Removing a colour cast
When taking a picture, your iPhone or camera needs to make thousands of split second calculations, one of which is to judge how the scene has been illuminated – by sunlight, cloudy skies, tungsten bulbs, fluorescent tubes and so on – and take this into account when balancing the colours within the shot so the result reflects the original. If it gets it wrong, your image will have a blueish or yellowy tint, which you need to correct in post production.
When working with raw files in Lightroom, Aperture or Adobe Camera Raw, use the White Balance menu to select the original light source. These are described using plain English terms, like cloudy, daylight, shade and so on. If you’re not working with raw files you’ll have to use the Temp (or Temperature) slider in each application. This runs from blue at one end to yellow at the other; drag it away from whichever colour is tarnishing your image. If, for example, your picture has a yellowish-orange tint because it was taken under incandescent light, drag it towards the blue, and vice versa in the case of an alternative scenario.
This slider also makes an appearance in iPhoto, along with the eyedropper tool that lets you automate the process by clicking on a neutral grey (one that’s neither too hot or too cold) within the image. It will use this as a reference point, identifying any yellow or blue tint within the underlying colour and removing that from the whole frame.
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