A digital camera captures images using an image sensor, which converts light into electric signals. The image sensor is typically a CCD or CMOS chip containing arrays of light-sensitive photosites. When the shutter button is pressed, light from the photographed scene hits the image sensor, causing each photosite to generate an electric charge proportional to the light intensity. These charges are converted into digital values and stored as pixels in a memory card. The resolution, or clarity, of the captured images depends on the number of pixels in the image sensor. Common image sensors used in digital cameras include CCD and CMOS sensors.

1. Digital Camera
Definition: A Digital Camera is used for record and stores
the images or photo in a digital form. A digital camera is very
use full to capture a image and after that store it in computer
and processing it and print...
Construction:
A digital camera consists of the following basic parts:
• Lenses: It focuses the image, refracting the light rays comes from the object so that they
converge into a coherent image.
• Diaphragm: It determines the amount light enters through the lenses. It measures as f-number,
the greater the f-number the smaller the opening of the diaphragm.
• Shutter: It determines the speed required for the time of exposure.
• Memory Card: Its simply store the image that was captured.
• CCD or Charge Coupled Device: A group of sensors that converts light into corresponding
electric charge and then store data in digital form.
Working Principle
The concept was a lens capturing a picture and saving it via an electric signal to
magnetic tape.
The first digital, portable and light camera was released by
John Strognofe in 1685.
The pictures from a digital camera are already in the digital format which the computer can easily
recognize (0 and 1). The 0’s and 1’s in a digital camera are kept as strings of tiny dots called pixels.
The image sensors used in a digital camera can be either a Charge Coupled Device (CCD) or a
Complementary Metal Oxide Semi-conductor (CMOS).
The image sensor is basically a micro-chip with a width of about 10mm. The chip consists arrays of
sensors, which can convert the light into electrical charges. Though both CMOS and CCD are very
common, CMOS chips are known to be cheaper. But for higher pixel range and costly cameras mostly
CCD technology is used.
A digital camera has lens/lenses which are used to focus the light that is to be projected and created.
This light is made to focus on an image sensor which converts the light signals into electric signals.
The light hits the image sensor as soon as the photographer hits the shutter button. As soon as the
shutter opens the pixels are illuminated by the light in different intensities. Thus an electric signal is
generated. This electric signal is then further broken down to digital data and stored in a memory card.
Pixel resolution of a Digicam
The clarity of the photos taken from a digital camera depends
on the resolution of the camera. This resolution is always
measured in the pixels. A pixel is a point sample of an image

2. which contains three basic color (RGB) components. Pixel per
square inches determines the resolution of the camera, which
indicates the size and quality of image. If the numbers of
pixels are more, the resolution increases, thereby increasing
the picture quality.
Charge Coupled Device
These are a group of sensors that converts light into corresponding electric charge. Sensors are made
of light sensitive diodes called photosites that convert photons into electrons (electric charges). The
amount of photons exposed by these photosites produce proportional amount of charges. CCD also
includes filters that generate digital form of these charges; a series of filter must unpack the image into
discrete values of Red, Green and Blue (RGB).
There are mainly two regions of a CCD filters. They are
1. Photoactive Region
This is used to convert an electrical signal into a digital signal. The photoactive region mainly consists
of a capacitor array. These arrays can be one-dimensional or two-dimensional depending on the type
of device that uses the CCD. If a line scan camera is used, it introduces a one-dimensional capacitor
array. It is called 1D because it captures the image in 1D form, that is, a single slice of the image. 2D
is used mostly in video applications. This device captures the image in 2D form. The photoactive
region is made out of a layer of silicon.
2. Transmission Region
After the image is projected onto the capacitor array, the control circuit comes into action. This circuit
makes the capacitors send the appropriate signal to a shift register. The shift register converts each
signal into a voltage sequence. This is sampled, digitized and then stored in the memory.
With different modes of operation for the CCD, the type of the device will also differ. There are
versions of CCD called frame transfer CCD and also peristaltic CCD.
Applications
▪ Astronomy
CCD’s are used in astronomy because of their high linearity in
outputs. CCD is used in all the astronomical Ultra violet and
infrared applications. They are also highly efficient in quantum
applications.
Application in astronomy also includes a method called drift
scanning. This method is mainly used to follow the motion of
the sky. This is done by converting a fixed telescope into a
tracking telescope with the application of CCD.
▪ Colour Cameras
For the use of CCD in cameras, a much more advanced for
called 3CCD is used commonly. By using 3CCD devices, the

3. colour separation becomes much improved, thus increasing
the quantum efficiency as well. The image resolution of a
camera completely depends on the CCD chip. When the
photons hit the sensor, the sensor counts their number. So,
the brighter the image at a given point on the sensor, the
larger the value that is ready for that pixel.
CMOS(Complimentary Metal-Oxide Semi Conductor)
Active Pixel Sensor (CMOS APS)
Active Pixel Sensor (APS) is an image sensor, made up of an array of pixel sensors. In these pixel
sensors, each pixel sensor consists of a photo detector and an amplifier. Out of these APS, the most
notable is the CMOS Active Pixel Sensor (CMOS APS). CMOS APS has great applications in cameras
and also DSLRs. It is called so as it is manufactured by the CMOS process. This type of image sensor
is very similar to that of a Charge Coupled Device (CCD). They are also called active pixel sensor
imager and also active pixel image sensor.
The CMOS APS uses a photo detector to detect the light and converts it into electrical signal. This
signal is then amplified using several transistors and is then moved using traditional wires.