A Chinese text entry system with eye-tracking technique can be used for computer input of Chinese characters. In one example, a device comprises an optical element configured in a fixed position and configured to provide focus settings, an imager die configured to receive image data through the optical element, and an actuator coupled to the imager die and configured to cause a change in a position of the imager die. The whitening transformation term may be determined, for example, by carrying out a Cholesky factorization of a data correlation matrix, which can be obtained from traffic data values for the received signal. Each metric is associated with an expected performance overhead, and the assignment of metrics to an instance is done such that the performance overhead on that instance andor host does not exceed a threshold. Then, by analyzing how the measured densities of all the patches change with changes in code values, the optimum set or sets of the three input code values, that when used together produce a desired set of aim neutral density patches in a single iteration, are determined.