LED array with graduated quantity control

Claim 1

In a method for forming an image on a light-sensitive material by controlling a quantity of light received on a light-sensitive material by gradation-controlling a light-emitting diode array, the improvement comprising: establishing light-emitting intensities of diodes constituting said light-emitting diode array at a constant level, and controlling a quantity of light received on said light-sensitive material in a predetermined period by changing light-emitting periods of time of the respective light-emitting diodes correspondingly to recording gradation data, in which the light-emitting diode array is composed of a plurality of light-emitting diodes which are N in number, and in which an image having 2 k gradations is recorded on said light-sensitive material by provision of: an m-stage ring counter for counting pulses of a first clock signal of a predetermined frequency to divide a period T for deriving each of the N light-emitting diodes by 2 k ; an N-stage ring counter for counting pulses of a second clock signal of a predetermined frequency; a line memory of N×k bits receiving an output of the N-stage ring counter as an address signal; a comparator for comparing image data produced by said line memory with an output of said m-stage ring counter to thereby produce binary-coded data; a shift register of N bits receiving the binary-coded data in synchronism with said second clock signal; and a driving circuit for transferring in parallel an output of said N-bit shift register to said light-emitting diodes to drive the latter.