2. Digital rather than film
• Rather than using a film, the digital still camera
contains a sensor which converts light into electrical
charges.
• The sensor is either a charge coupled device (CCD)
or complementary metal oxide semiconductor
(CMOS) technology.
• The sensor changes the light to electrons, which
then means it can read the accumulated charge of
each cell in the image.
3. CCDs
• A CCD moves the charge across the chip so it can
read it a corner of the array.
• Something called an analogue-to-digital
converter (ADC) turns each pixel’s value into a
digital value
• It does this by measuring the amount of charge at
each photosite and converting it into binary form
• The advantage of CCDs mean that high-quality
images are produced. However, they consume
100 times as much power as a CMOS sensor
4. CMOS
• A CMOS device uses transistors at each pixel
to amplify and move the charge using wires.
• The advantage of a CMOS sensor is that it
consumes less power although they are much
more susceptible to noise.
5. Capturing Colour
• As each photosite is colourblind, the sensors
have to use filters to look at the light in the
primary colours of light. This allows the
camera to create a full spectrum.
6. Capturing Colour – Beam Splitter
• One way of recording the three colours in a DSC is to use a
beam splitter.
• This directs the light to different sensors
• Each sensor sees the same image, but due to the filter, each
sensor only responds to its appropriate colour.
• The advantage of this is that the camera can record each
colour at each pixel location
7. Capturing Colour - Rotation
• Another method is to rotate red, blue and
green filters in front of one sensor
• The sensor records three different images in
succession.
• This allows the information of the three
colours to be recorded at each pixel location
• Unfortunately, as the images aren’t taken at
the same time, the camera and target must
stay stationary for the three readings.
8. Capturing Colour - Filtering
• A cheaper method to record the primary colours is by placing
a permanent filter called a ‘colour filter array’ over each
photosite.
• This means information around each sensor can guess what
the true colour is at the location. This is called ‘interpolation’
• The most common filter pattern is the Bayer filter pattern.
• The advantage of this is that only one sensor is needed, and
that all colours are recorded in the same moments.
9. Taking a Photo – CCD
• After lightly pressing the shutter release, the camera
focuses on the subject and takes a reading of the existing
light
• The camera sets the aperture and shutter speed for the
best exposure
• After pressing the shutter release down all the way, the
camera resets the CCD and exposes it to the light, which
builds up an electrical charge until the shutter closes.
• The ADC measures the charge and creates a digital signal
• The process interpolates the data to cerate natural colour.
You can now see the output on the LCD screen.
10. Storing the Photos
• To make the most of the storage space in removable storage
devices (SD Cards) used in digital cameras, is by using a form
of data compression which makes the files smaller.
• Two features of digital images make this possible; repetition
and irrelevancy.
• In a photo, patterns develop in the colours. The compression
takes advantage of these repeating patterns so that there is
no loss of information, Unfortunately, only up to 50% is
reduced.
• When the camera takes the picture, more information is
recorded than the human can detect. This means that this
information can be thrown away during the compression
routine.
