Giving Thought to White Balance and Color Temperature in Digital Images
Many years ago, back in the days of wired telephones and film, most photographers did not give white balance (WB) or color temperature much thought. Those who did would carry around color-correction filters to screw onto the front of their lenses that would cancel out the color casts of the artificial or natural light illuminating a scene. If you were paying attention back in those ancient times, you may have noticed that some film was marketed specifically for indoor or outdoor use or specific light sources.
My guess is that many digital photographers do not give color temperature or white balance much thought, either. In fact, I pretty much know this because, when I shop on the Web, I see many examples of images that show a definite color cast. This is not usually a big deal unless you are shopping for a ceramic bowl with a cream-colored center and the color cast of the shot makes the bowls with white centers look cream-colored. In photos, generally, we want white things to look white.
Your eyes, by the way, are incredibly good at removing color casts from the scene registered in your brain. White objects look white to our eyes unless heavy filtration is added to the light source or, in the case of a setting or rising sun, the sunlight passes through an abundance of atmosphere, causing the light to shift to a more yellow, or “golden,” cast.
So, if you are shooting a digital SLR or mirrorless camera, or even an advanced point-and-shoot, you may have stumbled across a menu setting or button that allows you to adjust the white balance in the camera. In this discussion, we will talk about how and why you might want to adjust that setting so that, from this point on, I don’t buy a bunch of cereal bowls on the Web that are the wrong color.
What in the world is white balance, you ask? Well, basically, it is a setting that tells the camera how to register color temperature. Um, what does “temperature” have to do with “color?” Well, color temperature is a measurement of the hue of a particular light source. It is measured in degrees Kelvin. We measure cold and heat with thermometers calibrated to show us degrees, so how come we are talking about color using the same unit of measure? Well, thanks to Lord William Thomson, the 1st Baron Kelvin (a British engineer and mathematical physicist who was directly responsible for forming the first and second laws of thermodynamics) who heated carbon, an “incandescent radiator,” and noticed that as it got hotter, the color of the carbon changed as it heated, we have a color-temperature scale. The hot-or-cold Kelvin temperature scale starts at absolute freezing 0K (-273.15ºC) while the hue-based Kelvin scale relating to color temperature starts with black as the zero point. The visible spectrum of the Kelvin scale ranges from about 1700K to 12000K or more. To the left of the visible portion of the scale is infrared. To the right is ultraviolet.
Have you ever noticed how the stars in the night sky are different colors? Well, this color is directly attributed to the surface temperature of the star where blue and white stars are hotter than yellow and red stars.
Still with me? Like many subjects we have discussed, you can easily dig deeper into the topic, but, for the photographer, what you need to know is that every light source emits light with a unique hue and that hue is measured in degrees Kelvin. Want to solidify the bridge between Kelvin’s temperature and hue? In his later years, the lord served on the board of Kodak Limited, a British company affiliated with Eastman Kodak. Further tying the “temperatures” together, while adding a bit of confusion, we are accustomed to saying that colors that move toward red are “warm” and colors towards blue are “cool,” even though the cooler colors have higher Kelvin temperatures.
So, let’s get back to photography. When you are out taking photos, be it outside under the sun and clouds, or inside using lamps or strobes, the light emitted from every light source casts its own hue on the scene. Fluorescent light has a different hue than tungsten, which has a different hue than candlelight, which has a different hue than quartz, which has a different hue than sodium vapor, etc. Many modern LED lights for video and photography feature adjustable hues, or they might be daylight or tungsten balanced out of the box. These hues can either be captured by your camera’s sensor or film, or it can be neutralized with filters or electronics so that the white interior of the cereal bowl, photographed beneath a “warm” incandescent light bulb, still looks white instead of beige.
As I stated earlier, in the days of film, or if you shoot film today, you can get indoor- or outdoor-balanced film, or add filters to your lens to cancel out the color cast. With digital cameras, you can select a white balance setting for your camera to remove the color cast digitally.
Most digital cameras have the following white balance settings: Auto (A), and then, from warm to cool, Tungsten (light-bulb symbol), Fluorescent (symbol resembling a light tube), Daylight (sun symbol), Shade (a house casting a shadow symbol), Cloudy (cloud symbol), Flash (lightning-bolt symbol), or Manual/Preset. The manual/preset option allows you to dial-in a specific Kelvin-degree setting. One thing you need to know is that these preset WB settings do not guarantee that you will neutralize a color cast. Kelvin temperatures for specific lights are estimates and not precisely matched to each and every light source out there. For example, the sun changes color temperature as it moves across the sky, due to the ever-changing thickness and makeup of the atmosphere that filters the light. Also, we are usually being bombarded by multiple light sources when not in a controlled studio environment. Sitting at my desk here, I have fluorescent lights above, the illumination of the computer screens before me, and cloud-filtered sunlight coming in through the office windows.
