Image Representation

We have seen that the human visual system (HVS) receives an input
image as a collection of spatially distributed light energy; this is form is
called an optical image. Optical images are the type we deal with every
day –cameras captures them, monitors display them, and we see them
[we know that these optical images are represented as video information
in the form of analog electrical signals and have seen how these are
sampled to generate the digital image I(r , c).
The digital image I (r, c) is represented as a two- dimensional array of
data, where each pixel value corresponds to the brightness of the image at
the point (r, c). in linear algebra terms , a two-dimensional array like our
image model I( r, c ) is referred to as a matrix , and one row ( or column)
is called a vector.
The image types we will consider are:

1. Binary Images
Binary images are the simplest type of images and can take on two
values, typically black and white, or ‘0’ and ‘1’. A binary image is referred to as a 1 bit/pixel image because it takes only 1 binary digit to
represent each pixel.
These types of images are most frequently in computer vision application
where the only information required for the task is general shapes, or
outlines information. For example, to position a robotics gripper to grasp
an object or in optical character recognition (OCR).
Binary images are often created from gray-scale images via a threshold
value is turned white (‘1’), and those below it are turned black (‘0’).
We define the characteristic function of an object in an image to be


(a) (b)

Figure(1) (a) binary image representation (b) binary Lenna image
• Each pixel is stored as a single bit (0 or 1)
• A 640 x 480 monochrome image requires 37.5 KB of storage.

2-Gray Scale Images
Gray _scale images are referred to as monochrome, or one-color image.
They contain brightness information only brightness information only, no
color information. The number of different brightness level available.
The typical image contains 8 bit/ pixel (data, which allows us to have (0-255) different brightness (gray) levels. The 8 bit representation is
typically due to the fact that the byte, which corresponds to 8-bit of data,