Removing Colour Casts in your images : Understanding White Balance

Have you ever wondered why there are some instances that the images that you are taking has a different shade compared to the natural tones that you see? For example, it is a bright sunny day and you wanted to take a photo of someone who is blowing bubbles. In actual, you see the colour of her undershirt as grey. However, in the photograph that you have taken it has a yellowish tone or a blue!?! Now you are going to ask yourself, how come this happens? What should I do to make these pictures look natural? Well, the answer to all these questions is related to White Balance Setting.

Shade	Cloudy Setting
High colour rend fluorescent lamp	Direct Sunlight
Flash	Incandescent lamp

PHOTOGRAPHED BY: Cuchikoo; MODEL: Jameira Suansing

Everything that surrounds us has a light source; you would not be able to see anything without a light source. At home, there are the fluorescent lamps, and incandescent lamps. Outdoors we have the sun as a light source. But definitely, you would have noticed that these light sources have different colours. Normal domestic light bulbs are yellowish in colour and fluorescent lamps are white. In order to get natural colours in photographs, a colour adjustment must be done in the camera in order to compensate with the different light colours in the environment. Hence, the White Balance Setting. Colour Casts on images can be related to colour temperature. A wrong setting of white balance can result into a colour cast on the picture and this might be one of the things that photographers must avoid.

The White Balance is used to adjust the camera to provide natural looking photos or images to whatever light source available. White is the most neutral color and this colour is mostly affected by the light sources present. Colour adjustment is based on the white colour (that is why white balance is the term used in your camera). Colour temperature is measured by K (Kelvin). At 0 Kelvin, there is no particular heat energy from the object. White Balance was derived by using what they call the “Black Body Radiator”, which means when a particular object is heated it glows. The table below provides a list of light sources and its corresponding Kelvin.

Colour Temp	Light Source
1000 K	Candles, some flashlights
2000 K	Pre-sunrise
2500 K	Household Bulb/Domestic Energy Saving Bulbs (used)
3000 K	New Bulbs / some studio lights
3000 – 4000	Sunrise/Sunset (w/o smoke or heavy smog)
4000 – 5000	Flourescent bulbs, cool white – daylight balances
5000 – 5500	Electronic Flash, portable new bulb
5500 – 6000	Studio Electronic Flash new/Sunlight
6000 – 7000	Bright Daylight
7000 – 8000	Slight overcast skies at lower elevations
8000 – 9000	Heavy overcast / slight shade
9000 – 11000	Rain at lower elevations / clear day at higher elevations (above 8000 ft)
11000 – 18000	Overcast to snowy days at higher elevations (above 8000 ft)

 NOTE: ***Sunlight and daylight are different in colour temp, sunlight is light directly from sun about 5500 K, daylight is combination of sunlight and sky light and has a colour temp of 6300K (Source: “White Balance”. Photography for Beginners Vol. 01. Bournemouth. Dorset: Inagine Publishing. Copyright 2011. page 45)

I have asked several people regarding colour temperatures, all of them perceives blue as the coolest colour and red as the warmest colour (In my opinion, people associate the blue colour for water that is why we see this colour as cool. On the other hand, the red colour is associated with fire that is why it is perceived as a very hot colour.) It is the opposite for the Kelvin scale. Red is considered as the coolest colour and blue as the warmest. Cameras measure light according to RGB (Red, Green and Blue) colours. Technically speaking, in order to provide a basis for measurement, the Kelvin Scale is used by the camera for the White Balance. 

White balance adjustment is done by introducing the direct opposite of the colour cast in order to neutralize the strong colour. As an example, domestic light bulbs have a yellowish tint colour, a bluish cast is put in for adjustment to compensate and neutralize the effect. Human eyes does the same thing, humans do not realize that it happens because the human eye easily adjusts the balance for the surroundings. Since the camera is there to capture images and as much as possible it needs all the input that the photographer can provide thus, settings for the white balance is important.

WHITE BALANCE SETTINGS

All cameras have different settings and terms that it uses for white balance. It has a built-in Auto White Balance Settings. This setting acts like a pair of eyes for the camera. The camera gets an ambient reading from the light source and would base its adjustment on the reading that it gets. Auto settings is usually correct if there is a single light source in the environment, however, this is not the case for two or more light sources. Manual adjustment is introduced in the camera in order to correct White Balance. Commonly used terms for point and shoot cameras are 

1. Auto WB – all digicams have Auto WB setting but it doesn’t get it right all the time, always check
2. Tungsten – used under tungsten bulbs ; this can also be used if the photographer is aiming for a blue tone
3. Flourescent – this setting is suitable for indoor fluorescent lighting to combat yellow/orange tones from the light source
4. Daylight – this setting is ideal for outdoors in open sunlight and no sunshade
5. Flash – this setting is ideal for studio work; this is to prevent blue tones that are coming out of the flash bulbd
6. Cloudy – this setting is suitable outdoors when there is an overcast of clouds to give images some warmth

Each of these settings has a different symbol in the cameras and would compensate for the shooting conditions available. 

