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 color space defines the limits of color gamut, gamma and white point 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 color space you need to work in and deliver.
While HDR is sexy and more 4K HDR ready TV’s are being sold around the world, reference grade HDR monitoring is out of reach for most of us. So for now, I’m going to introduce you to the common video color space you’ll use for the web, mobile screens and SDR television.
Common Video Color Spaces
For the most part you only need to be concerned with one color space, and that’s the standard HDTV Rec. 709, or BT. 709.
sRGB is a color space originally created for CRT computer monitors, graphics and print. It is almost identical to the Rec. 709 video color space. It’s based on the same primaries and has basically the same gamut as Rec 709. sRGB has a non-linear gamma in order to approximate the response of CRT display technology.
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 much to do with video, except to know that Rec. 709 video will look fine on a sRGB computer display.
Rec. 709 is the recognized standard video color space for HDTV with a gamut almost identical to sRGB.
For broadcast 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 usually 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 projects. The Rec. 709 gamut is supported by all common display technologies across many devices.
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 specifications for UHD HDR. As far as color gamut, it covers a large percentage of the full 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 average user post workflows unless you are mastering for HDR delivery.
This is becoming more common for commercial high-end delivery, but not something the home freelance DP/colorist or enthusiast will be equipped to undertake for some time to come. The average consumer HDR television is not going to cut it as a reference display for post production. Some premium OLED HDR televisions can be calibrated for excellent Rec. 709 SDR reference monitoring, but not HDR.
Choosing The Right Video Color Space
The source camera files we typically deal with from a digital cinema camera provide at least 10-bit color depth and cover a native color gamut that far exceeds the requirements for DCI-specification, and in most cases covers or exceeds Rec. 2020.
Ideally you should be working in a wide gamut color space that encompasses all the expected output standards and have your monitoring calibrated to match.
If 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 for the best results. 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, and for web delivery this is usually fine when targeting Rec. 709.
I hope this has provided a basic understanding about color spaces, what they are, the common standards, and how you should be using them.
For a more in depth look at professional color management the following paper from www.cinematiccolor.com is well worth reading: Cinematic Color, From Your Monitor to the Big Screen