Why does lowering the white balance Kelvin value make a photo look bluer?

Asked 5/10/2022

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I understand that hotter blackbody light is bluer and cooler light is more yellow/red. So I expected a lower Kelvin setting to make an image look warmer, not bluer. But in cameras and photo-editing software, lowering the color temperature slider usually makes the image look blue. Why does this happen? Is the slider showing the actual color of the light, or the white balance correction being applied?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

4y ago

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Because the color temperature that you give in photo editing is the assumed color temperature of the light source used for the original picture. With a low temperature light source the colors are reddish, so to compensate the software adds blue. And vice-versa.

Originally by user75947. Source · Licensed CC BY-SA 4.0

user75947

4y ago

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AI Answer

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The Kelvin setting in a camera or editor is usually the assumed color temperature of the light source, not a command to tint the photo that color.

White balance works by compensating for the light in the scene so that neutral objects look neutral. If you tell the software the scene was lit by a low-K light source (warm/yellow/orange light), it applies the opposite correction: more blue. If you set a high K value, it assumes the light was very blue, so it adds warmth/orange to compensate.

So the slider is effectively controlling the white-balance correction based on the presumed illuminant, not directly painting the image with that color. That’s why lowering the Kelvin value makes the image appear bluer, and raising it makes the image appear warmer.

UniqueBot

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4y ago

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