CHAPTER 4 — Tint Correction and White Balance

Figure20Abnormal tints destroy the colors of your photos and results from a camera limitation associated with white balancing.

With all the high tech science in today’s digital cameras, how is it you still sometimes get these abnormal tints? How come the colors in your photos aren’t true to what you see when taking the image?

Light is fundamental to photography, and, of course, the character and quality of your photo is proportional to the character and quality of the light being captured. In today’s digital world, the character and quality of the source light captured is automatically determined by your camera.

The challenge is your camera can be exposed to multiple light sources simultaneously. In this situation how does your camera choose, which is the primary source light it should use to compute its white balance? If it chooses incorrectly your photo most certainly will not match the photo opportunity you set out to capture.

There’s a solution.

How does your camera generate an Abnormal Tint in your photos?

Digital cameras have an advantage over film because they can compute a digital white balance. What this means is they determine the primary source light for your photos and use the white color in your photo to compute a color balance to match the light source they’ve chosen. However, when your camera incorrectly identifies the light source for your photo, color distortion is guaranteed. If the incorrectly identified light source results in a significant color shift, the severe color shift is called an abnormal tint.

Lighting and the theory of Black Body Radiation

After the camera has determined the primary source of lighting, what science does it use to compute its white balance? White balancing is based upon applying the principles of Black Body Radiation theory. Black Body Radiation theory postulates that color frequencies can be exactly matched to a specific temperature. This can be a camera limitation that results in distorted color so we cover the subject fully here: 15 Ways Your Camera Distorts Color: Camera Automatic Function of White Balancing. In short, the accuracy of the color in your photos is dependent upon your camera assigning an accurate temperature representative of the qualities of the type of light in your photo. The accuracy of the temperature is important because all colors in your photo will be rebalanced by your camera using what it selects as the reference temperature for the source light. A camera is challenged with a significant number of variables when a picture is being taken but none greater than distinguishing the source of the light present.

How your camera determines the Source Light of your photos

To determine what type of light source is present in your photo the software of your camera searches your image for some representative white (or gray) color.

When such a color is identified:
• the temperature of the light for that white is estimated
• the identified white is assumed to be pure white and its temperature is then recast at 6500 degrees Kelvin, presumably because white is considered pure white at this temperature
• differential calculations for shifting the representative white (estimated color temperature) to pure white at 6500K are then applied to “rebalance” all colors in your entire photo.
The rebalancing of all colors from a known white is consistent with Black Body Radiation theory, because all colors will be on the same temperature curve – see 15 Ways Your Camera Distorts Color: Camera’s Automatic Function of White Balancing.

There are however at least four challenges with this approach:
1. Often the camera’s algorithm selects a non-representative white and then re-balances all the colors in the photo based upon the temperature of this non-representative white
2. Sometimes there’s no white in the photo and the algorithm selects a non-white color to determine the temperature from which to re-balance the photo
3. The camera selects the brightest color value as white
4. Even if the algorithm selects an appropriate white from which to balance some portion of the photo, the re-balancing is being done throughout the entire photo, and
…these challenges, as stated here, really oversimplify the reality the camera is facing.

There can be a multitude of sources of lighting for a photo

The quality and sources of light present in your photos can vary widely: ranging across a broad spectrum from direct sunlight, skylight, and cloudy situations, to moonlight and artificial lighting conditions such as fluorescent and tungsten lighting and more. Most importantly, there’s often several different light sources present when a photo is being taken. A night photo could have, for example, a combination of moonlight, sodium vapor street lamps and an automatic flash. Which temperature does your camera choose as the representative light source?

Or imagine a sunset in the mountains where a mountain casts a long shadow across a huge expanse of trees. In this case:
• you’ve got reddish light from the sun which is represented by one temperature, being a cool Kelvin temperature, (although we think of the color as warm)
• you’ve got a greenish light from the trees which could be represented by a mid level Kelvin temperature, and
• you’ve got a third temperature of light from the shadows, being a hot Kelvin temperature representing the blue end of the spectrum, (a psychologically cool color).
Which temperature does your camera choose as the representative light source?

In the previous two examples there’s really no one correct answer because there can be no single temperature representative of the multiple sources of light present in these photos. So even if Black Body Radiation Theory were a perfect solution for White Balancing, no camera could ever pick a single perfect temperature curve to represent multiple sources of light in your photos.

