We propose an experimental and theoretical methodology
based on spectroradiometric procedures to determine the
spectral sensitivity of digital still cameras (DSC). The
opto-electronic conversion spectral functions (OECSF's)
are obtained from normalized digital level (NDL) vs.
spectral exposure data, fitted by a typical sigmoidal
transition curve. At this stage, we define spectral
responsivity r(λ, H) and action spectrum a(λ, NDL), which
are conceptual derivations of the general concept of
spectral sensitivity of any image sensor. Then, the real
spectral responsivity and action spectrum are represented
as 3-dimensional functions, where r(λ, H = constant) and
a(λ, NDL = constant) profiles are scaled relatively to
determine the valid linear output range of the digital
image capture device. This range would serve to design
the colorimetric profile of the camera with CIE-1931 XYZ
standard observer, which is considered as a linear color
image sensor.This research was supported by the Comisión
Interministerial de Ciencia y Tecnología (CICYT) (Spain)
under grants TAP96-0887 and TAP99-0856
