5.4 Field of view, resolution, and refresh rates
3 min read•august 7, 2024
AR/VR displays are all about immersion and performance. Field of view, resolution, and refresh rates are key factors that make or break the experience. These elements determine how realistic and smooth the virtual world appears to users.
Getting these display characteristics right is crucial for creating believable virtual environments. High refresh rates and frame rates reduce , while good resolution and make images sharp and clear. It's a balancing act to optimize all these factors.
Display Characteristics
Field of View and Angular Resolution
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- Field of view (FOV) refers to the extent of the observable world that is seen at any given moment
- Measured in , with a larger FOV providing a more immersive experience
- Human binocular FOV is approximately 114 degrees vertically and 190 degrees horizontally
- AR/VR devices aim to match or exceed the human FOV for increased immersion (Oculus Rift has a 110-degree FOV)
- is the amount of detail that can be seen within the FOV
- Determined by the number of (PPD) of the display
- Higher angular resolution results in sharper and more detailed images
- Insufficient angular resolution can lead to a pixelated appearance and reduced (PlayStation VR has a PPD of around 10)
Pixel Density and Screen-Door Effect
- Pixel density refers to the number of per unit area on a display
- Measured in (PPI) or (PPC)
- Higher pixel density displays produce smoother and more detailed images
- Low pixel density can result in visible individual pixels and reduced image quality (HTC Vive has a PPI of 447)
- (SDE) is a visual artifact caused by the visible gaps between pixels on a display
- More noticeable on displays with lower pixel densities
- Can create a mesh-like appearance, similar to looking through a screen door
- SDE can be mitigated by increasing pixel density or using advanced display technologies ( displays have reduced SDE compared to )
Rendering Performance
Refresh Rate and Frame Rate
- is the number of times per second that a display updates its image
- Measured in (Hz), with higher refresh rates resulting in smoother motion and reduced motion blur
- AR/VR devices typically require high refresh rates (90Hz or higher) to minimize motion sickness and provide a comfortable user experience
- Low refresh rates can cause flickering, judder, and increased (Valve Index supports refresh rates up to 144Hz)
- refers to the number of images (frames) that are rendered and displayed per second
- Measured in (FPS), with higher frame rates resulting in smoother animation and motion
- AR/VR applications should aim to maintain a consistent frame rate that matches the display's refresh rate to avoid judder and visual artifacts
- Inconsistent or low frame rates can break immersion and cause discomfort (Oculus Rift S runs at 80FPS)
Foveated Rendering
- is a technique that reduces the rendering workload by decreasing image quality in the peripheral vision
- Exploits the fact that human visual acuity is highest in the central region of the retina (fovea) and decreases towards the periphery
- Renders the center of the image at full resolution while progressively reducing the resolution towards the edges
- Can significantly improve rendering performance and allow for higher resolutions and frame rates in the user's area of focus
- Eye-tracking technology is often used to determine the user's gaze direction and adjust the foveated rendering accordingly (FOVE 0 headset incorporates eye-tracking for foveated rendering)
Key Terms to Review (20)
Angular Resolution: Angular resolution refers to the smallest angle between two objects that can be distinctly resolved by a visual system, such as the human eye or a display device. It is a critical factor in determining how clear and detailed an image appears, affecting the perceived quality of visuals in augmented and virtual reality systems, where understanding spatial relationships and fine details is essential.
Degrees: In the context of augmented and virtual reality, degrees refer to the measurement of angles that describe the field of view (FOV) of a display or headset. This is essential for understanding how much of the virtual environment can be viewed at one time, which directly affects the user's immersion and experience. The greater the degrees of FOV, the more expansive the viewing area, impacting resolution and refresh rates as well.
Foveated Rendering: Foveated rendering is a graphics rendering technique that prioritizes rendering quality in the area of the visual field where the user is looking, known as the fovea, while reducing the quality in the peripheral areas. This approach optimizes performance and efficiency in augmented and virtual reality experiences by decreasing the workload on the graphics processing unit (GPU) while maintaining visual fidelity where it matters most.
Frame rate: Frame rate refers to the number of individual frames or images displayed per second in a video or digital experience. It's crucial for creating smooth motion and realism, particularly in immersive technologies like augmented and virtual reality, where high frame rates can enhance user experience and reduce motion sickness. The relationship between frame rate and factors such as field of view, resolution, and refresh rates plays a vital role in performance optimization and overall visual fidelity.
Frames per second: Frames per second (FPS) is a measure of how many individual frames or images are displayed on a screen each second. It is crucial for the smoothness and responsiveness of visual experiences, especially in augmented and virtual reality, where high FPS contributes to a more immersive experience and reduces the perception of motion blur.
Hertz: Hertz is a unit of frequency that measures the number of cycles per second of any periodic event, particularly in the context of electronic signals. In augmented and virtual reality, hertz relates directly to refresh rates, impacting the smoothness and clarity of visuals displayed to users. Higher hertz values indicate more frequent updates to the image on the screen, leading to better overall visual experience, especially during fast-paced movements or interactions.
