Improvement of imaging quality with a donut-shaped LED fill light for smartphone flashlight

In this study, a wide-angle auxiliary fill lamp (WAFL) intended to assist the built-in flashlight of smartphone cameras had been proposed in simulations and measurements. The WAFL generates a donut-shaped light pattern that perfectly combines with the light pattern produced by a pre-improved smartphone flashlight (SF). The improved SF provides a broader and more uniform light energy distribution, so as to effectively solve the problem of insufficient SF illumination range. In addition, an image processing method which uses the known illumination distribution of the SF to simply calibrate the luminance of the image and enhance its uniformity, is also proposed in this study. According to the experimental results, uniformity and the signal-to-noise ratio of an image taken with a camera using the improved SF are better than those taken with a camera using only the SF.