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Image sensor question (very basic)

  1. Jan 20, 2013 #1
    I understand the role of an image sensor is to convert incoming light into electrical charge (by splitting the light into RGB values and then measuring the intensities of each), but how does this occur?

    I know the answer is very basic (the sort of sensors I'm talking about are CCDs and CMOS). Am I correct in thinking that the incoming light strikes the material, excites some of the electrons into the conduction band which then makes them free to travel in the material and this charge is measured?

    Any help would be appreciated! Thanks
  2. jcsd
  3. Jan 20, 2013 #2


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    Just to cover basics, you should look up 'Image sensor', 'Charge-coupled device', and 'Active pixel sensor' at Wikipedia.

    The most common way of 'splitting' up colour is actually to only have separate red, green, and blue sensors placed in very close proximity (with enough spectral 'overlap' so as to be able to detect in-between values such as yellow). Incidentally, this is how the red, green, and blue photoreceptors in our own eyes work.

    As to the how of the sensors, CCD are different from CMOS sensors. CCDs have photosensitive regions operating basically on the principle you describe, with the excited charge accumulating in these sensor regions (acting as capacitors, which can then be read). CMOS sensors are based on photodiodes or phototransistors, conducting only when there's enough incident light, with more photons causing more conduction.
  4. Jan 21, 2013 #3


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    The RG and B signals that come from the colour processing in the camera are not the values that the sensor produces. RG&B signals (a 'vector' with three coordinates) are obtained by multiplying the three sensor outputs (another vector) by a (3X3) matrix. This is a fact that nearly everyone ignores. RGB values are what is supplied to the Display. Proper colour reproduction would not work if it weren't done this way. This is one reason that colour film gives such poor (inaccurate but, sometimes, nice to look at) colour quality. It's along the same lines as Vinyl and Tape analogue recording - poor but pleasant.
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