoding, it is defined in 8-bit color depth (values between 0 and 255) where black is level 16, and white is level 235. These are often referred to as “video levels”.
In the case of 10-bit color depth which is common for post production, full range levels are between 0 and 1023, but the final output is mapped to broadcast standard 8-bit 16-235 when creating common deliverables.
Rec. 709 is by far the most common working and delivery color space for most video projects. If you’re creating video for broadcast delivery, or that will be consumed online, then Rec. 709 is most likely what you need to work and monitor in. The Rec. 709 gamut is supported by all common display technologies across many devices. Most computer video players know how to deal with Rec. 709 encoded video, and can display it correctly on an sRGB computer display.
DCI-P3 is a wide gamut video color space introduced by SMPTE for digital cinema projection. It is designed to closely match the full gamut of color motion picture film.
It is generally not a consumer standard and is mostly used for content destined for digital theatrical projection. However, notably Apple have adopted P3 color across many device displays, and the ability to capture photo and video in the P3 color space since iOS10.
Most professional reference monitors are able to display the full DCI P3 gamut.
You will often see a white point specified along with the color space, such as P3 D55, P3 D61 or P3 D65. The D number indicates the target white color temperature given in degrees Kelvin. D55 is 5500K, D61 is 6100K, D65 is 6500K, and the DCI standard white point is 6300K.
Rec. 2020 defines the color specifications for UHD HDR. As far as color gamut, it covers a large percentage of the full CIE XYZ color space. The standard defines 10-bit or 12-bit color depth. A few display technologies are fully Rec. 2020 compliant but as yet, it is not a common video color space to be working in for the average video creator.
HDR finishing is becoming more common for commercial high-end delivery, but not something the home freelance DP/colorist or video enthusiast will be equipped to undertake for some time to come. The average consumer HDR television does not meet the requirements as a reference display for post production. Some premium OLED HDR televisions such as the LG C9 and LG CX can be calibrated for excellent Rec. 709 SDR reference monitoring, but should not be used for HDR reference.
Choosing The Right Video Color Space
The source camera files from any digital cinema camera provide images encoded at high color bit depth with a native color gamut that far exceeds the requirements for DCI-specification, and in most cases meets or exceeds Rec. 2020.
Ideally, you should be working in a sufficiently wide gamut color space to encompass all the expected output standards you need to deliver and have your monitoring calibrated to match.
If theatrical digital cinema delivery is one of the requirements, you should work in DCI-P3 using a calibrated DCI-spec projector, or monitor that covers the DCI-P3 gamut.
If HD broadcast delivery is the widest gamut color space expected, or computer desktop / mobile / web at any resolution, you should work in Rec. 709.
Whatever color space you are working in, implementing professional color management at each step in your post monitoring pipeline is important. This means setting up your color grading working environment properly and calibrating all your displays.
That said, many of us have to make do as best we can with a consumer monitor or laptop screen. To be perfectly honest, for web delivery this is usually fine when targeting Rec. 709 as long as you’re using a high quality display. However, it’s best to avoid grading to a computer desktop GUI display because there are so many color management variables from OS, to software that are outside of your control.
I’ve compiled a guide to building your own color managed and calibrated monitoring pipeline based around the excellent LG OLED TV’s. They can be perfectly calibrated for Rec. 709 color correction and grading work.
You can add precision calibrated monitoring to your Resolve system for only $2200 – $3000 depending on whether you need to monitor in HD or UHD 4K. Note that in both cases I’m talking about Rec. 709 SDR use only.
I hope this has provided a basic understanding about video color spaces, what they are, the common standards, and how you should be using them.
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