Tuesday, 25 October 2011

Exercise: Colour cast and white balance

In this exercise we are exploring the varying colour temperatures given off by the sun in different circumstances such as time of the day, clouds, shade, sunshine and the interaction with artificial lighting. A key point I want to note is that although temperature increases with heat (degrees kelvin) the 'colour cast or colour temperature' of blue (around 10,000k) is a higher temperature that that of a setting red sun (3000k), and white light (12 mid day in sunshine) being somewhere in between the two at 5500k. An interesting comparison made in the notes was certain elements as they increase in temperature turn from red to white to blue.

We are to find scenes in sunlight, shade on a sunny day and cloud and take four images of each with the camera set for white balance settings of auto, sunlight, shade and cloud noting the difference.

The first set of four images were taken on a cloudy day.

I chose these coloured pegs as I thought varying settings would make a difference but there is very little. If anything the Cloudy setting is less intense and therefore probably more true  in terms of colour but I like the brighter more intense colours of the Shade WB.

The next set were of those in sunlight, taken at around 11 am in early Autumn.

Again the relevant setting seems to be more accurate, that is the daylight setting, or sunlight setting does not have a red'ish cast compared to the others, albeit warming up the scene nicely. As it can be seen although the sun was shining there were clouds about and the Cloudy setting has also worked reasonably well, perhaps better than the Auto setting.

The final set were taken on a sunny day in the Shade or part shade. Here there are seen more dramatic differences.

The Auto setting definitely has a blue cast to it and is not the best version by far. I was surprised to see that the Shade version has tried to compensate for the Blue Cast but warming up the image, but a little too much, almost as it it were in sunshine itself. The Cloudy WB probably reflects the most accurate and pleasing image here.

The second part of this exercise is to take three images using a white balance of auto, sunlight and tungsten at dusk where both the inside and outside are visible with the interior lit by incandescent (tungsten) lighting. This required a tripod as the shutter speeds were around 1/4 second.

The daylight setting certainly has warmed up this image, a little too much though. The auto setting has too warmed up  the image but not quite as much. The tungsten setting has good neutral inside tones but at the cost of producing a blue cast to the outside particularly on the edge of the panes of glass.

Finally we are asked if using RAW to look at adjusting the white balance sliders to see if there is a compromise. If found that by adjusting the temperature from 3150 to 3400 and the tint from +4 to -12 gave the best results. This would warm up the image and increase the green of the background foliage respectively.

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