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The colour gamut, a two-dimensional (2D) colour space primarily comprising hue and saturation (HS), lays the most important foundation for the colour display and printing industries. Recently, the metasurface has been considered a promising paradigm for nanoprinting and holographic imaging, demonstrating a subwavelength image resolution, a flat profile, high durability, and multi-functionalities. Much effort has been devoted to broaden the 2D HS plane, also known as the CIE map. However, the brightness (B), as the carrier of chiaroscuro information, has long been neglected in metasurface-based nanoprinting or holograms due to the challenge in realising arbitrary and simultaneous control of full-colour HSB tuning in a passive device. Here, we report a dielectric metasurface made of crystal silicon nanoblocks, which achieves not only tailorable coverage of the primary colours red, green and blue (RGB) but also intensity control of the individual colours. The colour gamut is hence extruded from the 2D CIE to a complete 3D HSB space. Moreover, thanks to the independent control of the RGB intensity and phase, we further show that a single-layer silicon metasurface could simultaneously exhibit arbitrary HSB colour nanoprinting and a full-colour hologram image. Our findings open up possibilities for high-resolution and high-fidelity optical security devices as well as advanced cryptographic approaches.

Printing image based on metasurface has attracted enormous research interests due to its subwavelength resolution, full‐color printing, and durable properties. Based on the spatially multiplexed pixels, the printing image using metasurface can be switched optically by altering the optical parameters, such as polarization and incident wavelength. However, such multiplexed pixel design has several problems, including the cross‐talk among different wavelengths, limitation to linear polarizations, and incapability for incident‐angle control. Here, a general method for pixel design, called the coherent pixel, which can overcome the problems and be used for multiple printing‐image switching controlled by arbitrary optical parameters (arbitrary incident angle, polarization, and wavelength) is proposed. Based on this coherent pixel, metasurface devices with novel functionalities can be realized, such as incident‐angle controlled and arbitrary polarization‐controlled printing images, which are not feasible with previous conventional pixel design method. The suitability and superiority of the coherent pixel for encryption application is also discussed. Such printing‐image switching controlled with arbitrary optical parameters should pave the way for various applications, including various functional switchable optical devices, image displays, and information encryption.

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