Among other things, one or more image sensors and techniques for forming image sensors are provided. An image sensor comprises a photodiode array configured to detect light. The image sensor comprises an oxide grid comprising a first oxide grid portion and a second oxide grid portion. A metal grid is formed between the first oxide grid portion and the second oxide grid portion. The oxide grid and the metal grid define a filler grid. The filler grid comprises a filler grid portion, such as a color filter, that allows light to propagate through the filler grid portion to an underlying photodiode. The oxide grid and the metal grid confine or channel the light within the filler grid portion. The oxide grid and the metal grid are formed such that the filler grid provides a relatively shorter propagation path for the light, which improves light detection performance of the image sensor.