  In some super-resolution techniques, adjacent points are illuminated at
different times. Thereby, their locations and light intensities can be detected
even if the images are very blurred due to diffraction. According to
conventional theories, the points' inner details cannot be recovered because
the images' high frequency components are removed due to the diffraction-limit.
But this study finds an exception, and full information can be extracted from a
diffraction-blurred image. In such a "resolvable condition", neither profile
nor detail information is damaged by diffraction. Thereby, it can be recovered
reversibly by solving equation systems in spatial domain or frequency domain.
This condition is tightly relevant to the imaging condition of existing
super-resolution techniques. Based on the condition, a method is proposed which
can achieve unlimited high resolutions in principle, and its effectiveness is
demonstrated by both theoretical analysis and simulation experiments. It can
also work without any observed image outside the region of interest. Simulation
experiments also show its tolerance to certain level of noise.
