An array of sensor pixels is formed on a substrate, and a signal processing unit is connected to the array of sensor pixels. The signal processing unit includes multiple spectral channels that are defined by a respective transmission curve of each optical filter of at least one associated sensor pixel. Each of the sensor pixels includes a stack of a respective photodetector and a respective optical filter. Each spectral channel receives an output signal from one or more sensor pixels including an optical filter having the same transmission curve. At least one spectral channel has a greater number of sensor pixels than another spectral channel among the multiple spectral channels. The different number of pixels for the spectral channels can be employed to compensate for variations of sensor efficiency as a function of wavelength. Adjustment to sensor gain can be minimized through use of different number of pixels for different spectral channels.