Image Processing

Digital Image Processing

Chapter 2: Digital Image Fundamentals

Elements of Visual Perception

Structure of the human eye

Rods and cones in the retina

Image formation in the eye

Brightness adaptation and discrimination

Brightness discrimination

Weber ratio

Perceived brightness

Simultaneous contrast

Optical illusion

Light and the Electromagnetic Spectrum

Wavelength

c

hE

Image Sensing and Acquisition

Image acquisition using a single sensor

Using sensor strips

A simple image formation model

Illumination and reflectance Illumination and transmissivity

),(),(),( yxryxiyxf

Image Sampling and Quantization

Sampling and quantization

Representing digital images

Number of storage bits

Spatial and gray-level resolution

Subsampled and resampled

Varying the number of gray levels

Varying the number of gray levels

N and k in different-details images

Isopreference

Moire pattern

Zooming and shrinking

Some Basic Relationships Between Pixels

Neighbors of a pixel : 4-neighbors of p

, , ,

: four diagonal neighbors of p , , ,

: 8-neighbors of p and

)(4 pN

),1( yx )1,( yx),1( yx )1,( yx

)1,1( yx )1,1( yx)1,1( yx

)1,1( yx

)( pND

)(8 pN)(4 pN )( pND

Adjacency : The set of gray-level values used to

define adjacency 4-adjacency: Two pixels p and q with

values from V are 4-adjacency if q is in the set

8-adjacency: Two pixels p and q with values from V are 8-adjacency if q is in the set

V

)(4 pN

)(8 pN

m-adjacency (mixed adjacency): Two pixels p and q with values from V are m-adjacency if

q is in , or q is in and the set has

no pixels whose values are from V

)(4 pN)( pND )()( 44 qNpN

Subset adjacency S1 and S2 are adjacent if some pixel in

S1 is adjacent to some pixel in S2 Path

A path from p with coordinates to pixel q with coordinates is a sequence of distinct pixels with coordinates

, ,…, where = , = ,

and pixels and are adjacent

),( yx),( ts

),( 00 yx ),( 11 yx ),( nn yx),( 00 yx ),( yx ),( nn yx ),( ts

),( ii yx ),( 11 ii yx

Region We call R a region of the image if R is a

connected set Boundary

The boundary of a region R is the set of pixels in the region that have one or more neighbors that are not in R

Edge Pixels with derivative values that

exceed a preset threshold

Distance measures Euclidean distance

City-block distance

Chessboard distance

2

122 ])()[(),( tysxqpDe

|)(||)(|),(4 tysxqpD

|))(||,)(max(|),(8 tysxqpD

mD distance: The shortest m-path between the points

Linear operation H is said to be a linear operator if, for

any two images f and g and any two scalars a and b,

)()()( gbHfaHbgafH

Example

Zooming and Shrinking Images by Pixel Replication

(a) Write a computer program capable of zooming and shrinking an image by pixel replication. Assume that the desired zoom/shrink factors are integers. You may ignore aliasing effects. You will need to download Fig. 2.19(a).

(b) Download Fig. 2.19 (a) and use your program to shrink the image from 1024 x 1024 to 256 x 256 pixels.

(c) Use your program to zoom the image in (b) back to 1024 x 1024. Explain the reasons for their differences.

http://home.kimo.com.tw/abc9250/BMP_FILE.htm

Fig2.19(a).bmp subsample.c resample.c