Abstract: An active optical machine-readable tag that is addressable and readable within a line-of-sight of a reader device equipped with a camera, at substantially large distances. The active optical tag and the camera-based reader may use a method of asynchronous communication reducing the flicker associated with the low-frequency optical carrier to a level hardly noticeable by people. The method of transmitting data may include determining length of a repetitive time period not longer than time resolution of a human eye, emitting a first sequence of light pulses within the time period, the light pulses including pulses of complementary colors and pulses of different levels of luminosity; and determining the order of the colors and levels of luminosity of the first sequence of light pulses emitted within the time period to represent a symbol, and to achieve perceived chromaticity and luminosity that is substantially constant to a human eye.

Abstract: An active optical machine-readable tag that is addressable and readable within a line-of-sight of a reader device equipped with a camera, at substantially large distances. The active optical tag and the camera-based reader may use a method of asynchronous communication reducing the flicker associated with the low-frequency optical carrier to a level hardly noticeable by people. The method of transmitting data may include determining length of a repetitive time period not longer than time resolution of a human eye, emitting a first sequence of light pulses within the time period, the light pulses including pulses of complementary colors and pulses of different levels of luminosity; and determining the order of the colors and levels of luminosity of the first sequence of light pulses emitted within the time period to represent a symbol, and to achieve perceived chromaticity and luminosity that is substantially constant to a human eye.