Patent ID: 7122974

Claim:
A light quantity adjusting method, which is used for driving a light emitting device with a drive current at a first level which is generated in accordance with a modulation signal based on an image signal, and driving said light emitting device with a drive current obtained by adding a drive current at a second level to the drive current at the first level for at least one or both of a predetermined time period right after rise of the modulation signal and a predetermined time period right before fall of the modulation signal, said light quantity adjusting method comprising the steps of: storing a resolution ratio between a drive current setting resolution of first set data used to determine the drive current at the first level and a drive current setting resolution of second set data used to determine the drive current at the second level, and light quantity characteristics representing a relationship between the first set data and a light emission quantity of said light emitting device; and adjusting the light emission quantity of said light emitting device, wherein a value in the first set data is obtained through adjustment for a quantity of light so that the light emission quantity of said light emitting device agrees with a first target value, the value is determined as a first set value used to determine the drive current at the first level, a change amount, from the first set value in the first set data, by which the light emission quantity of said light emitting device agrees with a second target value is calculated using the light quantity characteristics, the calculated change amount is converted into a value in the second set data using the resolution ratio, and the converted value is determined as a second set value used to determine the drive current at the second level, thereby carrying out the light quantity adjustment for obtaining the value in the first set data to simultaneously calculate and determine the second set data.