Factory Calibration and Field Calibration: Why Identical Cabinets Can Still Show Colour Differences

Factory calibration reduces brightness and colour variation between LEDs, modules and cabinets under defined measurement conditions. It does not remove the need to check the finished wall after installation. The same batch can look different after transport, cabinet orientation, temperature, configuration, input content, structure reflection and viewing angle change. When a customer says that “the same model is different,” do not conclude immediately that factory calibration failed. First identify the source of the difference.

Factory calibration is tied to a production batch, a measurement condition and a configuration. If a module, receiving card, HUB, driver parameter or configuration file changes, the original calibration may no longer behave as expected. A replacement module may belong to a different batch, or a spare cabinet may not have been included in the same calibration process. The handover record should connect cabinet number, module batch and calibration file whenever the information is available.

Before field calibration, confirm the physical and electrical state. Cabinets should be aligned, locks should be engaged, mechanical pressure should be consistent, module surfaces should be clean, signal and power should be stable, receiver parameters should match and the brightness/colour mode should be fixed. If the seam, cabinet tilt or power drop is wrong, software calibration may only hide the problem temporarily. The difference may return after the cabinet is removed and installed again.

Use mid-gray, white, RGB, gradient and motion patterns. Check the whole wall, cabinet boundaries, rows and columns. If the colour difference moves with a cabinet, the cabinet/module/calibration is more likely. If it remains at a physical position, power, signal, structure or reflection is more likely. If only the camera sees it, include shutter, exposure, refresh and moiré in the analysis. Save the original state before calibration and keep the new file with a version note.

Customer acceptance should define viewing distance, angle, brightness, content and ambient light. Close-range full-white inspection is not the same as long-distance video viewing. Camera projects require the actual camera position, shutter and lens. One automatically exposed phone image cannot prove or disprove uniformity.

Create a calibration-traceability sheet with project, screen zone, cabinet number, module batch, receiver configuration, factory file, field file, operator, date and rollback file. When a cabinet is replaced later, the engineer can decide whether recalibration is needed instead of sending an unknown parameter file.

Uniformity should be reviewed before calibration and after calibration with the same content and camera position. If the physical seam is caused by a cabinet that is tilted or under pressure, calibration cannot make the mechanical line disappear reliably. If the difference is caused by a power drop, the result may change with brightness or runtime. If the difference follows a module batch, keep that evidence for purchasing and spare-part decisions.

The calibration file is also part of the system’s long-term security. Keep a read-only master copy, a working copy and an approved rollback copy. Restrict uncontrolled editing and record who sent the file to hardware. When a reseller or end customer asks for “the latest file,” identify the project and screen zone before sending it. A file with a similar name from another job is not an acceptable substitute.

When calibration is performed for a camera project, use the real camera and the customer’s target content after the visual calibration step. A result that is uniform to the eye may still show a camera difference due to shutter or colour processing. Conversely, a camera artefact should not lead to an aggressive LED calibration change without confirming the direct-view result.

Calibration should be treated as a controlled production step, not an emergency button. Schedule it after the cabinet structure, power and receiver configuration are stable. If the customer is under time pressure, record the temporary visual result and the remaining limitations instead of hiding them in a new file. The next engineer should know whether the display was fully calibrated, partially adjusted or only tested with a temporary scene.

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