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Color Temperature & Color Rendering Index DeMystified


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Human Eye vs Camera White Balance
We humans are lucky. Our eyes adjust automatically to subtle changes in brightness, as well as differences in the color of light sources we may find ourselves in. For example, if you walk indoors to a warm-lit living room from a dusk exterior where everything was lit cool blue, your eyes will adjust to the differences in brightness & color almost instantly. The change will be largely imperceptible to you when it happens.

So our eyes adjust to these differences automatically, but how do todays digital cameras deal with them? While continuing to get better, they still aren't quite so lucky. Most digital video & still cameras have the ability to automatically set both exposure and white balance, self-adjusting them on the fly as lighting conditions change. If a camera is set to Auto-White Balance, it will search the image for something it perceives to be white, lock on it, and then adjust all other color renderings in the image based on that decision. And yes, in this mode cameras can be fooled. So their auto-exposure / auto-white balance imaging sensors & circuitry do a clumsier job of adjusting to both brightness & color changes in lighting conditions than the human eye. And if the adjustments happen while you are shooting video, those auto-adjustments can be recorded & visible to the viewer in playback.

A less potentailly distracting option than auto-white balance is available, but it isnt as versatile in dealing with the subtleties of real world lighting. We are talking about the camera's Preset White Balances, which are factory default settings for the accepted standards of the most common lighting environments.

These installed presets are created based on the color reflection information of a white (or neutral gray) object, lit by the selected color source (exdaylight, or tungsten-halogen).

Note - Film stocks are created using the same concept, manufactured with emulsion color balances that anticipate being used in standard tungsten or daylight environments.

Using Camera Preset White Balances
All digital video & still cameras will have Daylight & Tungsten presets, some will also have Fluorescent, and Cloudy Sky settings. Most still cameras will have a preset for Electronic Flash, which is basically the same as daylight. Selecting a preset white balance that fits the type of light being used can give generally pleasing results, and can be a popular choice when you are working quickly. However using a preset that is different from the color temperature of your lighting can give pretty inaccurate results, as some of the following photos will show.


Cameras and Colors of Light
4 photos to show how camera white balance presets deal with color temperatures. Notice the color of the white card in each image.

Outdoors on a sunny day with the daylight preset on the camera.

Generally accurate, and a great choice if you're working fast.

Outdoors on a sunny day, but with the camera set to tungsten white balance.

The camera expects the warmer 3200K but is getting the cooler 5600K.


Indoors, in a tungsten light filled room.

The camera is set on tungsten white balance.

The ambient lighting in the room is still tungsten, as is the white balance setting.

However, the dominent lighting of the shot is now the daylight color of the camera's electronic flash.



Storing Camera White Balances
The real world doesn't always offers us ideal scenarios. We can often find ourselves in lighting environments that fall outside the confines of the camera presets, either for practical or creative reasons. Such as:
  • The color temperature of the light source you are shooting in is different than the color of the preset (a scene lit only by blue sky with no direct sun may have a color temperature closer to 6500°K than the Daylight preset of 5600°K).
  • You are shooting in a room with several different light sources, thus a mixture of color temperatures.
  • The creative needs of your production may require a different color mood than the standard rendering that the camera presets will provide.
  • To move outside the confines of the Presets, you will need to store your own white balance. When storing a white balance, you should place a white or neutral gray card in the key (main) light of the scene, place the camera on auto exposure, and fill the image frame with the lit card before hitting the white balance button. Note - it is important that the camera be set to auto exposure, to avoid overexposing the white card. If overexposed, the camera will not read the color of the light on the card accurately. Note - Some cameras have a 'tunable' white balance where you can dial in the desired color temperature you want the camera balanced to. For an experienced user, this can bring increased creative options.



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