Auto White Balance Versus the Sunset
Your eyes can compensate for the color cast of a wide variety of light sources. With auto-white balance, so can most cameras. But sometimes your camera can compensate too well.
First off, let's look at human vision for a moment. Generally, it's not something we pay much attention to. It's just there. Our eyes and vision are so inherent in how we interact with the world we tend to ignore that conduit and see (literally) only the world itself. Our vision itself (as a thing) basically disappears. It's like a window in a building. Most of the time, we look through it, not at it. We are rarely aware of our vision when it doesn't work the way we expect it to. As I've gotten older, I now where glasses. When I was younger I didn't, but gradually I became aware that it was harder to read the fine print on things than it used to be. Many of you can no doubt relate. Many of you who can't yet will one day.
But we don't need to wait for the inexorable process of aging to make its presence known before we notice how the functioning of our vision affects what we see. It does so in more subtle ways every day throughout our lives. Without us really noticing, our vision system goes about its job of stitching together a seamless wrap-around mural of our surroundings. Even though our eyes are only ever focuses in a single direction at any given time, we have the perception that what surrounds that is still there because we saw it there recently. We remember that it's there and our perception tells us it still is even when we turn our gaze elsewhere.
Perhaps the function of our visual system that goes the least noticed though is the way our eyes and brain automatically compensate for a wide range of color temperature differences caused by differences in the light source. Regardless of whether it's the warm hues of incandescent light, the cooler hues typical of LED lighting or the eerily green shades of many fluorescent sources indoors, or the gradual procession from warm to cooler and back to warm outdoors as world around us goes from sunrise to midday to sunset, everything looks pretty much normal to our eyes. We simply don't see the lighting color cast that surrounds us. Somehow, all gets compensated for, completely automatically.
I remember when I first started getting interested in photography. At first, I shot print film because slides seemed too complicated. But to get the best quality and control possible I knew I needed to transition to slides. When I first did so though, I was shocked at just how orange my indoor photos appeared. It was as if someone had placed a strong warming filter over my lens even though I knew this wasn't actually the case. When I shot those images, everything looked fine to my eyes, but to the camera, all my friends and indeed my entire house came out horribly orange colored. The entire roll was an unusable loss.
It did though serve to teach me about color temperature and white balance. What we take for granted every day as we go about our lives was actually there the whole time even though I couldn't see it myself. And it would ruin my images if I didn't take it into account and correct for it. With film, we had to correct for the color temperature of light by using film tailored to that lighting source or by using color compensating filters in front or our lenses. All this arcane nonsense is mainly a thing of the past with digital photography today. Cameras can electronically compensate for color temperature without the need for filters or other the use of different sensors.
While it is possible to manually set camera white balance, most shooters take the easy way out and set their cameras on auto white balance. This lets their cameras automatically compensate for color temperature just the same as their eyes do. This would be the end of the story for many such shooters, but not for anyone serious about their photography.
Just as our eyes can be aware of lighting color if the color cast is extreme enough, there are limits to how well our cameras can compensate as well. In particular, a camera has no real idea what it's looking at. Human vision can rely on history, experience and context to help provide cues as to that it's seeing. Your camera has none of that.
Think about it. Let's take a blank white sheet of paper as an example. When you look at it indoors, how do you know it is indeed white and not orange? You know because you're familiar with what paper is and what it looks like. Your camera has never heard of paper. The only thing your camera has to go on to correct white balance is to assume that a typical scene is, on average ... average. It simply has to assume that if it averages out all the colors in an image that things will net out to a neutral hue. A photograph of a white piece of paper indoors would be orange everywhere, not just the paper. If a camera wants to compensate for all this orange it has to assume that the right answer has to be closer to medium toned than orange. And thus it shifts all the colors accordingly and we end up with white paper in the image. A camera tries to be cleverer than just this, but it can never compete with the human brain when it comes to contextually compensating for color cast.
And all this leads me to where I wanted to be, the topic of photographing a sunset. When you look at a sunset you see the glowing warm hues it casts on the surrounding landscape and admire its beauty. When a camera set on auto white balance sees the same thing, it sees a heck of a lot of orange and does its best to neutralize it. This is somewhat the same as what happened way back when first started out shooting print film. Those automated film printer machines employed much the same method of compensating for color casts as does a digital camera today. Neither have any real idea what a given image is actually of, and both make the assumption that a typical scene shouldn't have an obvious color cast. One of the main things that finally pushed me into switching to slides was the lackluster appearance of every sunset picture I shot on print film. I just knew the sunset was more vibrant than what my prints ended up portraying.
Auto white balance works the same way. It's great for removing a color cast under average conditions. It sucks when you actually want that warm glow from sunset to show in your images. It won't likely remove all the color so long as there is some less saturated areas in the shadows and elsewhere, but it almost certainly will decrease the very thing you set out to capture. Yes, some photographers need to capture accurate color at any hour, but as predominantly a landscape photographer myself, I often shoot as early and late in the day specifically to capture the color of light that only exists at those hours. And I want to celebrate it, not diminish it in my images.
Which version looks better to you?
It's not all bad of course. While camera white balance does get permanently baked into jpeg capture it has absolutely zero impact on raw images. Lightroom, Adobe Camera Raw and other raw converters allow you to freely adjust white balance to improve your image appearance as you see fit. You can make a sunset look even more orange than it actually was. You're in control so long as you shoot raw and not just jpeg.
It is worth noting though that the jpeg version is used for the camera back LCD image. If you look at your images after shooting to double check what you ended up with, your camera white balance setting does alter what you see. I do generally leave my camera on auto white balance, but I know I'm not bound by what my camera LCD shows me in terms of image potential. But if you weren't aware of this, you may find yourself feeling like your next sunset isn't really as photogenic as you first thought it was. And that would likely be a shame since you can compensate — and then some — during raw conversion later.