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Digital images generally consist of a mixture of the three primary colors: red, green and blue. For various reasons you can read about in-depth elsewhere, the red, green and blue values which serve as the starting point in any raw photo development program need to be corrected in various ways before they resemble the scene photographed. One of those corrections is based on setting the correct white balance - making things which should be white (or neutral gray) appear white (or neutral gray), otherwise they will have a color cast. White balancing works by multiplying each of the color primaries by a different amount, until you get a satisfactory result. In order to make this operation more human-friendly, the multipliers are controlled by easier to understand temperature and tint sliders (and a red/blue equalizer for photos taken in unusually 'cold' or 'warm' environments - read about it below), and you can have them automatically set the correct values by using the "Spot WB" pipette on an area of the photo which should have a neutral color.
Having an incorrect white balance gives the image a color tint, typically warmer (orange), or colder (blue). Some people use this for creative effect. There are various tools and operations which rely on the assumption that the white balance of the image is correct, for example highlights recovery, skin or sky hue targetting, etc. You should not make creative color tints using the white balance tool, but rather use it for making white what should be white, and then use any of the other tools in RawTherapee to add a desired color tint for creative effect.
White balance can be set in different ways: Camera, Auto, Custom, or a host of presets for different light sources.
- Takes the white balance used by the camera. If you shoot only in raw (so no raw+JPG), put the white balance settings of your camera on Auto. This should generally give good results.
- Automatically corrects the white balance, by assuming that the average color of the scene is neutral gray. Works well for a wide range of scenes, and can be a good starting point for manual adjustments.
- Set your own color temperature and green tint by moving the two sliders and/or using the Spot WB tool.
When you click on the Spot WB button File:Gtk-color-picker.png (shortcut: w), the cursor changes into a pipette when it's over the preview. Click on a gray or neutral area to determine the correct white balance. The gray/neutral area may not be clipped, otherwise readings will be off. You may use the picker several times on different places in the photo, until you find a spot that leads to a suitable reading. Use the Size drop-down box to change the size of the pipette. This tool can be used as well inside a detail window. Right-click to cancel the tool and to get the regular cursor back.
Temperature and Tint
Moving the Temperature slider to the left makes the image cooler (bluish), moving it to the right makes it warmer (yellowish). Moving the Tint slider to the left makes the image purplish, moving it to the right greenish.
Allows to deviate from the normal behavior of "white balance", via increase or decrease of the ratio between red and blue. This can be useful when shooting conditions are far from the standard illuminant (e.g. underwater), or are far from conditions where calibrations were performed, where the matrices or ICC profiles are unsuitable.
White balance connection to exposure
The white balance is described in temperature and tint, but will for raw images internally be translated into weights of the red, green and blue channels. The weights will be adjusted so that the channel with the smallest weight reaches clipping in the working space (usually ProPhoto RGB) when the raw channel is clipped. In other words, with exposure set to 0.0 and no highlight recovery enabled the full visible range is fully defined by the raw backing. As white balance changes the weights you may see a slight exposure change if you make drastic changes.