The following methods are conventionally used to control or determine a light emission amount when an image is sensed by using a flash of an image sensing apparatus.
First method: Flash light is emitted toward an object to receive the reflected light from the object by a sensor. When the obtained integral value has reached a defined value, the light emission is stopped.
Second method: Preemission is performed once, and the brightness of an object at that time is loaded by an image sensor. On the basis of this loaded condition, the light amount for image sensing is determined.
Third method: Preemission is repeated a number of times, and the light emission amount for image sensing is determined by integrating the brightness.
In the first method, however, the sensor for receiving the reflected light from an object is necessary in addition to the image sensor. This is disadvantageous in making the image sensing apparatus compact and reducing the cost. Also, no correct light amount can be obtained by the sensor depending on the reflectance or position of an object.
In the second method, no correct light amount can be determined unless the object's brightness indicated by the reflected light obtained by preemission is appropriate (not too bright or not too dark).
To solve these problems, the light amount of preemission can be selected on the basis of distance information. However, the determined light amount for image sensing can be inappropriate in some cases owing to calculation errors of the distance information. Also, this method cannot be performed if a distance information collecting means such as auto-focusing is omitted in order to make the image sensing apparatus compact or reduce the cost.
In the third method, electricity and time are wasted by a number of times of preemission. Time is wasted especially when a light emitting device (e.g., a light emitting device using an LED as a light emitting means) which emits weak light and requires a long irradiation time is used.
The present invention relates to a light emitting device for an image sensing apparatus, an image sensing apparatus with a light emitting device, and an image sensing method which have been made to solve the above conventional problems.