White Balance in Photos
Now that we are experts on color temperature and white balance settings, we need to figure out a plan for using this in our photography. And, before I get started down this path, let me assure you that there are a great many different opinions on how to proceed here, so, if you have heard something else, or want to share other ideas, please feel free to fill up the comments section below with your suggestions, tips, or thoughts. Also, know that there is no one correct way of using your camera’s white balance settings. I’ll return to this thought at the end, after I run the risk of stirring the proverbial pot.
There are three basic approaches you can take to white balance: 1) you may leave your camera on Auto WB and let the electronic brain inside your camera evaluate the scene and then try to figure out the best white balance to use, 2) you can observe/estimate the color cast and dial a pre-set WB based on the lighting conditions (sunny, cloudy, shade, fluorescent, etc.), or 3) you can set the WB by manually setting the Kelvin temperature to a neutral (white or gray) point in the scene or on a dedicated “gray card.” The manual method requires that you either add a gray card to the scene in a test shot or calibrate to a neutral area of the frame and then take another photo with the white balance adjusted. Many cameras have specific procedures for measuring a manual WB setting. To figure out how to manually set a custom white balance with your camera, grab your manual, or the Internet, and give it a try.
Whichever method you choose, white balance is something that can also be adjusted in post processing by many photo-editing software systems. If you are shooting RAW images, you will have a greater control of white balance adjustments in post processing. With JPEG images, you may still be able to adjust white balance after the image is captured, depending on what kind of software you are using, but the level of adjustment will be less effective than what you can achieve with the RAW images.
If you correctly select your WB manually, or use a WB preset that is spot-on, when you look at your image on your LCD, or on your color-corrected monitor at home, white objects will appear white in the photograph. Other colors will be true as well. Many times, Auto WB will work great for you, but Auto WB is often confused by multiple color temperature light sources. However, if due to a misreading by the Auto WB setting or an erroneous manual WB setting, the image has a color cast, then you can work on neutralizing that color cast in post processing by using the software’s white balance presets, or an eyedropper tool to select a neutral-colored (usually gray) area of the image so that the software sets a specific white balance to neutralize the hue.
One mistake I have made, many times, is that I will forget to change my white balance back to the original setting after I have tweaked it for a series of photos. I’ve been known to do the same with ISO and Image Quality settings. Ugh. If you always leave your camera on Auto WB, you will never have to worry about taking a full day’s worth of photos in the bright sun with your white balance set to eliminate a tungsten color cast. If you already feel overwhelmed by the multitude of options that your digital camera is presenting to you, please do not feel like you have to now throw white balance onto that pile. I am sure many “pros” will say that I am leading you down a path toward destruction, but I generally set my white balance to Auto and neutralize (or not) in post processing.
Go with the Flow
Remember what I said above about there not being one correct way to go about adjusting white balance? Well, I will stand by that. I’ve said it before, and I will say it again: photography is art. Art is subjective. Therefore, if you take an image that has a decidedly blue color cast, either because you told the camera to give it that cast, the camera was set incorrectly, or the camera’s Auto WB missed, and you like that blue color cast because you feel that it works for that image, then there is absolutely no rule of photography that says you need to neutralize your white balance for that image—or any others.
In my own night photography, I often struggle with how to deal with color casts. I generally shoot with Auto WB and then I debate, in post processing, if I should neutralize the color cast from street lamps or other light sources. There are times where I leave the cast in the image, and there are times when I attempt to neutralize it. It all just depends on how I feel about the image and the effect the color cast has on the mood and feel of the frame. Of course, there are times when accurate color rendition is needed in a photograph, be it for commercial or certain artistic demands.
The bottom line on white balance is that it is up to you, the artist, on how and when to adjust your white balance, or to adjust it at all. Hopefully, this article serves to give you a bit of background knowledge and a plan for how you deal with color casts, moving forward in your photography.
The only time you should definitely, absolutely, remove color casts in your photos is when your product shots on the Web are going to cause me to buy the wrong cereal bowls!