CHAPTER-01 : 1.1 DIGITAL IMAGE PROCESSING

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Image Editing / Digital Imaging

"Manipulating of digital images using an existing software application such as ADOBE PHOTOSHOP , CORAL PAINT and etc."


Digital Image Processing
"The conception,design,development and enhancement of digital imaging programs."

Computer Graphics
"Graphics created using computer and the representation of image data by a computer from geometrical descriptions."




Pin-Hole Camera Model
Focal Length : The distance between the lens and sensor in optical devices
 - The system with the shorter focal length has greater optical power than one with the long focal length.
Exposure Time /Shutter Time : A length of time camera's shutter is open when taking a photograph.
 - The camera's shutter speed, the lens brightness and scene luminance together determine the amount of light that reaches the film or amount of light that reaches the film or sensor.
There are some example images are below,

An extended exposure can also allow photographers to catch brief flashes of light, as seen here. Exposure time 15 seconds.

Shutter speed can have a dramatic impact on the appearance of moving objects. Changes in background blurring are apparent as exposure time increases.



Slow shutter speed combined with panning the camera can achieve a motion blur for moving objects.

The photograph to the right was taken with a slower shutter speed than that to the left, creating a more pronounced motion blur effect and longer streaks of light from vehicle headlights.

Going Digital

What is projected on the image plane of our camera is essentially a 2D. time-dependent,continuous distribution of light energy. In order to obtain a "Digital Snapshot" of the continuously changing light distribution for processing it our computer.Three main steps necessary for Digitizing an image.

 1. Spatial Sampling : is depends on the sensor device's geometrical plane.
    - An individual sensor's are usually designed as by rectangular array on the sensor plane.
    -Other types of arrangement are hexagonal, circular, pentagon and etc.
 
2. Temporal Sampling : is measuring at regular interval how much amount of light received on each  individual sensor element in a particular exposure time.
  - CCD (Charged Coupled Device) / CMOS(Complementary Metal Oxide Semi conductor) do this
    job (Electrical Charging) on Digital Camera.

CCD from a 2.1 megapixel Argus digital camera

 
A Bayer filter on a CCD

x80 microscope view of an RGGB Bayer filter on a 240 line Sony CCD PAL Camcorder CCD sensor

3.Quantization of pixel values : In order to store and process the image values on the computer they are commonly converted to a  range of numerical values ( example 0......255 for 8 bits )  
This process is carried out by analog to digital converters which are either embedded with the sensor electronics or special interface hardware. 




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