Video Mapping and LED Walls for DJs: Resolutions, Scalers, Raster and Stage Processors.

LED Screens and Audiovisual Stage Design at Festivals

Large electronic music stages have replaced passive structures with architectural environments based on large-format LED screens and 3D mapping projections.

Understanding the physics of LED modules, signal transmission through dedicated processors and the design of the visual canvas (raster canvas) is essential for any video technician, VJ or production designer.

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Physical Anatomy of an LED Screen

A giant LED screen is not a single monitor, but a modular matrix built from interconnected units:

1. SMD (Surface-Mounted Device) Diodes: Tiny packages containing three diodes (Red, Green, Blue) beneath a single lens.
2. Modules or Tiles: Printed circuit boards (PCBs) grouping a fixed matrix of LEDs (e.g. 250x250 mm).
3. Cabinets / Panels: Rigid cast-aluminium structures (usually 500x500 mm or 500x1000 mm) housing modules, switching power supplies and the receiving card.

Key LED Panel Specifications

• Pixel Pitch ($P$): The physical distance in millimetres from the centre of one pixel (SMD diode) to the centre of the adjacent pixel.
  • P2.5 (2.5 mm): Ultra-high resolution for indoor stages, TV studios or close viewing ($< 3\text{ metres}$).
  • P3.9 (3.9 mm): The industry standard for outdoor and indoor festival stages.
  • P4.8 / P5 (4.8 - 5.0 mm): Giant outdoor screens viewed from far away ($> 8\text{ metres}$).

$$\text{Minimum Viewing Distance (m)} \approx \text{Pixel Pitch (mm)} \times 1.0$$

• Brightness (Nits / $\text{cd/m}^2$): Indoor screens operate between 800 and 1500 Nits, while outdoor screens require more than 4500 to 6000 Nits to compete with direct sunlight.
• Refresh Rate: Measured in Hertz (Hz). Professional panels operate at 3840 Hz or 7680 Hz, eliminating any flicker or scanning artefacts in video recordings.

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Signal Transmission: Processors and Sending Cards

Video signals travel from the media server to the LED screen through LED video processors and UTP Cat6 data cabling networks (or optical fibre), rather than conventional HDMI cables to each panel.

[ Media Server       (Resolume) ] 
              │
         (HDMI / DP / SDI)
              ▼
[ LED Processor  (Novastar / Brompton) ]
              │
        (Ethernet RJ45 / Gigabit)
              ▼
[ Daisy Chain of LED Cabinets  (Receiving Cards) ]

Main LED Processing Manufacturers

• NovaStar (MCTRL, VX Series, Taurus): The predominant global standard for flexibility, scalability and cost. It uses NovaLCT software to configure the Ethernet port map. Each Gigabit network port can carry approximately 650,000 pixels at 60 Hz 8-bit.
• Brompton Technology (Tessera SX40 / S8): Ultra-high-end processors preferred in leading global productions. They stand out for colour accuracy, HDR (High Dynamic Range) colour management, individual diode calibration (Ultra-Fine Pixel Calibration) and extremely low latency.
• Colorlight: A widely used alternative in permanent installations and mid-scale festivals.

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Calculating the Visual Raster and Pixel-to-Pixel Mapping

The raster is the two-dimensional arrangement of all pixels making up the stage’s visual map within the graphics card’s output canvas ($1920\times 1080$ or $3840\times 2160$).

A Practical Native Resolution Calculation

Suppose a stage has an LED canvas consisting of:

• 1 Central Screen measuring $6\text{ m} \times 3.5\text{ m}$ with P3.9 panels ($500\times 500\text{ mm}$ cabinets).
  • Width in cabinets = $6 / 0.5 = 12\text{ cabinets}$.
  • Height in cabinets = $3.5 / 0.5 = 7\text{ cabinets}$.
  • Pixels per P3.9 cabinet ($500\text{ mm} / 3.91\text{ mm}$) = $128\times 128\text{ pixels}$.
  • Total Central Screen Resolution = $(12 \times 128) \times (7 \times 128) = 1536 \times 896\text{ pixels}$.

To send this signal without losing sharpness:

1. In Resolume Arena, create a Slice in Advanced Output measuring exactly $1536 \times 896$ pixels.
2. Configure the NovaStar processor for pixel-to-pixel mapping, positioning the capture at the same coordinates as the HDMI/DisplayPort output.
3. Avoid any digital scaling that distorts image edges.

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Fundamentals of 3D Video Mapping on Stage Sets and DJ Booths

Video Mapping means projecting images or animated graphics onto architectural structures or real three-dimensional elements (such as the DJ booth itself, stage scenery or building façades), adapting projection geometry to the surface’s physical shape.

Key Technical Elements in Mapping

1. High-Brightness Projectors: Laser or 3-Chip DLP equipment rated between 10,000 and 30,000 ANSI lumens to ensure contrast on dark surfaces.
2. Geometric Correction (Warping): Adjusting Bezier meshes in software to compensate for oblique distortion caused by projector position relative to the surface.
3. Edge Blending: When two or more overlapping projectors cover a large surface, the software applies a progressive luminance gradient in the overlap area so the join is imperceptible.
4. Focus and Lens Offset Adjustment: Choosing short throw or long throw lenses with optical lens shift to avoid the DJ’s own shadow on the scenery.