Tuesday, 3 July 2012

Judging Colour Temperature

Exercise -  Part 1 - 3 images Part 2 - 9 images

Part 1
One of the reasons I always shoot images in RAW format is so that I can correct or adjust elements post capture e.g. white balance (WB) or exposure. As I know I can make adjustments later I tend to leave my camera WB setting on "auto". Nine times out of ten I would say the camera records the scene accurately and I leave the image WB as shot.

Reading the course material on colour temperature and around the subject in "Light, Science and Magic"  the subject becomes quite scientific discussing electromagnetic radiation and wavelengths. I think in terms of my photography it's sufficient for me to understand the following:
  • colour temperature is measured on the Kelvin scale.
  • for photographic use daylight is 5500 Kelvin.
  • higher numbers contain more cool colours.e.g. 10,000K light is quite blue.
  • lower numbers err towards red/yellow colours.
The visible wavelengths are the colours of the rainbow with blue wavelengths shorter than red. This is why the sky takes on a red/orange tint at sunset because the short blue wavelengths are more easily scattered in the atmosphere than the longer red which are then more visible. Sunlight at midday is colourless because the full range of visible wavelengths are present.

For the first part of this exercise using a camera WB setting of "daylight" take 3 images,  one in the middle of the day in sunlight, another at the same time in shade and finally another at the end of the day when the sun is close to the horizon. Compare the images.

Image 1
Taken in the middle of the day in bright sunlight this image has high contrast but it appears exactly as I remember the scene.

Image 2
Taken in the shade this image also initially appeared to represent the scene as I recall it at the time. Comparing it to the image above afterwards I would say it appears cooler than the "neutral" white balance I remembered.

Image 3
Taken at the end of the day.
(image to follow)

I am expecting the image taken at the end of the day to have a warmer WB than the others which is a result of the light reflected from the sky. The image taken in the shade has less contrast than the full sun image and also a slightly cooler tone.

The camera records the differences in these circumstances quite distinctly and much more than our eyes do as they adjust to the variations in light very quickly. Being aware of the way the camera's WB setting can affect an image when combined with the actual light at the time is another important tool for a photographer to learn to use.

The second part of this exercise is to take a series of pictures but in this case adjust the WB in camera. So in each set of 3 below, one has been taken in auto WB, another sunlight/daylight and the third WB shade.
Compare the images.

Series 1

In this first set of three the auto WB image at the top is closest to my recollection of the colours at the time. The sunlight WB is acceptable but the shade WB image is far too yellow and the colours are unrealistic.

Series 2

In this second series of images it is more difficult to differentiate between the auto WB and the sunlight WB. This is probably because of the variety of deeply saturated colours in the scene which would make either image acceptable. Of the two I prefer the sunlight WB (centre) as the colours of the white flowers are more realistic. Again the shade WB is too yellow.

Series 3

I think it is in this final series of three images that you can see the effect of changing the camera's WB most clearly. The auto WB has recorded the scene quite accurately. The sunlight WB has an overall blue tone and the shade WB has a yellow tone. In this case auto and shade WB are more accurate.

Comparing the results of this exercise has demonstrated how selecting the WB to suit the conditions at the time is important. Selecting the incorrect WB can result in quite a strong colour cast. However it is always possible there may be some creative decision behind using an "incorrect" WB. Generally the auto WB setting does a reasonable job. However I will continue to shoot in RAW format so that I can make adjustments later for the following reasons.

Personally I find reviewing an image in camera difficult. The size of the LCD screen for starters makes it impossible to view colours in any detail and when out in the field the images will be viewed in the ambient lighting conditions which will also have an effect on how it appears. Shooting in RAW format means that I have full creative control over the images.

Although I would be reluctant to rely solely on in camera WB settings, through comparing the results of this exercise, have a better understanding of why it is something to be considered at the time of shooting. 

1 comment:

  1. very nice instruction with picture's example, i am fond of taking photos, and collecting information about photography and art, i just want to say thanks for sharing this great post.

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