Comparison of objective metrics for image sensor crosstalk characterization

Image sensor crosstalk can be divided into spectral crosstalk and pixel crosstalk. This paper focuses on the pixel crosstalk and its effect on signal to noise ratio (SNR). Pixel crosstalk occurs in the spatial domain and is due to the signal leakage between adjacent pixels either by imperfect optical isolation or diffusion of electrons. This will have a negative impact on image quality mainly in two ways: spatial blurring and decreased SNR due to more aggressive color correction required. A method for modeling the spectral broadening due to the pixel crosstalk is used where a matrix is calculated from crosstalk kernels representing the spatial leakage between neighboring pixels. In order to quantify the amount of crosstalk we present a method in which ratios of integrals of the same color channel but within different wavelength intervals are calculated. This provides a metric that is more robust with respect to color channel scaling. To study the impact on SNR due to pixel crosstalk, a number of SNR metrics are compared to results from a limited psychophysical study. The studied SNR metrics are the metric used for calculating the SNR10 value in mobile imaging, the ISO 12232 noise metric and a metric where the signal is transformed into orthogonal color opponent channels, thereby enabling the analysis of the luminance noise separate from the chrominance noises. The results indicate that the ISO total noise and SNR10 metric yield very similar results and that the green channel has the largest individual impact on the crosstalk.