How should I set white balance from a gray card when the card shows different color casts across the frame?
Asked 10/2/2012
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I photographed a gray card in a forest so I could set white balance later from the RAW files, but the card doesn’t look uniform. Sampling different spots gives very different readings, roughly 5900K to 7000K. I defocused the lens to smooth the card and tried noise reduction, but I still get inconsistent results. What’s the right way to use a gray card for white balance when the light is mixed or uneven, such as forest shade, sky light, sun patches, or colored reflections?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Gray card is used to make your colors neutral from the tone of a light source. When you have multiple light sources with different color temperatures (such as sunshine, blue sky lighting the shadow areas, and reflections colored by surrounding objects) you can only pick one of them to be the "neutral" light.
So if you have multiple light tones, it's your creative choice which light you want to consider "neutral". Often, the main light is chosen to be neutral. In daylight, this gives blueish shadows. Or you could pick a shadow area to be "neutral" and have the warmth of lit areas emphasized by warm tones. Or you could even pick something in between, such as "average" color of the gray card area, to have colors in all the lights slightly off, but overall not emphasized in any general direction.
If you want fully neutral color reproduction, you will have better luck by carrying out your shoot in a studio - where you can control the tonality of all the lights and reflections. On location, you can alleviate the problem of different color temperatures by using your own fill light (with color temperature matched to the main light) to overpower the existing fill light.
Originally by user4390. Source · Licensed CC BY-SA 4.0
user4390
13y ago
0
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This usually means the light on the card wasn’t a single, uniform color. In a forest you often have mixed illumination: direct sun, blue skylight in shade, and green or warm reflections from surroundings. A gray card can only neutralize one light source (or one chosen balance point), not all of them at once.
So the differing readings are expected. Pick the reference based on your intent:
- neutralize the main light,
- neutralize the shadows,
- or choose an average sample if you want a compromise.
For white balance, exact brightness on the card is less important than the card being neutral and not overexposed. If any sampled area is clipped, it won’t give a reliable result.
Practical approach:
- sample a clean, non-clipped area of the card,
- avoid hotspots or strongly colored reflections,
- if the card spans mixed light, use an average reading rather than chasing a single “correct” Kelvin value.
In mixed light there may be no single correct white balance—only a creative choice about which light you want to look neutral.
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