Horizontal field of view: The horizontal field of view (HFOV) refers to the extent of the observable world that can be seen from a specific viewpoint, measured in degrees, horizontally. This measurement is crucial in augmented and virtual reality, as it directly impacts user immersion, visual comfort, and how much of the virtual environment can be perceived at any given moment.
LCD: LCD, or Liquid Crystal Display, is a flat-panel display technology that uses liquid crystals to modulate light and produce images. This technology is widely used in head-mounted displays (HMDs) for VR because of its ability to provide vibrant colors and sharp visuals while maintaining a lightweight profile, essential for user comfort during prolonged use. Additionally, the quality of an LCD panel directly affects the field of view, resolution, and refresh rates, which are critical for an immersive virtual reality experience.
Motion sickness: Motion sickness is a condition that occurs when there is a mismatch between the visual input, vestibular system signals, and proprioceptive feedback regarding motion. This dissonance often leads to symptoms such as dizziness, nausea, and discomfort, especially prevalent in immersive environments that use augmented or virtual reality technologies. The experience of motion sickness can be influenced by how effectively these systems integrate sensory information, how the field of view and refresh rates of displays are managed, and the psychological effects that arise from prolonged use of AR/VR systems.
Motion-to-photon latency: Motion-to-photon latency refers to the delay between a user's physical movement and the corresponding visual update displayed in a virtual or augmented reality environment. This latency is critical for providing a seamless and immersive experience, as any lag can lead to motion sickness or disorientation. It is influenced by various factors, including field of view, resolution, and refresh rates, as well as the methods employed for latency reduction.
OLED: OLED, or Organic Light Emitting Diode, is a display technology that utilizes organic compounds to emit light when an electric current is applied. This technology allows for thinner displays, enhanced color accuracy, and better contrast ratios compared to traditional LCD displays. OLEDs are particularly important in virtual reality head-mounted displays as they provide vibrant colors and faster refresh rates, enhancing the immersive experience.
Pixel Density: Pixel density refers to the concentration of pixels in a given area of a display, typically measured in pixels per inch (PPI). Higher pixel density results in sharper and more detailed images, directly impacting visual clarity and quality, especially in augmented and virtual reality environments where immersion is key. Understanding pixel density is essential for evaluating field of view, resolution, and refresh rates, as these aspects can influence the overall user experience in immersive technologies.
Pixels: Pixels, short for 'picture elements', are the smallest units of a digital image or display that can be controlled to represent visual information. In augmented and virtual reality, the clarity of images is heavily reliant on the number and arrangement of pixels, which directly influences resolution, field of view, and refresh rates.
Pixels per centimeter: Pixels per centimeter (PPCM) is a measurement that defines the density of pixels in a digital image or display, indicating how many pixels are present in one centimeter of the image. This term connects closely to visual clarity, as higher PPCM values typically result in sharper images, affecting both field of view and overall resolution. In augmented and virtual reality, understanding PPCM is crucial for optimizing user experience by ensuring images are rendered clearly and without distortion.
Pixels per degree: Pixels per degree (PPD) is a measure used to determine the resolution of a display in relation to the viewer's field of view. It indicates how many pixels are contained within one degree of visual angle, influencing the perceived clarity and detail of images presented in augmented and virtual reality experiences. A higher PPD value means that finer details can be discerned, which is crucial for immersion and realism in visual environments.
Pixels per inch: Pixels per inch (PPI) is a measurement of pixel density that indicates the number of individual pixels present in a one-inch span of a digital display. A higher PPI value means more pixels are packed into each inch, resulting in sharper images and finer detail. This metric is crucial for understanding the clarity and quality of visuals in augmented and virtual reality environments, where users need to perceive high-resolution graphics for a more immersive experience.
Refresh Rate: Refresh rate refers to the number of times a display updates its image per second, measured in hertz (Hz). This characteristic is crucial for AR and VR systems, as higher refresh rates contribute to smoother visuals and reduce motion blur, ultimately enhancing the user experience. Additionally, a high refresh rate helps in minimizing latency, which is vital for creating immersive environments where real-time interactions occur seamlessly.
Screen-door effect: The screen-door effect refers to a visual artifact in augmented and virtual reality where the gaps between pixels on a display become visible, resembling a screen door. This effect is particularly noticeable in head-mounted displays (HMDs) with lower resolution, causing distractions and reducing immersion by breaking the illusion of a seamless digital environment. As the field of view, resolution, and refresh rates improve, the screen-door effect becomes less pronounced, allowing for a more engaging user experience.
Vertical Field of View: Vertical field of view (VFOV) refers to the extent of the observable world that can be seen vertically within a visual display, such as a headset used in augmented and virtual reality. This measurement is crucial because it directly impacts immersion and user experience by determining how much of the virtual environment is visible to the user. A larger VFOV can enhance the sense of presence in VR, allowing users to perceive a wider vertical perspective, which is particularly important in environments that simulate real-world scenarios.
Visual Fidelity: Visual fidelity refers to the accuracy and realism of the visual representation in augmented and virtual environments. This concept is crucial as it encompasses factors such as image quality, clarity, and detail that contribute to the overall immersive experience. High visual fidelity enhances user engagement and can significantly affect how realistic an environment feels, making it vital to optimize various technical aspects that impact visual output.