The signal from detected photons is ultimately stored in capacitors prior to readout.

• A. Capacitors
• B. Diodes
• C. Transistors
• D. Resistors

Answer: (A)

The signal from detected photons is stored as electric charge on capacitive storage in each pixel. When photons hit the photosensitive surface, they generate charge that accumulates in a small capacitance within the pixel (a potential well). This stored charge is proportional to the light intensity and remains there until the readout stage, where it is converted into a voltage for digitization. In imaging detectors such as CCDs and CMOS sensors, this storage element is the capacitor-like node that holds the charge before it’s processed. Other components, like diodes, transistors, or resistors, play roles in converting light to charge, switching or biasing, or shaping the signal, but the actual hold-forever-before-readout function is performed by the storage capacitor.