Category: Foundations
Digital Number (DN)
A digital number (DN) is the raw pixel value recorded by a sensor before it is converted to physical units like radiance or reflectance.
Also known as: DN, raw pixel value
Expanded definition
Most sensors record pixel values as digital numbers (DN). DN values depend on instrument settings, bit depth, and calibration. On their own, DN values are not comparable across sensors and are often not comparable across processing versions.
To make imagery physically meaningful, DN values are calibrated to radiance and often further converted to reflectance.
If a workflow mixes DN-like inputs with reflectance-like inputs, indices and thresholds become unstable.
Related terms
Radiance
Radiance is the raw physical quantity measured by optical sensors, representing energy reaching the sensor.
Reflectance
Reflectance is the fraction of incoming light that a surface reflects, commonly used for analysis and comparison.
Radiometry
Radiometry is the measurement and calibration of electromagnetic energy recorded by a sensor.