What is: Screen Door Effect, Mura, Aliasing in VR

When it comes to VR headsets, visual fidelity is a key factor that can make or break the immersive experience. However, there are several elements that contribute to visual fidelity, including the Screen Door Effect, Mura, and Aliasing. Unfortunately, these terms are often used interchangeably, leading to confusion among consumers. In this article, we will provide a clear and concise guide to each of these elements and what they actually look like.

  • The Screen Door Effect, Mura, and Aliasing are three key elements that contribute to visual fidelity in VR headsets.
  • Each element has a distinct appearance and can impact the overall immersive experience.
  • Each of these can results in an annoying artifact when gaming in VR.

Screen Door Effect

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Screen Door Effect example

The Screen Door Effect (SDE) is a common visual artifact that can be observed in first-generation virtual reality headsets such as the Oculus Rift and Vive Pro. It occurs due to the low fill factor of the display, which creates the impression of viewing an image through a fine grid of a screen door.

Pixels are small, individually lit elements arranged in an array to create a display. However, pixels are sometimes difficult to pack tightly together, resulting in gaps between them that are unlit. The display’s fill factor describes how much of the display’s area actually lights up compared to how much is unlit. The unlit spaces between pixels, which are easy to see on displays with low fill factor, cause the appearance of the Screen Door Effect.

The SDE can significantly impact visual fidelity and clarity, particularly when it comes to pixel density or PPI. To mitigate the SDE, manufacturers have started to use high-resolution displays with a higher fill factor, such as OLED and LCD panels. Additionally, lenses and meshes are being used to magnify the image and reduce the visibility of the grid.

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Personally I experienced a lot of Screen Door Effect on Oculus Quest 1, but Oculus Quest 2 and 3 are pretty much free of it.

Mura Effect

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Mura effect grainy effect example

Mura effect refers to the inconsistency of color and brightness between adjacent pixels on a display, even when the computer output to the display is a frame consisting of one singular color value. Mura effect usually happens in OLED displays, besides VR it can be experienced in Steam Deck OLED. This effect is caused by imperfections in design and manufacturing, making it difficult to achieve perfect color consistency for each pixel.

The degree of Mura effect varies depending on the display technology used. LCD displays tend to have better color consistency between pixels, while OLED displays struggle with Mura and require careful calibration to achieve decent performance. In VR headsets, OLED displays are favored for other reasons, but minimizing Mura remains a challenge.

To address Mura effect, display manufacturers use various techniques such as calibration, pixel compensation, and uniformity correction. These techniques help to minimize the visual impact of Mura effect, resulting in a more seamless and immersive visual experience for the user.

Aliasing (shimmering)

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Aliasing shimmering in VR example

Aliasing also known as shimmering in VR is a phenomenon that occurs when displaying diagonal or curved lines on a display made up of square pixels arranged in a grid. The underlying shape of the pixels and the pixel grid becomes visible, resulting in a jagged or stair-stepped appearance. This is because the square blocks can only be placed along a grid, making it difficult to draw anything but straight lines.

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Increasing the pixel density of a display can reduce aliasing because the resolution of the display allows the pixels to more precisely fit the curved or diagonal line being rendered. Anti-aliasing is another technique used to reduce perceived aliasing. It works by using different colored pixels along the edges of the line to create the appearance of a smoother line.

While aliasing is not the only factor that contributes to the overall sense of clarity when looking through a VR headset, it is one of the most noticeable. Therefore, it is high on the priority list for next-generation headsets to address. By reducing aliasing, VR headsets can provide a more immersive and realistic experience for users.

In summary, aliasing is a common issue that occurs when displaying diagonal or curved lines on a display made up of square pixels arranged in a grid. Increasing pixel density and using anti-aliasing techniques can help reduce perceived aliasing and provide a more immersive experience for VR users. Also buying the newest VR headset will help as developers are constantly working on fixing these issues and the newer VR goggles usually have these problems very much reduced. Just check out Oculus 3.

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