By Carlos Medina, Audiovisual Technology Expert and Advisor

Color on TV is one of the great allies to produce more attractive content, achieve unforgettable visual experiences and, therefore, generate more emotion and involvement among viewers. But has it always been that way? Have we reached the limits of technology when it comes to information flow with color images?

The answer to both questions is the same one: NO. We are all aware of the fact that the first images that we were able to capture, store, modify and disseminate were in B/W (in a broader sense, images with a grayscale from white to black), both in the field of photography and in the cinematographic field, including the television environment.

Color television arose on a timeline between the 1960s and 1980s, when most of the world’s viewers began to receive color images on their TV sets. Before those dates, what was happening were first technical decisions, tests and a real battle between TV companies to be first in the race towards color TV.

Color technology has been approving and applying new processes, codifications, norms and standards. In this long journey of changes and breakthroughs, two moments were key in the field of TV:

– The beginnings of color broadcasting with backward compatibility with monochromatic (B/W) signals. It is the birth of the first standards, the initial tests and broadcasts that were authorized in different territories all over the world. This was the case with NTSC (acronym for National Television System Committee) in the US from 1953; and in Europe with the PAL standard (Phase Alternate Line) and/or SECAM (Séquentiel Couleur à Mémoire, in French). These three are what we know as TV color coding systems.

– The revolution of the digitization of the TV signal flow, leaving the problems and considerations of analog video signals well behind. This digitization is allowing us to achieve improvements in color both in capture devices and in viewing or monitoring equipment, and, above all, through better control management within the color signal broadcast/reception processes.

The international standard for digital encoding of video signals into components was ITU-R 601, which defined the technical specifications for the Y (luminance) components and the R-Y and B-Y color components. This standard set out the way to full digitization in the TV broadcast environment.

Let’s try to understand what is going on with color at present in the television industry. For this, it is necessary to have some notions about color and its application in TV very clear.

A first approximation to what color is can be obtained from the definition: sensation produced by the light rays that impress the visual organs based on the wavelength.

This sensation is possible because of the properties of our sight -of the human eye- to be able to capture certain wavelengths, specifically those that we call the ‘visible spectrum’ (region of the electromagnetic spectrum that the human eye is capable of perceiving). After research and studies in regard to this matter, we can say that the human being has specialized photoreceptor cells -the rods and cones- which are found in the retina and are responsible for our vision. Specifically, cones give us the perception of color because they have the ability to detect the different wavelengths of light, specifically those classified as red (L cone), blue (S cone) and green (M cone).

Now is the time to ask how color is generated when artificial devices created by humans take the spotlight and what they have to do both in the way of producing color and when it comes to viewing or enjoying it.

In this article about color, human vision and television are closely linked. The starting point: wavelengths R (Red), G (Green) and B (Blue). This is commonly known as RGB.

It is also necessary to delve into color modes, which simply indicate us how to achieve a color gamut. There are two modes: additive synthesis and subtractive synthesis. Both human vision and television work under additive synthesis, that is, obtaining a color or a color gamut from the sum of the color components, both through the primary RGB colors and by means of the secondary ones: cyan (C), magenta (M) and yellow (Y).

Once these two modes have been identified, we approach what we know as color models, which are the different ways of formulating colors under parameters and/or numerical values. Thus, we find the RGB model, the CMYK model, the Color Lab model, HSB or HSL, among others.

In order to make it easier to perceive the different color models, some scholars proposed different systems of representation: Newton’s Color Circle (1704); Goethe’s Color Wheel (1810); the dodecagrams or colored stars by Charles Blanc (1867); Wilhelm Ostwald’s Double Cone (1853-1932); Albert Munsell’s Solid (1858–1918), the cube by Alfredo Hickethier, or the CIE (Commission Internationale de l’Eclairage) triangle in 1931, among others.

Worth highlighting is CIE1931 triangle, also known as the CIE1931 chromaticity space, which characterizes colors by means of a luminance parameter Y and two color coordinates X and Y that specify a point within that diagram. This representation system was based  on  a  series  of  experiments  conducted in the late 1920s by W. David  Wright  and  John Guild;  their experimental results were included in the CIE RGB specification, from which the 1931 specification was derived.

Under the RGB model, which obviously works with additive synthesis and is common to all capture devices (cameras), display devices (monitors and televisions) and projection (projectors), we ask ourselves a simple question: is the same color range represented in all instances? Obviously NOT.

We all have memories that in a given image the color looks different depending on which camera has made the capture and where we see it displayed. These differences are usually based on the color space of each particular device and equipment involved in the workflow within the TV environment.

A color space is simply the range or set of colors that an image can display on a particular device. There are many different color spaces, also known as color gamuts. So, how many are there?

There can be as many color spaces as there are equipment and devices in different production environments (analog/digital); the issue here is that in order to achieve proper control in color management we have to apply different norms or standards throughout the workflow.

