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DIGITAL IMAGE PROCESSING - · Digital Image Processing The field of digital image processing refers to processing digital images by using computers. Image processing

Nov 03, 2019






    Asstt. Prof., ECE department.

    MMEC, MM University, Mullana.

  • Why Image Processing?

    For Human Perception

    To make images more beautiful or understandable

    Automatic Perception of Image

    We call it Machine Vision, Computer Vision, Machine

    Perception, Computer Recognition

    For Storage and Transmission

    smaller, faster, more effective

    Image Processing for New Image Generation (New trends)

    Computer Graphics introduced Image Processing and

    Computer Vision technologies

    ECE-411 (Image Processing)

  • The Electromagnetic Spectrum

    Images based on radiation from the EM spectrum

    EM : wave stream of mass less particles

    Each particle contains energy

    ECE-411 (Image Processing)

  • Example: a cell

    Image of a cell corrupted by

    electronic noise.

    Result after averaging

    several noisy images (a

    common technique for noise


    ECE-411 (Image Processing)

  • Example: an x-ray

    An original x-ray image

    Result possible after

    contrast and edge


    ECE-411 (Image Processing)

  • Example: image deblurring

    Image of a human face

    blurred by uniform motion

    during exposure.

    Resulting image after

    application of a deblurring


    ECE-411 (Image Processing)

  • Simple Image Model

    Monochrome image (or simply image) refers to a 2-

    dimensional light intensity function f(x,y).

    x and y denote spatial coordinates

    the value of f(x,y) at (x,y) is proportional to the brightness (or gray

    level) of the image at that point.

    ECE-411 (Image Processing)

  • Simple image formation

    f(x,y) = i(x,y)*r(x,y) 0 < i(x,y) < ∞ ; illumination or intensity of incident light

    0 < r(x,y) < 1 ; reflectance or reflectivity of object.

    In real situation

    Lmin ≤ f(x,y)) ≤ Lmax

    ECE-411 (Image Processing)

  • Why Digital? Unification of processing

    Computers is at the center of information processing

    Digital information is just right form for computer


    Text, Image, Sound, Movie, and other Multimedia are

    digitized into computer

    Noise reduction

    Digital processing reduces noises

    Guarantee the same quality regardless of time and place

    Easy storage

    Since the same form is used for every information, it can be

    stored in H/D, CD, DVD, Flash memory, etc.


    Less Bandwidth ECE-411 (Image Processing)

  • Digital image

    A digital image is an image f(x,y) that has been discretized

    both in spatial coordinates and in brightness.

    Considered as a matrix whose row and column indices

    represent a point in the image.

    The corresponding matrix element value represents the gray

    level at that point.

    The elements of such an array are referred to as:

    image elements or picture elements (pixels or pels)

    ECE-411 (Image Processing)

  • ECE-411 (Image Processing)

  • Digital Image Processing

    The field of digital image processing refers to processing

    digital images by using computers.

    Image processing is a branch in which both the input and

    output of a process are images.

    The goal of computer vision is to use computers to emulate human vision, including learning, making inferences and taking actions.

    The area of image analysis is in between image processing and computer vision.

    ECE-411 (Image Processing)

  • Types of Processes in Image Processing

    There are 3 types of computerized processes. Low level processes mid level processes and high level processes.

    Low-level processes involve primitive operations such as image preprocessing to reduce noise, contrast enhancement and image sharpening.

    Here both the input and output are images.

    Mid-level processing involves segmentation (partitioning image into regions), description of objects to reduce them to a form so that a computer can process and classification (recognition) of objects.

    Here inputs are images but outputs are attributes extracted from images.

    ECE-411 (Image Processing)

  • In high-level processing, we ‘make sense’ of a collectionof recognized objects.

    The process of acquiring an image of a text, processing it,extracting (segmenting) individual characters, describingcharacters suitable for computer processing andrecognizing those individual characters are in the scope ofdigital image processing.

    Making sense of the content of the page (text) is viewedas the domain of image analysis and computer vision.

    ECE-411 (Image Processing)

  • Fundamental steps in Digital Image


    Image acquisition

    Image enhancement

    Image Restoration

    Color Image Processing

    Image Compression

    Morphological Processing

    Image Segmentation

    Representation and description


    ECE-411 (Image Processing)

  • Fundamental steps in Digital Image


    ECE-411 (Image Processing)

  • Steps in an image processing system

    Image acquisition

    This stage involves preprocessing, such as scaling.

