Introduction

As part of my PhD research into auditory-visual associations and how Virtual Reality (VR) can be used as a tool to understand and potentially strengthen cross-modal associations between the two senses, I have stumbled upon an area that requires deeper investigation. How colour is perceived within the VR environment can be crucial when conducting research studies, especially when comparing VR and standard displays. Colour management, colour space, colour gamut, and calibration are important aspects to consider when making your VR application as realistic and true to life as possible.

As part of my recent research, I have been designing a study that compares an auditory-visual association test performed on a standard display with a similar test in VR with an app created with Unity. Both displays perform a similar test, but the Unity app will use unique features of VR to give insights into our associations between our senses. It is important to understand, highlight, and find solutions to potential issues when comparing colours between a standard display and the VR Head Mounted Display (HMD). Different HMDs use various colour spaces and specifications. As a result, colours will be presented differently on an HMD compared to a standard display, and even among different HMDs. In this post, I will explore colour management and colour spaces in relation to standard displays, Oculus Quest 2, Unity, and briefly how other HMDs differ.

Standard Displays

First, I would like to discuss standard displays and look at how colour is managed on the majority of screens we use every day. Colour management and colour space are important concepts when it comes to producing accurate and consistent colours on standard displays, such as computer monitors and televisions. Colour management is the process of ensuring that colours are consistently represented across different devices and platforms. This is achieved by using colour profiles, which are essentially sets of data that describe the colour characteristics of a device or display. Colour profiles can be used to adjust the colours on a display to match a specific standard or to produce colours that are consistent across different devices [1].

Colour space refers to the range of colours that a device can display. The most common colour space used for standard displays is sRGB, which is a standardized colour space that is widely supported by many devices. Other colour spaces, such as Adobe RGB and DCI-P3, have a wider colour gamut, which means they can display more colours than sRGB. However, most standard displays are not able to display the entire range of colours defined by these colour spaces. Colour space specifications also define a white point, which represents what chromaticity the response to maximum drive to the primaries should be [2]. The standard white point is usually set to D65 on standard displays; however, this can be different for VR HMDs, as we will show next.

Virtual Reality Displays

The standard colour space in VR is not well-defined, as it can vary depending on the device, the display technology, and the application. However, the most common colour space used in VR is Rec.709. Rec.709 is a narrow colour gamut used in almost all internet and non-HDR content. It is the default colour gamut used in the sRGB standard and is commonly used by Liquid Crystal Display (LCD) panels [3]. For the Oculus Quest 2 HMD, the default colour space is Rec.2020, with a white point of D65. Other Meta HMDs use different colour spaces and white point combinations, like the Rift S, which uses Rec.709 with a D75 white point, or the Oculus Go, which uses Rec.709 with the D65 white point. For more information on the differences in specifications among the Meta line of HMDs, you can find them on their device specification page.

While Rec.709 is closer to the standard used in standard displays, one of the new colour spaces, ITU’s Rec.2020, will be important for VR in the future. It uses pure wavelengths generated from lasers to define the red (630 nm), green (532 nm), and blue (467 nm) primaries [2]. It has a wide colour gamut commonly used by HDR UHD TVs, covering almost all the colours the human eye can perceive, which is wider than the Rec.709 standard [3].

Another challenge with producing consistent colours in VR applications is that VR devices often have different display resolutions and pixel densities, which can also affect the way colours are reproduced. For example, a VR device with a higher display resolution and pixel density will typically be able to reproduce colours with greater accuracy and detail than a VR device with a lower display resolution and pixel density. This can be particularly problematic when VR applications are designed to be used on a range of different devices, as it can be difficult to ensure that colours are accurately reproduced across all devices.

In addition to colour spaces and display resolutions, there are differences in the types of lenses that HMDs use. The common types are Liquid Crystal Display (LCD) and Organic Light-Emitting Diode (OLED) displays. LCD panels are an older technology and are also a standard for use in non-VR displays. Due to their lower price point, they have been used in more affordable VR headsets. While OLED technology has some advantages, such as a thinner profile, lighter weight, and lower power consumption, it is a newer technology and is more expensive [4]. Since it is a new technology, more research is needed, as OLED chemistry isn’t very consistent, and the primaries and white point can drift somewhat from panel to panel [2].

Managing Colour in Unity

When you are developing your own applications, in Unity or Unreal Engine, focusing on colour and how your application will look across different devices is an important aspect. I develop VR apps using Unity, and it has a great integration package for Oculus Quest HMDs. In Unity, when using the Oculus integration package for developing VR applications, you can change the colour gamut in the settings. The colour space is set to “Linear” by default, and this means that the colours in the game are being processed using a linear colour space as opposed to a gamma-corrected colour space [5].

In a linear colour space, colour values are proportional to the physical intensity of the light they represent. This means that if the colour value is doubled, the physical intensity of the light is also doubled. This is the way that light behaves in the real world, and it is more physically accurate [6].

A gamma-corrected colour space, on the other hand, uses a non-linear relationship between the colour values and the physical intensity of the light. This is done to compensate for the non-linear way that the human eye perceives light. Gamma correction is commonly used in displays and other devices that produce light, to make the image appear more visually consistent across different lighting conditions [6].

