  Experimental data with digital masks and a theoretical analysis are presented
for an imaging scheme that we call time-correspondence differential ghost
imaging (TCDGI). It is shown that by conditional averaging of the information
from the reference detector but with the negative signals inverted, the quality
of the reconstructed images is in general superior to all other ghost imaging
(GI) methods to date. The advantages of both differential GI and
time-correspondence GI are combined, plus less data manipulation and shorter
computation time are required to obtain equivalent quality images under the
same conditions. This TCDGI method offers a general approach applicable to all
GI techniques, especially when objects with continuous gray tones are involved.
