We report progress towards information-efficient quantum imaging. We implemented a 4-mode interferometer (Fig.1) which uses both polarization and spatial encoding to image Hadamard-encoded phase arrays. We used this interferometer with a single-photon source to achieve the theoretical goal of Photon Information Efficiency (PIE)= 2 bits per photon (bpp). This demonstration is a particular case of a generalized M-path interferometer which can yield log2M bits of information with a single measurement of a single photon, the photon being placed in the W state 1/√M (|100·· ·0+|010···0+|000···1). We also demonstrated that a heralded single-photon source can attain a higher PIE than coherent or thermal light.