White Balance Corrections in Adobe Photoshop Lightroom 2
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White Balance tool
The White Balance tool is located near the top of the Basic panel (Figure 6.25). You can activate the tool by clicking it (or press 
), which unlocks the tool from its location and allows you to click anywhere in the image to set the white balance. The floating
pixel magnifier provides an extreme close-up of the pixels you are measuring, which can really help you select the correct
pixel reading. As you hover over an image, you see the RGB readout values for the point in the picture beneath the cursor
(Figure 6.26). These RGB readings are shown as percentage values and can help you locate and check the color readings (if the RGB values
are all close enough to the same value, the color can be regarded as neutral). If the Auto Dismiss option is disabled, you
can hold down the key and continue clicking with the tool until you get the right balance setting, while the 
key can be used to cancel and return the tool to its normal docked position.
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- To make a white balance adjustment, select an area of the picture that should be neutral in color (but not a bright white area of the photo). The light gray stones in this picture are a perfect spot to sample from. If the Auto Dismiss box (circled) in the toolbar is checked, the White Balance tool automatically returns to its docked position in the Basic panel. If the Auto Dismiss box is unchecked, you can click and keep clicking with the White Balance tool until you are completely satisfied with the white balance adjustment that you have made.
- The Show Loupe check box allows you to toggle displaying the loupe that appears just below the White Balance tool cursor. You can adjust the loupe scale setting by dragging the slider next to the Show Loupe item in the toolbar. This slider adjusts the sample grid pixel size, and dragging the slider to the right will increase the number of pixels used when sampling a white balance point measurement. Increasing the pixel sample size can be beneficial if you want to aggregate the pixel readings more, such as when you’re sampling a really noisy image and you don’t want a white balance measurement to be unduly affected by the pixels that contain color noise.
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To apply an Auto White Balance, you can also use the 
(Mac) or 
(PC) keyboard shortcut.
White Balance corrections
In most shoot situations, once you have found the right white balance, all the other colors will tend to fit into place. The As Shot camera Auto White Balance setting may do a good job, but it really depends on the camera you are using (Figure 6.27). Even the best camera won’t know how to handle every lighting situation it meets. In Figure 6.28, we see a scene where there were mixed lighting conditions. This photograph could be processed for either the daylight lighting or the tungsten lighting indoors, and each could be said to be correct. In situations like this you can’t always rely on the camera’s Auto White Balance setting; you have to decide for yourself which setting looks the best. This is where the White Balance tool can come in handy. The trick is to analyze the picture and look for colors in the scene that should be a neutral, nonspecular, textural highlight. You should try to select a neutral light gray, because if you select a white that is too bright, there may be some clipping in one or more of the color channels, and this can result in a false white balance measurement and adjustment.
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Understanding White Point
The White Balance slider controls in the Basic panel have the greatest impact on the color appearance of an image (Figure 6.29). The numbers used in the Temp slider refer to the temperature scale measured in degrees Kelvin, which in photography is commonly used when describing the color temperature of a light source.
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Artificial lighting, such as a tungsten lamp light source, has a color temperature of around 2800–3200 K, whereas average daylight is notionally rated as being 5000 K and overcast daylight is somewhere around 10000 K. Photographers often describe higher color temperature lighting conditions as being cooler and the lower color temperature lighting conditions as being warmer, because most people equate blue colors with coldness and reddish colors with warmth (although technically speaking, a bluer color temperature is actually hotter). The Temperature slider scale allows you to set what “should be” the white point of the image based on the Kelvin scale. The key point to emphasize here is that the White Balance controls are used to “assign” the white point as opposed to “creating” a white balance. Some people get confused on this point because they assume that if 3200 K equates to tungsten-balanced film and 5500 K equates to daylight-balanced film, they wrongly expect that dragging the Temperature slider to the right makes the image cooler and dragging to the left makes it warmer. The opposite is true, because you are using the Temperature slider to assign a color temperature to the image. Dragging the slider to the right will make the image warmer and dragging to the left will make it cooler. Try thinking of it this way: If you have a photograph shot under average daylight conditions and assign the image a lower color temperature more suited for tungsten lighting conditions, such as 3200 K, then naturally enough, the colors in the image will appear blue. This is the same as using a tungsten-balanced film emulsion to record a daylight scene.
Tint adjustments
The Tint slider adjustments can usually be quite minor, except for those situations where the light source emits uneven spectral wavelengths of light, such as when shooting under fluorescent lighting. It is hard to set an accurate white point for these types of lighting conditions, but fluorescent lighting conditions will usually require a heavy magenta tint bias to the white point to remove a green cast.