Color Space: Cinematography!

May 09 2022

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As art of cinematography evolved, lot of technical science was standardized, like Aspect Ratio, frame rate for exhibition to various platforms especially to theatres.

Color space is important technical color information standards for filming and exhibition, this topic got prominence after digital cinematography happened.

A color space is a defined range of colors.

Color space

A color space describes a specific, measurable, and fixed range of possible colors and luminance values. Its most basic practical function is to describe the capabilities of a capture or display device to reproduce color information.

A video color space defines RGB values a color component transfer function and the chromaticity of a white point. These values define how color information is encoded for a particular video standard. 

All video is to be watched and delivered  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.

Viewing Monitors and its pipeline should be calibrated for the color space of the video standard that you will deliver in.

Today, those fixed pipelines and workflows are a thing of the past. Source material can come from one or several of the dozens of available capture formats — iPhone, GoPro, Canon, Sony, RED, Alexa, 35mm, etc.—many of which themselves offer multiple choices of color space

On the delivery side, a given piece of content may need to be played in theaters, as well as on SDR and/or HDR TVs,  ever-changing list of mobile devices and VR sets.

Common Video Color Spaces

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

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.

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.

Rec.709 has a approx 40% of color gamut of visible colors

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

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.

Rec. 2020

A wide gamut color space encompassing approximately 75% of all visible colors.

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.

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.

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.

Color Management

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.

Having OTT platforms emerging into biggest viewing, now HDR color grade is preferred as a preferable delivery format.

Dolby vision uses hdr out a color space of rec. 2020.

What is BT.2020? The Newest Color Range Standard Maximizes 4K Video Quality  | BenQ Hong Kong

Article by

CJ Rajkumar

Author/ cinematographer

 

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