The ERGAS parameter for measuring synthesis error

The ERGAS is a commonly used parameter to assess the quality of images resulting from the synthesis of images at a higher spatial resolution by exploiting one, or more, alternate high-resolution image acquired in another modality. When the higher resolution image is panchromatic (Pan), i.e., a single wide spectral-band image acquired across the visible and possibly near-infrared (NIR) wavelengths, this fusion process is often called pansharpening of multispectral images.

The ERGAS has been first proposed by Wald (2000) but has been termed ERGAS by Wald only in 2002. ERGAS is the acronym for "erreur relative globale adimensionnelle de synthese" in French, which means relative dimensionless global error in synthesis.