    Acquire a digital image using an image sensor

    In detail, devices that are sensitive to

    energy(electromagnetic, sound, … )

    If not digital, an analog-to-digital conversion process is


    The nature of the image sensor (and the produced image)

    are determined by the application

    In general, CCD(charge-coupled device) or CMOS sensors

    are widely used

    Examples : Digital camera, Video camera, Scanner, ..ECE-411 (Image Processing)

  • CCD (Charged-Coupled Device) cameras

    Tiny solid state cells convert light energy into electrical


    The image plane acts as a digital memory that can be read

    row by row by a computer.

    ECE-411 (Image Processing)

  • Steps in an image processing system

    Image enhancement – Here we bring out details that were obscured or highlight some features of interest in an image. (eg) increasing the contrast of an image.

    Image Restoration – Here we talk about how to improve the appearance of an image. Unlike enhancement, which is subjective, this is objective.

    Color Image Processing – Due to Internet, this area is becoming popular. Various color models are worthy to know.

    Wavelets – Representing the images in various degrees of resolution in the basis of wavelets.

    ECE-411 (Image Processing)

  • Steps in an image processing system

    Compression – It is a technique for reducing the storage required to save an image or bandwidth needed to transmit.

    Morphological Processing – It deals with tools for extracting image components that are useful in the representation and description of shape.

    ECE-411 (Image Processing)

  • Steps in an image processing system


    Broadly defined: breaking an image into its constituent parts

    In general, one of the most difficult tasks in image processing

    Good segmentation simplifies the rest of the problem

    Poor segmentation make the task impossible

    Output is usually raw pixel data: may represent region boundaries,

    points in the region itself, etc.

    Boundary representation can be useful when the focus is on external

    shape characteristics (e.g. corners, rounded edges, etc.)

    Region representation is appropriate when the focus is on internal


    ECE-411 (Image Processing)

  • Steps in an image processing system

    Representation & description

    Representation: transforming raw data into a form suitable

    for computer processing

    Description (also called feature extraction) deals with

    extracting features that result in some quantitative

    information of interest or features which are basic for

    differentiating one class of objects from another

    In terms of character recognition, descriptors such as lakes

    (holes) and bays help differentiate one part of the alphabet

    from another

    ECE-411 (Image Processing)

  • Steps in an image processing system

    Recognition & Interpretation

    Recognition: The process which assigns a label to an object

    based on the information provided by its descriptors

    may be the alphanumeric character A

    Interpretation: Assigning meaning to an ensemble of

    recognized objects.

    35487-0286 may be a ZIP code

    ECE-411 (Image Processing)

  • The knowledge base

    • Knowledge about a problem domain is coded into an image

    processing system in the form of a knowledge database

    May be simple:

    detailing areas of an image expected to be of interest

    May be complex

    A list of all possible defects of a material in a vision

    inspection system

    Guides operation of each processing module

    Controls interaction between modules

    Provides feedback through the system

    ECE-411 (Image Processing)

  • Steps in an image processing system

    Not all image processing systems would require all

    steps/processing modules

    Image enhancement for human visual perception may not

    go beyond the preprocessing stage

    A knowledge database may not be required

    Processing systems which include recognition and

    interpretation are associated with image analysis systems in

    which the objective is autonomous (or at least partially


    ECE-411 (Image Processing)

  • Components of an Image Processing


    ECE-411 (Image Processing)

  • Basic components of a general-purpose

    system used for digital image processing Image sensors – Two elements are needed to acquire digital


    First one is the physical device that is sensitive to energyradiated by the object that we want to image.

    The second one, called the digitizer, is a device forconverting the output of the physical sensing device intodigital form.

    Ex. - in a digital video camera, the sensors produce anelectrical output proportional to light intensity.

    ECE-411 (Image Processing)

  • Basic components of a general-purpose

    system used for digital image processing

    Specialized Image Processing Hardware -

    It consists of digitizer plus hardware that performs other primitive operations such as an arithmetic logic unit (ALU), which performs arithmetic and logical operations on entire image.

    This type of hardware is also called as front-end subsystem and its characteristic is speed.

    This unit does things that require fast data throughputs which main computer cannot handle.

    Computer – In an image processing system it is a general-purpose computer.

    Software – It consists of specialized modules that does specific tasks (eg. matlab)

    ECE-411 (Image Processing)

  • Basic components of a general-purpose system

    used for digital image processing

    Mass storage – An image of 1024 X 1024 size, storing theintensity of each pixel in 8 bits, requires one megabyte ofstorage.

    For short-time storage, we can use computer memory.

    Another method is to use a specialized board called framebuffer, that store one or more images and can be accessedrapidly.

    They enable us to instantaneously zoom, scroll (verticalshift) and pan (horizontal shift).

