LED Wall Mapping: Native Pixels vs. 4K Canvas
A corporate lobby will receive a direct-view LED wall 6.0 m wide by 2.7 m high with 2.5 mm pixel pitch. The wall is fed by a video processor that currently advertises a 3840 × 2160 output canvas. Sources are a 1920 × 1080 media player, a 3840 × 2160 CAD workstation, and a 1080p video conferencing codec. The client wants the CAD drawings to fill the wall "edge to edge" and the video calls to look normal. During commissioning, the CAD text looks soft and the video call is stretched horizontally; the processor is set to scale every source to the full 3840 × 2160 canvas. The wall's receiving cards are configured for their native pixel count. The client also wants a 16:9 presentation area that does not distort. You must resolve the mapping and explain the trade-offs.
1. Calculate the wall's native pixel dimensions and aspect ratio, and explain why the current 3840 × 2160 canvas is problematic.
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Native width = 6.0 m ÷ 0.0025 m/pixel = 2400 pixels. Native height = 2.7 m ÷ 0.0025 m/pixel = 1080 pixels. Native aspect = 2400:1080 = 20:9, or about 2.22:1.
The processor canvas of 3840 × 2160 is 16:9. Sending that canvas to a 2400 × 1080 wall forces a non-integer horizontal and vertical scaling and, more importantly, an aspect mismatch. If the processor scales the full 16:9 canvas to fill the 20:9 wall, geometry is distorted because 16:9 content is being stretched horizontally. If it preserves aspect, the image cannot fill the wall edge to edge without cropping. The soft CAD text is consistent with scaling a 3840-wide raster down to 2400 and then possibly scaling again inside the wall. The stretched video call confirms that the processor is not preserving source aspect. The receiving cards are not the main fault; they are being fed a canvas that does not match their native grid.
2. Recommend the processor canvas and source mapping for CAD, video conferencing, and a 16:9 presentation area.
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Set the processor output canvas to the wall's native 2400 × 1080. That removes one unnecessary scaling stage and gives each wall pixel a 1:1 mapping. Then define source windows deliberately:
- CAD at 3840 × 2160: scale to 1920 × 1080 and pillarbox within the 2400-wide canvas, leaving 240 pixels on each side. This preserves 16:9 geometry and text legibility. True edge-to-edge fill would require either cropping the CAD image top and bottom or accepting horizontal stretch; neither is acceptable for drawings.
- Video conferencing at 1920 × 1080: map to a 1920 × 1080 window, pillarboxed. Do not stretch it to 2400 × 1080.
- 16:9 presentation area: use the same 1920 × 1080 window, centered, with a neutral background in the side margins.
If the client insists on edge-to-edge CAD, explain that it means cropping content or distorting geometry, and get a written decision. For a multi-source layout, a 2400 × 1080 canvas is still correct; place 16:9 windows at native height and use the extra width for sidebars, not stretched video.
3. How would you verify legibility and geometry after reconfiguration?
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Use a test pattern with circles, a grid, and small text at several sizes. Confirm circles remain circular and squares remain square; if they do not, aspect handling is still wrong. Display a 1920 × 1080 test image and confirm it occupies exactly 1920 × 1080 wall pixels, centered, with equal side margins. Feed the CAD workstation at 3840 × 2160 and inspect fine linework and small labels from the farthest intended viewing position; if text is still soft, check that the processor is not doing a second scale after the wall input.
Verify the video call with a live far-end feed and a human face; stretched faces are immediately visible. Check that switching between sources does not change the canvas or cause a re-scale. Measure the actual displayed image height and width against the 2.7 m × 6.0 m wall to confirm no overscan. Finally, document the canvas, window presets, and source resolutions, and leave the client with a simple layout selector: CAD, video call, and presentation.