Auto White Balance

Neutralise colour casts without per-image manual correction. Three algorithms, one CLI.

• gray-world (default) — assume the average of the scene is neutral grey. Scale each RGB channel so its mean equals the global mean. Robust on most natural scenes.
• white-patch — assume the brightest pixels are white. Per-channel -auto-level stretches each channel to full range. Strong correction; fails on scenes lacking a true white reference.
• combined — gray-world first, then a gentle white-patch pass at 50% strength. Good default for mixed-light indoor shots.

When to use

• Indoor photos under tungsten/fluorescent/LED with the wrong WB preset.
• Scanned prints / slides with age-related cast.
• Underwater or aquarium shots (heavy blue/green cast).
• Batch normalisation before publishing a gallery shot across multiple lighting conditions.

Do not use this skill when:

• Source is a RAW file (CR2/NEF/ARW/DNG/RAF) — use darktable-cli with --apply-custom-presets and the temperature module set to as shot to reference. White-balancing a baked JPEG throws away headroom that's still in the RAW.
• The cast is intentional (golden hour, sodium streetlamps for mood, blue-hour landscapes). Auto-WB will flatten it.
• The image is a deliberately monochromatic / toned edit.