Final answer:
The technique used to convert a color image to black and white is adjusting the saturation.
Step-by-step explanation:
The technique used to convert a color image to a black and white image is adjusting the saturation. When the saturation is reduced to zero, the image becomes completely desaturated and appears as black and white. This is because saturation represents the intensity or purity of colors in an image, and reducing it removes all color information.
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