    For on-line storage magnetic disks or optical-media areused.

    The archival storage needs massive capacity but areaccessed infrequently.

    Image Displays – These are mainly color TV monitors.

    Hardcopy – These devices include laser printers, filmcameras, inkjet units, etc.

    ECE-411 (Image Processing)

  • Sampling & Quantization

    Image sampling

    Digitization of spatial coordinates (x,y)


    Amplitude digitization

    The quality of a digital image is determined to a large degree

    by the number of samples and discrete gray levels used in

    sampling and quantization

    ECE-411 (Image Processing)

  • Sampling & Quantization

    ECE-411 (Image Processing)

  • ECE-411 (Image Processing)

  • The intensity variation sampled at regular

    intervals along the scan line

    0 10 20 30 40 50 60 70 80 90 10050






    ECE-411 (Image Processing)

  • Four level intensity quantization of

    sampled scan line

    0 10 20 30 40 50 60 70 80 90 10060











    ECE-411 (Image Processing)

  • Formulation of Digital Image

    ECE-411 (Image Processing)

  • ECE-411 (Image Processing)

  • Image Resolution

    Spatial Resolution (x,y)

    Spatial resolution is the smallest discernible detail in an image

    A line pair : a line and its adjacent space

    A widely used definition of resolution is the smallest number of discernible line pairs per unit distance .

    Ex: 100 line pairs/mm

    But, unit distance or unit area is omitted in most cases

    ECE-411 (Image Processing)

  • Spatial Resolution

    ECE-411 (Image Processing)

  • Image Resolution(Cont..)

    Gray-level Resolution

    Gray-level resolution is the smallest discernible change in

    gray level (but, highly subjective!)

    Due to hardware considerations, we only consider

    quantization level

    Usually an integer power of 2. The most common level is


    However, we can find some systems that can digitize the

    gray levels of an image with 10 to 12 bits of accuracy.

    ECE-411 (Image Processing)

  • Gray-level Resolution

    ECE-411 (Image Processing)

  • Storage

    For MxN image with L(=2k) discrete gray level The number, b, of bits required to store the image is

    b = M*N*k bits

    Ex1: 1024x1024x8bit = 1Mbytes

    Common image file formats GIF (Graphic Interchange Format) -

    PNG (Portable Network Graphics)

    JPEG (Joint Photographic Experts Group)

    TIFF (Tagged Image File Format)

    PGM (Portable Gray Map)

    FITS (Flexible Image Transport System)

    ECE-411 (Image Processing)

  • Overview of MATLAB Data Types

    Data Types

    Logical (0 or 1)

    Char Numeric


    Signed Unsigned


    Single Double

    Function handling

    StructureCell or Array

  • Overview of MATLAB Data Types

    Data types in MATLAB

    Double (64-bit double-precision floating point)

    Single (32-bit single-precision floating point)

    Int32 (32-bit signed integer)

    Int16 (16-bit signed integer)

    Int8 (8-bit signed integer)

    Uint32 (32-bit unsigned integer)

    Uint16 (16-bit unsigned integer)

    Uint8 (8-bit unsigned integer)

  • Image types

    x(m,n) = 0 or 1: binary image

    x(m,n) = 0, 1, 2, … P-1: grayscale image

    P typically something like 256, 512 or some power of 2.

    256 is really the most common

    0 = black, P = white

    x(m,n) = [0 to P-1, 0 to P-1, 0 to P-1]

    Red, green, blue color image

    Like three grayscale images

    x(m,n) = index into color map.

    Color map = three column table with all possible colors

    Image index says which row in that table gives RBG

    valuesfor that pixel

    So long as table is known, very easy to store indices

  • Image Type

  • Difference between Indexed Image and

    RGB Image

    Indexed Image RGB Image

  • Important MATLAB commands

    imread: Read an image

    figure: creates a figure on the screen.

    imshow(g): which displays the matrix g as an image.

    pixval : turns on the pixel values in our figure.

    impixel(i,j): the command returns the value of the pixel (i,j)

    iminfo: Information about the image.

  • Converting between Data classes and

    Image types

    Converting between data classes

    Converting between Image classes to data classes

    Converting between Image classes

    Note : When converting between data classes, it is important to

    keep in mind the value range for each data classes should be in


  • Converting between data classes

    General syntax for converting data classes

    A = given data class

    B = data class in which we want to convert A

    B = data_class(A)

    Ex : A in uint8 and we want to convert in to double, then

    B = double(A)

  • Converting between data classes

    • Ex 1:double to unsigned integer of 8 bit

    A =


    >> B =uint8(A)

    B =


  • Converting between data classes

    Ex 2 : Double to unsigned integer of 8 bit

    A =


    >> B = uint8(A)

    B =


    >> C = -2.76

    C =


    >> D = uint8(C)

    D =


    Note : Here range of unsigned integer of 8 bits is [0 255]

  • Converting between data classes

    Rule for conversion

    Convert to ‘0’ all the values are less than ‘0’.

