Screen Gain
Gain is a numerical value that represents the inherent reflective properties of screen material (i.e., its brightness from various angles). When a specific amount of light is projected onto a perfectly diffuse reflective surface (where reflectivity is uniform across all 180-degree angles), the reflected brightness is set as a baseline value of 1. Under the same conditions, when light is projected perpendicularly onto the screen, the brightness at the center and other points along the same arc is measured. The ratio of this brightness to that of the completely diffuse surface is referred to as the screen gain.

Half-gain is a critical metric for evaluating screen brightness. It refers to the gain value when the viewer moves away from the central axis of the screen to an angle where the perceived brightness drops to half of the maximum brightness observed from the center. The viewing angle at which this half-gain occurs is known as the half-gain angle, another essential technical parameter. A larger half-gain angle allows more viewers to see a clear image from wider positions.

Impact of Screen Gain on Image Quality
Screens with no gain produce images that are neutral and realistic but are more susceptible to ambient and external light interference. In contrast, screens with gain deliver brighter, more vibrant images with richer contrast and color saturation, while being less affected by external lighting conditions. However, higher gain usually correlates with a narrower optimal viewing angle. Excessively high gain (with an overly small half-gain angle) may lead to a noticeable hotspot effect—where the center of the image appears brighter than the corners—and a loss of detail in highlighted areas due to over-saturation. Since the reflected light becomes highly directional, only one or two viewers seated directly in front of the screen may experience optimal brightness. Therefore, screen selection should be based on specific usage scenarios; higher gain is not always better.

Aspect Ratio
The aspect ratio of a projection screen significantly influences image quality. The best results are achieved when the screen’s aspect ratio matches the native resolution of the projector and the input signal source. Common aspect ratios include:

4:3 / 1.33:1 – Typically used for standard video/PC content. Width can be calculated as diagonal × 0.8.

16:9 / 1.78:1 – Ideal for high-definition television (HDTV) content.

1.85:1 – Often used for widescreen video signals.

2.35:1 – Primarily employed for panoramic widescreen formats with stereoscopic sound.

For home applications, 4:3 and 16:9 are the most commonly used formats. Users should select a screen ratio that corresponds to their projector’s display capabilities.

Resolution, Contrast, and Uniformity
Screen Resolution:
Depending on the projector technology (e.g., CRT, LCD, DLP, D-ILA, or LCOS), resolution is measured either in terms of bandwidth (for CRT projectors) or pixels (for digital projectors). Pixel-based resolution refers to the total number of horizontal and vertical pixels, indicating the true resolution of digital projectors.

Fresnel optical rear-projection screens (where the projector is placed behind the screen) may have physical structures such as lens grooves or lenticular patterns that can affect effective resolution. In contrast, diffuse rear-projection screens, rigid or flexible mats, and front-projection screens typically offer high resolution without such limitations, making them suitable for high-definition content.

Screen Contrast:
Contrast ratio is crucial for image clarity and depth, defined as the ratio between the brightest and darkest parts of an image. Higher contrast screens enhance grayscale reproduction and color gradation, contributing to a more lifelike image.

Screen Uniformity:
Uniformity affects both image quality and compatibility with projector technology. A high-quality screen ensures consistent brightness and color accuracy across the entire surface, regardless of the viewer’s horizontal or vertical angle (0–180 degrees). This characteristic also helps compensate for potential unevenness in the projector’s output.

General Selection Criteria
When choosing a screen, it is important to consider all the above parameters in the context of your specific needs. The following points are particularly critical:

The screen surface must be perfectly flat.
Any warping or “waviness” can cause image distortion and variations in projection distance, resulting in blurriness and focusing issues.

Reflectivity characteristics must be precise.
While most screens appear white, different materials reflect light—and colors—differently. Two common types of front-projection screens illustrate this:

Diffuse Reflection Screens:
These scatter incident light evenly in all directions, providing a consistent image from virtually any viewing angle. They produce soft images with wide viewing angles but are prone to interference from ambient light. In dedicated dark rooms, they perform optimally. Note that using a plain wall as a screen is not recommended due to lack of color calibration, light absorption treatment, and potential issues like color inaccuracy, dispersion, and reduced contrast.

Directional (Regression-Type) Screens:
Examples include glass-beaded screens, which reflect light back toward the source direction. This provides bright, vivid images for viewers positioned near the projection axis but reduces brightness at off-axis angles. These screens perform better in environments with ambient light since they reflect external light away from most viewing angles, maintaining image contrast.

Selection recommendations for these screen types:

For larger audiences or high-brightness projectors, choose wide-viewing-angle, low-gain screens.

Moderate gain helps improve contrast, grayscale, and color saturation.

In controlled lighting environments (e.g., dedicated theaters), both diffuse and regression-type screens work well. For living rooms, regression-type screens are preferable.

Table-mounted projectors can work with any screen type, but ceiling-mounted projectors should be paired with diffuse screens or those with a wide half-gain angle.

Viewing Distance
Screen sizes are typically indicated in inches (e.g., 80”, 120”). The optimal screen size depends on the projector’s throw distance, room dimensions, and ceiling height. The ideal viewing distance is generally three to five times the height of the displayed image. First-time users may prefer a longer distance (five times the image height), but a closer position (three times the image height) often offers a more immersive experience over time.

Mounting Conditions
The projection setup affects screen choice:

Diffuse screens (e.g., matte white) perform consistently regardless of projector placement.

Directional screens (e.g., glass-beaded) require careful alignment since they reflect light back along the incident path. If the projector is ceiling-mounted, viewers seated at standard height may perceive a dimmer image compared to those standing.

Mounting Height
The ideal installation height positions the center of the screen slightly above the viewer’s eye level. Some manufacturers minimize the top black border of screens to reduce costs, resulting in screens that are mounted too high in rooms with high ceilings. This forces viewers to look upward at an uncomfortable angle, causing strain and reducing overall viewing comfort.