Why can bright red objects look orange in direct sunlight on a phone camera?

Asked 3/27/2015

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I noticed that on my LG Nexus 5, bright non-metallic red surfaces in strong sunlight can photograph as orange. In this example, most of the scene is shaded but part of the red car is lit much more strongly, and the light may also include mixed color temperatures. The same effect does not happen on my Nikon D800 or Hasselblad H4D. What is the technical reason for this, and is it mainly caused by exposure, white balance, or sensor limitations?

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

Photography Stack Exchange contributor

11y ago

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How can this be explained technically?

Auto Exposure and Auto White Balance.

The camera is trying to expose the image properly, but there's a huge difference in brightness between the shaded areas (most of the scene) and the foreground that's lit by strong direct sun. In order to get most of the image exposed correctly, it has to overexpose the car door and fender.

In addition to two different light intensities, the camera also has to deal with two different color temperatures. Most of the scene is in shade, where the ambient light has a strong blue component, while the bright sunlit areas have much more red and yellow. In order to adjust the white balance to suit most of the photo (so that the Thrifty truck appears white instead of blue, for example), the camera reduces the blue across the entire image. This warms up the already-warmer-than-the-rest-of-the-image car door, and if the reds and yellows in that area weren't already blown out they will be after the white balance is adjusted.

Essentially, what you're seeing here is the same effect that photographers use in reverse to get deep blue backgrounds. The technique works like this: working outdoors, put a warming filter (like a "color temperature orange" gel) over a speedlite that's used to illuminate your subject. Set the camera's white balance to the tungsten (3200K) setting, so that the camera assumes incandescent light. That shifts the whole image toward blue, giving your subject normal looking skin, but making the sky much more blue. In the case with the cars, it's working the other way: you've got very yellow/red light in the foreground, but the white balance is set to compensate for blue, so you get even more yellow/orange/red in the foreground and normal-looking background.

Originally by user4262. Source · Licensed CC BY-SA 4.0

user4262

11y ago

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AI Answer

Generated from our catalog & community — verify before relying on it.

The most likely cause is clipped red channel data, made worse by automatic exposure and white balance.

In a scene with deep shade and bright sunlit areas, the phone exposes for most of the frame. The sunlit red paint can then overexpose before the rest of the image does. When that happens, the red channel hits its maximum value (“blows out”), while green may still increase. Once red is clipped, the original red-to-green ratio is lost, so the color shifts toward orange or pink instead of staying a deep red.

Auto white balance can add to this. If most of the scene is in cooler shade, the camera may adjust color for the shaded areas, which can further alter the sunlit red tones.

So yes: it is related to the camera system, but not just the sensor alone. It’s mainly a combination of limited dynamic range, JPEG processing, auto exposure, and auto white balance, which phones handle more aggressively than larger cameras like your D800 or H4D.

UniqueBot

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11y ago

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