  The energy range of hard X-rays is a key waveband to the study of high energy
processes in celestial objects, but still remains poorly explored. In contrast
to direct imaging methods used in the low energy X-ray and high energy
gamma-ray bands, currently imaging in the hard X-ray band is mainly achieved
through various modulation techniques. A new inversion technique, the direct
demodulation method, has been developed since early 90s. With this technique,
wide field and high resolution images can be derived from scanning data of a
simple collimated detector. The feasibility of this technique has been
confirmed by experiment, balloon-borne observation and analyzing simulated and
real astronomical data. Based the development of methodology and
instrumentation, a high energy astrophysics mission -- Hard X-ray Modulation
Telescope (HXMT) has been proposed and selected in China for a four-year
Phase-A study. The main scientific objectives are a full-sky hard X-ray (20-200
keV) imaging survey and high signal-to-noise ratio timing studies of high
energy sources.
