Monday, 1 November 2010

Exercise 10: Colour cast and white balance

The first part of this exercise is to familiarise myself with the exact procedure for altering the white balance in my camera.

On the 400D there is a specific button that allows you to access the cameras white balance settings. There are eight altogether, auto, daylight (approx 5200K), shade, (approx 7000k), cloudy (spprox 6000K), tungsten light, (approx 3200K), white fluorescent light (approx 4000K), flash and custom.

The following settings are recommended  :-
  • Sunrise, although you can use AWB it is recommended that if possible use the custom white balance.
  • Midday, the Daylight setting is a reliable choice.
  • Sunset, the Cloudy white balance setting is a good choice.
  • Diffused light, on cloudy or foggy days, awnings etc again Cloudy is a good choice.
  • Flash, using the on camrea flash for use indoors or outdoors as a fill-in use the Flash option.
  • Tungsten light, this is the light most commonly found in household lights and lamps it produces a yellow/orange cast. Setting the cameras tungsten wb setting retains a hint or the warm colour of the tungsten light while rendering the colours accurately.
  • Fluorescent, commonly found in offices and public places this light ranges from a yellow to a blue-gree hue in these instances use the Fluorescent WB setting.
  • Other light, other types of lighting include mercury-vapor and sodium vapor found in public arenas and auditoriums, it is recommnded that in these situations you set a custom white balance.
If shooting jpeg only images you can use white balance auto bracketing which captures three images, each with +/-3 one stop differences in colour from the base current white-balance setting. This function is not available with RAW.

If you have a mixed light situation or less-than-perfect light you can set a custom white balance. In doing so you are telling the camera what should appear white in the specific light you are shooting in. As long as you remain shooting in those lighting conditions the custom white balance should render the whites accurately. This saves time that would otherwise be spent correcting colour cast post production.

To set the custom white balance on the 400D :-
  1. Position the camera so that a sheet of white paper fills the centre of the view finder, ensuring that it is correctly exposed.
  2. Press the menu button.
  3. On the Shooting 2 tab, press the down cross key and select Custom WB
  4. Press the Set button. Make sure the image displayed is that of the white sheet of paper.
  5. Press the Set button again, The camera then imports the white-balance data from the selected image.
  6. Lightly press the Shutter button to dismiss the menu, and then press the WB cross key. The White Balance screen will appear.
  7. Select Custom White Balance.
  8. Lightly press the Shutter button to return to shooting.
Information from the Digital Rebel XTi/400D Digital Field Guide.*

I need to find the four following outdoor lighting situations. Sunlight, Cloudy,Open shade on a sunny day, Auto. For each scene I have to choose a scene or object to photograph and shoot four versions using the four different white balance options.I then need to compare the results.

For the second part of this project I need to find and shoot a mixed-lighting scene. Suggestion made is to shoot a mixed indoor/outdoor shot at dusk. Shoot three versions using the following white-balance settings
  • Sunlight
  • Tungsten
  • Auto
Comparing the results which of the three versions would I choose? Experimenting in RAW find a compromise version that I like.

*refer to Lowrie C K (2007 p26/27 and p86-89) Digital Rebel XTi/400D Digital field Guide

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