  Incoherently illuminated or luminescent objects give rise to a low-contrast
speckle-like pattern when observed through a thin diffusive medium, as such a
medium effectively convolves their shape with a speckle-like point spread
function (PSF). This point spread function can be extracted in the presence of
a reference object of known shape. Here it is shown that reference objects that
are both spatially and spectrally separated from the object of interest can be
used to obtain an approximation of the point spread function. The crucial
observation, corroborated by analytical calculations, is that the spectrally
shifted point spread function is strongly correlated to a spatially scaled one.
With the approximate point spread function thus obtained, the speckle-like
pattern is deconvolved to produce a clear and sharp image of the object on a
speckle-like background of low intensity.
