Abstract: A method of controlling exposure of a medium comprises the step of changing an emission level of a radiation source from a first power to a second power. The second power emits for less time than required by an irradiance profile to traverse a full-width at half maximum of the irradiance profile projected onto the medium along a direction of relative motion between the irradiance profile and the medium. The emission level changes to the first power and emits for less time than required by the irradiance profile to traverse the full-width at half maximum of the irradiance profile projected onto the medium along the direction of relative motion between the irradiance profile and the medium, then the emission level changes to the second power. Brief pulsing of a single binary source can transfer intermediate amounts of thermally transferable colorant from a donor exhibiting a continuous-tone transfer response.