In Unity, colour management is a feature that allows you to ensure that the colours in your game or application are displayed accurately on different devices and platforms. To set up colour management in Unity, you will need to do the following:

1. Open the “Project Settings” window by going to “Edit > Project Settings” in the top menu.
2. In the “Project Settings” window, select the “Player” option from the list on the left.
3. In the “Player” settings, scroll down to the “Color Space” section and select the colour space that you want to use for your project, either Linear or Gamma.

It’s important to note that when targeting VR platforms, it’s recommended to use the Linear colour space, as this will give you more control over the colours in your scene and allow you to achieve more accurate results.

Another way to change the colour space is with the Oculus Integration Unity package, which lets you override the colour space of the headset at runtime. If you do not see any issues with the output from the default colour space, do not use this setting. Leave it disabled to use the default color space of the headset.

1. In the “Hierarchy” view, select “OVRCameraRig”.
2. In the “Inspector” view, under “OVRManager” > “Display”, select “Enable Specific Color Gamut”.
3. From the “Color Gamut” list, select the colour space you want your headset to use at runtime. Options include: Unmanaged, Rec.2020, Rec.709, Rift_CV1, Rift S, Quest, P3 and Adobe_RGB.

For more information on colour space using the Oculus Integration Unity package, click here [5].

Comparing Colour Between Standard and VR Displays

If you are looking to have as close a colour match between a standard display and an HMD, there are a few other things to mention. While it can be tricky to exactly match the presentation of colour on the two displays, there are a few things to check before making the comparison.

When comparing with other VR devices or other displays, it is important to take into account the following:

1. Device variability: Different devices, such as headsets and monitors, can display colours differently due to differences in their display technologies and calibration. This can make it difficult to ensure that colours are displayed consistently across different devices.
2. Viewing conditions: The lighting conditions in which a VR experience is viewed can also affect how colours are perceived. For example, a room with bright ambient light may wash out the colours displayed on a VR headset, while a room with dim lighting may make it difficult to see subtle differences in colour. The conditions of the real-world environment would need to be the same in the VR space to be able to compare the colours on the two displays.
3. Colour space: Different devices and operating systems use different colour spaces, which define the range of colours that can be displayed. This can make it difficult to ensure that colours are displayed consistently across different devices and operating systems.
4. Other tips: Make sure that you calibrate both displays to ensure they are reproducing colour accurately. Use the same colour space on both displays, and you could also use a colour reference, such as a Pantone swatch book, to compare the colours on the displays.

Keep in mind that it may not be possible to perfectly match the colours on the two devices, as they may have different colour capabilities and be affected by different viewing conditions. However, by following these steps, you should be able to improve the colour match between the two devices.

Another issue when presenting colour in VR applications and across multiple displays or devices is that different users may have different perceptions of colour, due to variations in their visual acuity and other factors. This can make it difficult to ensure that the colours displayed on the devices are perceived consistently by all users. To address this issue, it is important to carefully consider the needs and preferences of the target audience when designing a VR application. This may involve using colour schemes and palettes that are specifically designed to be easy to perceive by a wide range of users, and using colour-blind-friendly designs where appropriate.

Conclusion

In conclusion, managing colour in VR applications is a complex and challenging task, especially when considering the compatibility with both VR and standard devices. The constantly evolving nature of VR technology and varying specifications of devices like Meta’s headsets can make it difficult to establish definitive standards for colour management.

As VR continues to gain traction in the consumer market, it is crucial to focus on increasing the knowledge and understanding of VR devices and their specifications. By doing so, we can work towards creating more defined standards and guidelines for colour management in VR, ultimately ensuring a consistent and high-quality visual experience for users across various devices and platforms.

Despite the current challenges, developers and researchers can still work towards optimizing colour management in their applications and studies by keeping in mind the diverse factors that influence colour perception. This includes understanding device variability, considering viewing conditions, and catering to the needs of the target audience. By staying informed and adapting to new developments, we can continue to advance the field of VR and deliver increasingly immersive and visually stunning experiences.

References

[1] – ‘Color management: Keeping Your Colors Consistent’. https://aelaschool.com/en/visualdesign/color-management-keeping-your-colors-consistent/ (accessed Jan. 25, 2023).

[2] – ‘Color Management in Meta Quest Headsets | Oculus Developers’. https://developer.oculus.com/resources/color-management-guide/ (accessed Jan. 25, 2023).

[3] – ‘Color and Brightness Mastering Guide | Oculus Developers’. https://developer.oculus.com/resources/color-brightness-mastering/ (accessed Jan. 25, 2023).

[4] – M. C, ‘OLED vs LED for Virtual Reality Headsets: Which is the Best Display?’, VR Expert | Enterprise VR/AR Hardware Supplier, Jun. 20, 2022. https://vr-expert.com/oled-vs-led-for-virtual-reality-headsets-which-is-the-best-display/ (accessed Jan. 28, 2023).

[5] – ‘Set Specific Color Space in Unity | Oculus Developers’. https://developer.oculus.com/documentation/unity/unity-color-space/ (accessed Jan. 25, 2023).

[6] – ‘Gamma and Linear Space – What They Are and How They Differ’, KinematicSoup Technologies Inc., Jun. 15, 2016. https://www.kinematicsoup.com/news/2016/6/15/gamma-and-linear-space-what-they-are-how-they-differ (accessed Jan. 28, 2023).