Video Signal Paths: Pixel Maps, Bandwidth and EDID

Draw the actual signal chain

List the content file, decoder, graphics output, switcher, extender, processor, receiving hardware and display. At every boundary, record resolution, frame rate, colour encoding, chroma sampling, bit depth and range. A device may support a high resolution and high bit depth individually while requiring a different combination when both are used together.

Distinguish the transported video frame from the physical LED pixel map. A processor can receive a standard canvas and map only part of it to the wall. Record crop coordinates, rotation, scaling and receiver allocation. Keep native-pixel diagnostic files alongside the finished content.

Estimate active-picture data

For uncompressed RGB or 4:4:4 samples, active data rate is width × height × frames/s × 3 × bits/component. A hypothetical 3840 × 2160, 60 frames/s, 10-bit signal contains 14.92992 Gbit/s of active sample data. This calculation excludes blanking and transport coding. Interface selection must use the actual link mode, overhead, cable specification and device capability.

Chroma subsampling reduces chroma sample count. At the same dimensions and component depth, 4:2:2 carries an average of two component samples per pixel and 4:2:0 carries one and a half, compared with three for 4:4:4. Those are sample-count comparisons rather than universal connector line rates. Compression adds another independent variable.

Use EDID as configuration evidence

EDID communicates display capabilities to the source. Intermediate equipment can pass, combine or emulate that information. Save the EDID presented at the source and confirm the output mode actually selected. A supported mode in an EDID record is not a test of the complete installed cable path.

For fixed installations, document who owns the EDID configuration and where its backup is stored. Confirm that the required mode returns after a cold start, input switch, display power cycle and cable reconnection. If protected content is required, test the corresponding HDCP path separately.

A practical diagnostic sequence

• Start with a known source and a short, verified connection to the processor or display.
• Verify native geometry using borders, coordinates and single-pixel patterns.
• Check fine coloured text, neutral ramps and black/white clipping.
• Add each transport or switching stage and repeat the checks.
• Test the actual installed cable route, power sequence and recovery behaviour.

Record whether a fault follows a source, input, cable or output. Internal patterns help isolate downstream behaviour but may bypass input conversion. Keep their results separate from those of the external playback chain. Release the final topology, configuration exports and reference media together.