Digital cameras

• Taking a picture on a digital camera

  1. Open shutter

  2. Allow light to enter through lens

  3. Lens focuses light onto image sensor

  4. Image sensor is an array of millions of photosites (light-sensitive elements)

  5. Picture is broken up into millions of pixels
• Photosites


  Measure only the intensity of the light
• Bayer filter


  • Sits above the image sensor
  • Provides an array of red, green, and blue filters, one for each photosite
  • There are twice as many green filters as red and blue filters, to match the colour sensitivity of the human eye
• Determining the colour of each pixel

  1. Bayer filter measures the intensity of red, green, or blue light at each photosite

  2. Final value for each pixel is derived from its own colour intensity and those of its immediate neighbours through the application of a demosaicing algorithm
• Demosaicing algorithms are closely guarded commercial secrets, as they will ultimately determine the quality of the final image
• Camera image processing


  1. Image processing engine carries out the demosaicing stage

  2. Includes an analogue to digital converter that converts the analogue signal into binary form

  3. Colour of each pixel is represented by a numeric code

  4. Digital photograph is effectively an extremely long string of numbers
• Image processing engine


  In some cameras (and in most mobile phone cameras) will automatically compress images to JPEG format
• Compression rate


  Can usually be set by the user, and a higher compression rate will allow more images to be saved on the camera's internal storage
• Image sensor


  • Larger image sensors have more photosensitive points so are able to capture images with greater fidelity
  • There are two different types: CCD (charge-coupled device) and CMOS (complementary metal-oxide semiconductor)
• CCD sensors


  Produce higher-quality images but are more expensive
• CMOS systems


  Use less energy, so are more popular on mobile phones and other devices that use a lot of power
• You can find many arguments in support of each type of sensor