Image capturing device and brightness adjusting method

A brightness adjusting method applied to an image capturing device, the image capturing device comprising a plurality of light emitters, an image capturer, a memory and a processor, the memory storing a target brightness value, the processor being electrically connected the light emitters, the image capturer and the memory, the brightness adjusting method comprising steps of:

• the processor controlling the light emitters to emit light;
• the processor controlling the image capturer to capture an image, wherein the image is divided into a plurality of areas and the light emitted by each of the light emitters corresponds to one of the areas;
• the processor calculating a current brightness value of each area and calculating an absolute difference between the current brightness value of each area and the target brightness value;
• the processor determining whether each absolute difference is larger than a first threshold;
• according to a determination result, the processor calculating an amount M of the areas with the current brightness value larger than the target brightness value and calculating another amount N of the areas with the current brightness value smaller than the target brightness value, wherein M and N are equal to 0 or an positive integer, and M and N are not equal to 0 simultaneously;
• the processor determining whether M or N is larger than a second threshold;
• when M or N is larger than the second threshold, the processor adjusting an exposure parameter of the image capturer;
• and
• when M and N both are not larger than the second threshold, the processor adjusting a light emitting intensity of the light emitter corresponding to the area with the absolute difference larger than the first threshold.