How to Color correction for setting custom white balance in DSLR Camera : Video Series

Color is a visual property of perception.  Camera chip interprets the light that passes through the lens in a similar way as our brain interprets the light passing through our eyes.

Our perception of color is a result of the journey undertaken by light. Light travels from the light source onto an object and then it bounces off the object and continues to travels through our eyes onto receptors. Then information received is processed by the brain.  The brain, being very considerate of our psyche, it balances the color of the light to a white point (simulating daylight).

The camera works in a similar manner as the human eye + brain: the light enters the lens and falls onto sensor and then the data gets processed and the software/firmware assigns corresponding values based on camera setting. Color is determined by many variables, the main ones are: 

1. The Light source:

Human beings on planet earth have been exposed to the single light source called the Sun for millions of years. The first time humans where able to produce an alternative light source (fire), according to the most recent study, was about 790,000 years ago (oh yeah, check out our previous tutorial on photographing fire)

Then in the early 19th century, an incandescent light bulb came into existence, followed by fluorescent tube by the end of century, followed by halogen bulb, and flash tubes around 1930s. It is fascinating, to me, that the human brain has the ability to automatically tweak any light source to a white point. This is why people are able to observed the environment around them without any dramatic change. If our brain was set to a fixed white balance setting, Thomas Edison would have died as poor man.

Sun
The color temperature of the sunlight on a clear day generally varies from 2000 degrees Kelvin at sunrise to 5400K  by noon and back to 2000 degrees at sunset while in the shade color temperature stays at about 8000 degrees. As human brain itself is set to (AWB) automatic white balance we do not notice the change so dramatically.

Incandescent bulbs (the famous clamp lamp) project the light at color temperatures ranging from 2650 K to 3200 K degrees, depending on wattage
Flash Strobe projects light at 4800 to 5500 – depending on the brand and power settings. High end professional strobes maintain the same color temperature of 5400 K (daylight)   at any power setting.

2. Substances the Light Goes Through Before It Hits the Object.

For example, the sun emits the light at 5780k. That light then passes through layers of gasses of the atmosphere and clouds and changes to the color from 2000 to 30000 K. With artificial light sources color or color-correcting gels can be used to alter the temperature of the light.

3. Properties of the Object.

Texture determines how much light is being absorbed and how much light will bounce off a surface. While pigments and other properties determine the wavelengths of the bounced light and thus determines the color in a spectrum.

4. The substances that light goes through on the way from the object to the eye (or lens).

When photographing outdoors there are various factors that can alter the color such are Haze, Evaporation, Humidity, and Air pollution (in big cities). This can be further adjusted by on lens filters. A “UV” filter is most commonly used.

5. Type of lens and its quality.

Better quality (more expensive) lenses allow the light to travel through the glass without farther fogging or softening and provide additional filtration of ultra violet light.

6. Receptors / Digital Sensor.

When the light finally passed through our eyes receptors pass the information to the brain. About 5% of population (mostly males) lack certain receptors and are blinded to certain colors.

7. Brain / Computer:

Our brain processes information received and balances colors to a white point. It can also alter some colors and saturation if it is under the influence of psychedelic substances….oh good old days…. On a computer or in camera the data that corresponds to color can be altered by the camera settings or if shooting RAW by raw processing software or pixel editor (such as Photoshop)


Watch and learn .....

Related Article Photography and white balance

Conclusion:

Since many variables influence the color of light, the light temperature will vary and be inconsistent and thus camera’s automatic white balance or predetermined settings (daylight, shade, florescent, incandescent etc..) might not provide accurate results. Custom White Balance allows the photographer to tell the camera, what is in truth, the white point.

Video by Robert Grant. Article by Sasha Gitin from http://www.learnmyshot.com/