Among other things, one or more image sensors and techniques for guiding light towards a photodiode are provided. An image sensor comprises a metal grid configured to direct light towards a corresponding photodiode and away from other photodiodes. The image sensor also comprises a dielectric grid and a filler grid over the metal grid to direct light towards the corresponding photodiode and away from other photodiodes, where the filler grid has a different refractive index than the dielectric grid. In this way, crosstalk, otherwise resulting from detection of light by incorrect photodiodes, is mitigated.