In this paper we formulate the basic concept of a bichromatic image technique. Specific examples of its application are analyzed in the context of research into solar plasma characteristics by pinpointing its merits and demerits. Specialized requirements to the spectral devices are set forth, which may be summarized as: a) the presence of two nearby identical spectral passbands; b) the mutual orthogonality for the polarization of the light that has passed through neighboring bands; and c) the

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... ssibility of controlling the relative position of the bands. Several alternative plausible implementations of the method are considered with the use of Fabry-Perot interferometers (FPI) and magnetooptical filters (MOF) for measuring the longitudinal magnetic field strength and the intensity field. A new design of a filter magnetograph is proposed, based on MOF, with the combination of two optical resonance cells into one.