Calibration chart with color patches, gradients, and grid overlay — shot before lens tests, white balance, or color grading. Documents optical and color characteristics in that lighting setup.
You shoot a test recording before principal photography begins or during a setup — a structured pattern of colors, gray scales, and geometric lines that documents the camera under precisely this lighting configuration. This is your grid chart, your optical diary for this hour in this location. Unlike unplanned reference shots, the chart provides you with reproducible measurements: how the lens refracts colors, where vignetting begins, whether the sensor still holds detail information in the shadows or is already tending towards noise.
The classic composition shows color patches (often a variation of the ColorChecker or Pantone scheme), a gray wedge from pure black to white — typically in 10 or more steps — and a fine grid for controlling lens distortion and focus sharpness across the entire image field. Some charts also integrate Siemens stars for resolution tests or target marks for quick focus calibration. You shoot the chart at least at normal exposure, often also with 1–2 stops above and below the main light, to push the sensor's headroom to its limits.
The practice: Before color grading, you place this footage on the timeline, precisely set the gray values to middle gray — the LUT or grading node must keep the gray chain neutral, otherwise any subsequent color correction will be distorted. In editing, the chart becomes comparison material: scenes shot under identical lighting conditions should have similar color tones to the chart, otherwise your white balance or lighting is incorrect. For multi-camera shoots — two different cameras, one scene — the most direct way to color matching is: both cameras shoot the same chart consecutively, then you match the LUTs accordingly.
Digital charts (printed on high-quality paper, preferably matte or semi-gloss surface to minimize reflections) last longer and are transport-friendly. Some DoPs also use digital displays, but with the disadvantage that the display calibration itself is not guaranteed. The chart should always lie flat in the image field — no perspective, no rotation — and occupy approximately 1/3 of the framing. If you shoot it too small, you lose detail information in the fine lines; too large, and you cannot control the homogeneity of the light across the entire field.