  The measurement of photon-number statistics of fields composed of photon
pairs, generated in spontaneous parametric down-conversion and detected by an
intensified CCD camera is described. Final quantum detection efficiencies,
electronic noises, finite numbers of detector pixels, transverse intensity
spatial profiles of the detected beams as well as losses of single photons from
a pair are taken into account in a developed general theory of photon-number
detection. The measured data provided by an iCCD camera with single-photon
detection sensitivity are analyzed along the developed theory. Joint
signal-idler photon-number distributions are recovered using the reconstruction
method based on the principle of maximum likelihood. The range of applicability
of the method is discussed. The reconstructed joint signal-idler photon-number
distribution is compared with that obtained by a method that uses superposition
of signal and noise and minimizes photoelectron entropy. Statistics of the
reconstructed fields are identified to be multi-mode Gaussian. Elements of the
measured as well as the reconstructed joint signal-idler photon-number
distributions violate classical inequalities. Sub-shot-noise correlations in
the difference of the signal and idler photon numbers as well as partial
suppression of odd elements in the distribution of the sum of signal and idler
photon numbers are observed.
