A technique that makes diagonal and curved lines in digital images look smoother. Pixels are square, so such lines can look like small steps, often called "jaggies". Anti-aliasing adds pixels of in-between tones along the edges to hide these steps.
In cameras, the term also refers to an anti-aliasing filter, also called an optical low-pass filter. It sits in front of the sensor and slightly blurs fine detail to reduce moiré. Some cameras leave it out to get sharper images.
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