Image sensors and optical devices

In image sensors that capture color images, why must color filters be placed over the pixels?

  1. ATo increase the number of pixels
  2. BBecause the photodiode itself cannot distinguish the color (wavelength) of light, only its intensity
  3. CTo protect the photodiodes from heat
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Answer: B. Because the photodiode itself cannot distinguish the color (wavelength) of light, only its intensity

A silicon photodiode generates charge from any light with energy above the band gap regardless of color, so it only knows brightness. Placing red, green and blue filters over individual pixels and measuring the intensity of light passing each filter provides color information.

  • A. Filters do not increase the number of pixels.
  • B. Correct. Photodiodes cannot distinguish color.
  • C. Color filters are not there to protect against heat.
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More Image sensors and optical devices questions

  1. Which image sensor is mainly used in current smartphone cameras?
  2. When the light falling on a reverse-biased photodiode becomes stronger, how does the current (photocurrent) change?
  3. Why do images taken in dark places look grainy (with conspicuous noise)?
  4. Which correctly describes the "conversion gain" of a CMOS image sensor?
  5. What is the main advantage of the scheme used in many CMOS image sensors in which each pixel column has its own AD converter for parallel conversion?