… and then there’s the fact that not all sources of light constitute Black Body Radiation

chartArtificial “man made” lights [such as fluorescent and various lighting sources in street lamps such as sodium vapor] discharge light in narrow spectral bands. These light sources tend to be incomplete spectrums that have color “spikes” so the color captured by your camera’s digital sensors won’t be predictable or controllable.

These types of light sources aren’t Black Body Radiation at all.
Because these challenges are known your camera often gives you a number of options to choose from.

Cameras generally give you different approaches to light source

Today’s cameras give you, usually, three broad ways to manage the white balance challenge; ie determination of the temperature of the representative lighting of your photo:

1. Automatic White Balance – here the camera is going to determine automatically what it believes is the temperature of the representative light. Given all the variables this often works surprisingly well but we’ll articulate below why it’ll seldom result in an accurate reproduction of the colors you saw at the time.
2. Pre-set White Balance – this option enables you to choose a specific setting that you believe will accurately reflect the light present. These options are going to usually include sunny, cloudy, shadows, tungsten, fluorescent, flash and night time. When you make your selection you are, in actuality, making a manual selection of a single Black Body temperature curve. Your selection will seldom match the circumstances exactly.
3. Custom Setting – this option enables you to use the camera to custom create a white balance. This is normally done by taking a photo of something gray in the given light conditions which will be used later as a reference.

Difficulty in accurately determining the source light of your photos leads to Inaccurate Colors

Achieving perfectly accurate colors in your photos is a significant challenge because, as noted:
• there may be more than a single light source in your photos in which case your camera has a hobson’s choice
• due to the complexity of the possibilities your camera may simply make the wrong choice, or
• your light source may be non Black Body and not fit the theory.
When the error in light source selection is large your camera will ‘rebalance” all of the colors in a drastic and awful way. In effect your camera generates what we refer to as an abnormal tint. What follows are samples of different lighting conditions and the photos the cameras produced, all exhibiting abnormal tint conditions. You will also notice how Perfectly Clear automatically corrected them.

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Having examined in depth thousands of images, Athentech Imaging’s conclusion is that the majority of abnormally tinted images are the result of your camera sensors capturing the image accurately and the Digital Sensor Processor [which contains a number of sophisticated algorithms] making a poor choice of “white” for balancing the image.

This results in the camera adding a significant color shift which manifests as a “color cast” or “abnormal tint” as shown in the foregoing photos. Please note that this can happen even if you, the operator, have appropriately selected a specific camera “white balance” setting, e.g. tungsten lighting.

Perfectly Clear goes beyond white balance to remove egregious Color Casts

To remove egregious color casts and better reflect the colors you saw at the time of shooting, Perfectly Clear incorporates a new patent pending approach to automatically identify an abnormal tint or color cast. Once identified, Perfectly Clear seeks to apply a more representative temperature of the light present for more accurate color reproduction. The results can be extremely good color corrections, all achieved by automatically detecting and removing the abnormal tint. Please note that the approach shown above is designed to search out and remove egregious color casts only. It has no dependence on white to function. It’s not a general replacement or substitute for the need for White Balancing. White Balancing, despite its drawbacks, is the state-of-the-art in cameras as we know them today.

RAW format can improve the colors in your photos by giving you flexibility in selecting a white balance different from the choice of your camera

By choosing to shoot RAW you’ll not be limited to the white balance chosen by your camera. This is one of many significant advantages to a RAW format workflow.

Competitive Comparisons

Except in the simplest of cases, photo “enhancement” tools and other automatic corrections do not address abnormal tints. “Enhancement” systems can’t robustly identify the abnormal tint so their adjustments tend to mischaracterize the problem and “enhance” the brightness of the photo exacerbating the distorted color in place.

These mischaracterizations of the problem is well evidenced in the following example photo:

Figure 26

Accurate color requires removal of Abnormal Tints

Perfectly Clear’s removal of an abnormal tint introduced by the white balance function of your camera reveals a more realistic representation of the colors and lighting you saw at the time of capture. The Abnormal Tint Correction in Perfectly Clear is seeking to ensure that the correction reproduces photos with true, accurate color … the Real Colors. Perfectly Clear can overcome your camera’s white balance limitation of egregious abnormal tints in your photos, a problem arising when you digital camera is seeking to add value to the photography experience by automatically white balancing your images. Unlike other photo “enhancements”, the Perfectly Clear correction operates to remove the abnormal tint in a manner consistent with how the human eye gathers light.

When a tint is successfully removed the results are Accurate Photos that match the original image in the mind’s eye and serve to preserve Precious Memories perfectly. Accurate Photos are Superior Photos and science shows superior photos have the greatest emotional impact with viewers.