For serious photographers and those who own a DSLR Camera it is a different story, the concept of white balance is the same for all cameras but settings are much broader and complicated. Since I have the Nikon D90, I am going to use it as an example in this article. Another important note, if you have a RAW format setting in your camera, then it is best to use that format. Post adjustment on the images can be done for White Balance using the RAW format without affecting the quality of the image (see the article “Understanding your picture formats: RAW vs Jpeg")

The Nikon D90 has 9 White Balance Setting. Out of that 9, in the Flourescent settings there is another 7 settings that the user can choose from. Provided below is a list of these settings and its use.

1. Auto – best for most circumstances, camera takes ambient (present/existing) light and makes colour adjustment
2. Incandescent – standard household light bulb
3. Fluorescent – coming from a fluorescent type lamp     

7 types of Fluorescent Settings in Nkon D90

a. Sodium Vapour – found in street lights, parking lots, and sports arena, emit deep yellow colour

b. Warm-White Fluorescent – white light with a bit of amber cast to add some warmth in the scene at 3000K similar to incandescent

c. White Fluorescent – casts a neutral white light at 3700K

d. Cool White Fluorescent – cooler than white fluorescent at 4200K

Day White Fluorescent – approximates sunlight at about 5000K

e. Daylight Fluorescent – same colour as daylight 6500K

f. High temp Mercury Vapour – vary in temp depending on manufacturer between 200K to 7200K

4.       Direct Sunlight – outdoor setting in the sunlight
5.       Flash – built in Speedlight, hot-shoe speed light or external strobes
6.       Cloudy – overcast skies
7.       Shade – shade of trees or a building or under an overhang or a bridge, any place where the sun Is out but is blocked
8.       K – Choose Colour temp
9.       Preset Manual

There are two settings in the camera wherein an input is needed from the photographer. This is the K setting and the Preset Manual Setting. The K setting is used to choose the right colour temperature based on the Kelvin Scale. The colour temperatures range from (2500 [red] – 10000 [blue]).

 Source: Thomas, J. Dennis. Nikon D90: Digital Field Guide. 

Indianapolos, Indiana: Wiley Publishing Inc., Copyright 2009 page 82

A table was provided above regarding the measurement of light sources based on Kelvin temperature. It would be helpful to read and understand that table if the photographer would be using the K setting. On the other hand, it is a different story for the Preset Manual Setting. This setting is based on a neutral object to measure the white balance. Neutral colours are grey and white. The figure below shows the White balance fine-tuning grid that the Nikon D90 has.

 Source: Thomas, J. Dennis. Nikon D90: Digital Field Guide. 

Indianapolos, Indiana: Wiley Publishing Inc., Copyright 2009 page 81

HOW TO CALIBRATE YOUR CAMERA FOR WHITE BALANCE

Normally, in order to get the right white balance manually, the camera is introduced to a photographer’s grey card. The grey card is completely neutral at 18% LTF (***18% LTF Australian Standard; Light Transmission Factor – the darker the percentage the lighter the shade), this shade reflects all colour equally. If you do not have a grey card, a white sheet of paper can also be used to calibrate the camera. Take an image under the lighting source with your grey card or paper, and check your camera. Review the image and check which setting is appropriate for the environment until you get the natural colour that you are aiming for. For Auto White Balance settings, the camera will do calculations and apply the correct white balance on the other images that you would be shooting at these conditions.  It is important that once in a while you calibrate your camera in order to balance the images in different conditions. Repeat the process if you are under a different condition in order to make sure that the correct balance is achieved all the time.

There is another way to calibrate the white balance setting. This is through the use of an Expodisc. An expodisc is an accessory that can be attached in front of the lens like a filter. The lens is pointed at the light source and the camera would automatically adjust it to the correct colour temperature. Before using the expodisc, the camera must be set to Preset Manual or Custom White Balance Setting.

REFERENCES:

1.       Sparks, Jon. Nikon D90: The Expanded Guide. East Sussex, Great Britain: AE Publications Ltd, Copyright 2009.

2.       Thomas, J. Dennis. Nikon D90: Digital Field Guide. Indianapolos, Indiana: Wiley Publishing Inc., Copyright 2009

3.       Ang, Tom. Digital Video: An Introduction. London, Great Britain: Sands Publishing Solutions, Copyright 2006

4.       Cope, Peter. Get The Most From Your Digital Home MovieMaking. Cincinnatti, Ohio: David & Charles, Copyright 2007

5.        “White Balance”. Photography for Beginners Vol. 01. Bournemouth. Dorset: Inagine Publishing. Copyright 2011. page 42 - 46