By-her W. Richards

Evaluation of LED flash performance for camera phones

In this work, LED based flash solutions are evaluated for use in a camera phone application. The performance of a given flash solution is measured in terms of color accuracy and signal to noise ratio (SNR), both of which are standard test methods used in industry. Early in a camera phone design before completed camera modules are available, color accuracy and SNR are evaluated through a model which is based on knowledge of a given image sensors color response as well as the power spectral distribution of the flash. Later in the design, when working camera modules become available, the evaluation is performed through direct measurement. These direct measurements are also used to verify the results of the aforementioned model. Color accuracy, SNR, how they are related, and the compromise between the two are discussed as well as the efficiency at which electrical power is converted to light that is detectable by the image sensor. Though many issues remain to be investigated, measuring color accuracy and SNR provides an evaluation method that builds on developed techniques and provides a practical foundation for flash evaluation as it applies to the camera phone industry.