Signal-to-noise ratio

Signal-to-noise ratio compares a desired signal with unwanted background variation. It may be expressed as a power ratio, an amplitude ratio, or in decibels.

Decibel: A logarithmic unit that expresses ratios of power or amplitude, commonly used for sound and signal levels. Decibels make very large or small signal-to-noise ratios easier to express.
Image noise: Unwanted variation in image brightness or color that obscures scene details. Image quality often depends on whether detail stands above sensor and photon noise.
Signal: A varying physical quantity that carries information about a source, event, or message. The numerator is the part of a measurement meant to carry information.
Contrast-to-noise ratio: A measure comparing the difference between two signal levels with background noise. It emphasizes distinguishability between image regions rather than signal relative to noise alone.
Shot noise: Statistical fluctuation arising from the discrete arrival of particles such as photons or electrons. It creates a fundamental floor that stronger signals can reduce only in relative terms.
Noise power: The average power carried by unwanted random fluctuations in a signal or measurement. Noise power supplies the denominator when the ratio compares signal and noise power.
Radio astronomy: The study of celestial objects through radio waves emitted or reflected across the universe. Astronomers use the ratio to decide whether faint emissions stand above receiver and sky noise.
Measurement noise: Random or systematic variation in a measured value that does not represent the quantity of interest. This broad category includes the fluctuations treated as noise in the ratio.
Signal-to-interference-plus-noise ratio: A ratio of desired signal power to the combined power of interference and noise. It explicitly includes competing signals that a basic noise-only denominator may omit.
Thermal noise: Random electrical noise produced by thermal agitation of charge carriers in resistive components. It sets a temperature- and bandwidth-dependent limit for many electronic measurements.

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