In the broadcast television environment, there have been and there are currently some major standards, such as:

– ITU-R BT.601 and SMPTE-C primary colors: This mode is designed for controlled-view environments established by ITU-R BT.2035. The SMPTE-C (Society of Motion Picture and Television Engineers) put them in place for standard definition content (SDTV) in the US and in most countries where NTSC had been implemented.

– ITU-R BT.601 and EBU tech 3213 primary colors: This mode is designed for controlled-view environments laid down by EBU (European Broadcasting Union).

– Rec. 609 (ITU-R BT.709): This digital standard includes the color spaces for NTSC, PAL and SECAM SDTV analog formats.

– Rec. 709 (ITU-R BT.709): It is the color space for HDTV with Standard Dynamic Range (SDR). Released in 1990.

– Rec. 2020 (ITU-R BT.2020): It is the color space for UHDTV (4K TV) with Standard Dynamic Range (SDR). Released in 2012.

– BT.2100: ITU* published in 2016 this recommendation to include HDR in its BT.2020 specifications.

(*) ITU is the United Nations specialized agency for information and communication technologies (ICT). Founded in 1865, its objectives are to carry out technical studies, answer practical questions and offer technical recommendations.

As a general principle, the wider the color space that the standard has, the more colors and greater realism the resulting image will feature and, therefore, the more we will be able to enjoy the contents. But to make this possible at all times we have to perform a correct color management and proper device calibration. For example, the BT-2020 color standard allows to show about 3/4 of the visible color spectrum; while the BT.709 standard only displays 30% of the spectrum offered by the new BT.2020 standard.

What about digital cinema? Does it have its own color space? That’s right. Digital cinematography is making its own decisions and designing its own standards in order to offer a quality product in many aspects. In this specific case, it is the DCI-P3 color space (part of the SMPTE RP 431-2 standard on “Digital cinema quality – Projector and reference environment”).

DCI-P3 color space is not as broad as that of the BT-2020 standard. Therefore, in order to ensure future compatibility in terms of color, a new wider space has been defined that offers greater flexibility for color spectrum coding: the Academy Color Encoding System (ACES).

1865, its objectives are to carry out technical studies, answer practical questions and offer technical recommendations.

The trend for achieving efficient color management is to work on the post-production / grading of projects in ACES. In this way, a master file in ACES is obtained from which the necessary copies can be made in BT-2020, DCI-P3 or BT-709.

Under the CIE YXZ 1931 color rendering system, the Rec.2020 color space standard covers 75.8%; the DCI-P3 color space, 53.6%; the Adobe RGB color space encompasses 52.1%; and the Rec.709 color space comprises 35.9%.

Before finishing this article, it is convenient to keep in mind some technical parameters that will greatly define the color values with which we work in the digital environment of today’s television such as: the type of video signal, the type of subsampling for the color components, the bit depth or quantification of color (recommending a high bit depth/pixel –High Bit Depth- HBD), the type of codec and video format… and, also, the workflows under HDR (High Dynamic Range).

Color in the audiovisual field is formed / worked on from the very first decisions made during pre-production, such as the choice of camera type and recording form (with logarithmic curves, for example),the processes involved in filming and post-production / grading or the completion of the audiovisual product with the mastering.

Broadcast television for today’s viewers is a television under the  Rec.709 (ITU-R BT.709) color space, which takes us to what is known as an extended color space: Wide Color Gamut (WCG). But this is only the beginning, as novelties and innovations must continue to arrive that by far expand what we understand by color and, above all. allow enjoying other types of content (UHDTV / 4K TV – HDR – Rec. 2020).

The success of color for broadcast TV is not completely guaranteed so we must embrace a threefold commitment:

– Professional workflows between the different color spaces, looks, LUTs, lighting techniques… to offer attractive content at all stages in audiovisual production.

– Visual education for viewers that allows a better assessment and acceptance of the new color that will fill their TV screens. Also, training as a user to know how to calibrate their equipment, automate visual results and configure the “proprietary” color management systems provided by manufacturers of screens, TV sets and monitors.

– New presentation and projection devices that easily include new color spaces, from Rec.709 (ITU-R BT.709) to DCI-P3 and also ITU-R BT.2020 / BT.2100.

Changes are taking place every day, even as we are reading this article, such as the appearance of new capture devices, improvements in video signal digitization, the rise of broadband and 5G mobile telephony, a change in trends on AV content consumption, improvements in lighting equipment, the implementation of UHD (Ultra High Definition), 4K or 8K, the expansion of IP and Cloud environments, social media, video-on-demand platforms, content generated in virtual environments or backward-compatible transcoding streams, among others.

These changes will continue to have an impact what we call the color of an image but following the current trend: better and wider color range in audiovisual content.