Saturday, 27 August 2011

Exercise - Judging colour temperature 1

The colour of light varies and this is known as its temperature. As this is a scientific term it is related to the temperature that light is produced by the sun at , and, somewhat counter intuitively, the bluer the light the higher the temperature. We are attuned to light, and our brains 'see' light as the colour wee expect it to be, usually at midday, in the summer. Even when the light is a noticeably different colour to this we still 'see' it as this average colour, and have to concentrate to see differently. 

This is further complicated in my case, As with many other people, in that I where glasses that have lenses that vary in sunlight (photochromic), however these do not just cut down the amount of light but are also often coloured, in my case brown, rather than a neutral gray. I get used to seeing though these lenses and my brain interprets this view of the world as the 'correct' one. When in shade they are virtually clear, while in bright sun almost black (with a  brown tinge) - so colours tend to look very intense with the glasses on , and much less intense and slightly bluer with the glasses of.

The camera lenses 'sees' and therefore records in a neutral fashion - so if the colour of the light changes this is recorded by the camera. This can be very obvious with a film camera, but with a digital camera the internal software can compensate for this and  average the recording out (auto - white balance, AWB). The camera can also be set to compensate for specific types of light such as cloud, or shade. The accuracy of the settings will vary with the camera. This can further be varies by the type of files you take - if you use RAW files the RAW editing software again gives you a chance to change the settings for the type of light both via presets and intuitively via sliders.

In this exercise images were taken on the 'daylight' setting in the camera and not altered afterward. I took images of my husband and daughter, both were bribed into doing this. They were taken within a couple of days, the full sun and shade photos on the same day, and the other a few days later, in the south of England.

Full Sun.

ISO 100, f/5, 90mm efl, 1/1000 sec

Very bright sunlight, although with a cloudy sky. The colour appears neutral. The white t-shirt looks white, with slightly bluish shadows.

ISO 100, f./5, 90mm efl, 1/1600 sec

Again very bright sunlight, with neutral colours ( and a grumpy teenager).


ISO 100, f/14, 90mm efl, 1/60 sec

This was in deep shade under a tree. The shutter speed has dropped from 1/1000 to 1/60. The colour of the image is much bluer generally, with slightly blue shadows in the t-shirt. 

ISO 100, f/7.1, 90mm efl, 1/200 sec

Again a picture in deep shade under a tree, the skin her has a markedly bluer tone to it.


ISO 160, f/8, 1/60 sec.

This image was taken with a different camera, fairly late in the evening, with a low sun. The colour is definitely much more orange, and gives an unnatural skin tone.

ISO 200, f/8, 1/60 sec.

Taken at the same time as the picture above, but my daughters skin looks more natural because it has an olive tone.

Even though I was consciously looking for colour changes when I was taking these images they were not as visible as I would have expected. This was particularly true of the sun versus shade images, where I had to think to recognise the colour change. It was easier to see in the evening light - but I expect that to be orange.

Learning points.
  1. Think about colour and the time of day
  2. The mind fools the eye
  3. Cameras don't lie ( but can compensate without you being aware of it)
  4. AWB might not be the 'best' setting - depending on what is wanted.

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