    Convert to 255 all the values are greater than 255

    Convert numbers between 0-255 to corresponding integer

    values. E.g.: 5.8 convert into 6

  • Converting between Image classes to data


    Conversion should perform necessary scaling for the toolbox

    to recognize the data as valid image data.

    Ex: im2uint8

    Function set all the value less than 0 to 0

    And set 1 all the value those are greater than 1

    Now image range is in [0 1]

    Multiplies 255 to all values and round off to integer.

    Now range is in [0 255]

  • Converting between Image classes to data


    Ex 3: image of class double to unsigned integer 8

    f =

    1.4897 0.6715 1.6302

    1.4090 -1.2075 0.4889

    1.4172 0.7172 1.0347

    >> g=im2uint8(f)

    g =

    255 171 255

    255 0 125

    255 183 255

  • Ex 4: unsigned integer8 to double

    >> h = uint8(h)

    h =

    26 67 12

    212 156 178

    23 45 67

    >> g = im2double(h)

    g =

    0.1020 0.2627 0.0471

    0.8314 0.6118 0.6980

    0.0902 0.1765 0.2627

  • Ex 4:

    Function im2double convert input image to double format in

    range [0 1].

    Divide all values by 255 (in case of uint8, if uint16 than divide

    by 65535)

    Range of image in double format must be [0 1]

    Function mat2gray convert any matrix to gray image of double

    data class.

  • Ex 5 : any matrix to image

    h =

    26 67 12

    212 156 178

    23 45 67

    >> g = mat2gray(h)

    g =

    0.0700 0.2750 0

    1.0000 0.7200 0.8300

    0.0550 0.1650 0.2750

  • Ex 6 : any matrix to binary image using threshold 0.6h =

    26 67 12

    212 156 178

    23 45 67

    >> g = mat2gray(h)

    g =

    0.0700 0.2750 0

    1.0000 0.7200 0.8300

    0.0550 0.1650 0.2750

    >> g=im2bw(h,0.6)

    g =

    0 0 0

    1 1 1

    0 0 0

  • Ex 6:

    Function im2bw(f,T) convert any image into binary image

    with threshold T.

    All the values less than T are set to 0

    All the values greater than T are set to 1

    First all values are converted into double and than threshold is


  • Some important function

    function convert input into Valid input Image data


    im2uint8 uint8 Logical,uint8,uint16 and


    im2uint16 uint16 Logical,uint8,uint16 and


    mat2gray double (in range [0,1]) Logical,uint8,uint16 and


    im2double double Logical,uint8,uint16 and


    im2bw logical uint8,uint16 and double

  • Converting between Image classes

    Important function

    gray2ind - intensity image to index image

    ind2gray - indexed image to intensity image

    rgb2gray - RGB image to grayscale

    rgb2ind - RGB image to indexed image

  • Ex 7: rgb image to gray

    >> f = imread('lenna.png');

    >> g = rgb2gray(f);

    >> subplot(1,2,1);imshow(f);


  • Array Indexing

    MATLAB support many powerful indexing scheme that

    simplifying array manipulation and improve the efficiency of


    For image processing toolbox

    Vector indexing

    Matrix indexing

    Images are represented in matrix.

  • Vector Indexing

    • Array of dimension 1xn : row vector

    • Array of dimension nx1 : column vector

    • First element will start from 1 not from 0 (zero)

    • Ex: consider following vector

    v = [3 8 2 7 5 9 1 4]

    Different commands for vector indexing

    1. v(3) = [3 8 2 7 5 9 1 4] = 2 % to access 3rd element

    2. V’ = produce column vector of “v”

    Note : transpose operator (.‘)

  • Vector Indexing(cont.)

    3. v(1:3) produce element from index 1 to 3

    v(1:3) = [3 8 2 7 5 9 1 4] = 3 8 2

    4. v(3:5) = [3 8 2 7 5 9 1 4] = 2 7 5

    5. v(end) = [3 8 2 7 5 9 1 4] = 4 % to access last element of array

    6. v(5:end) = [3 8 2 7 5 9 1 4] = 5 9 1 4 % to access 5th to last element

    7. v(: ) = produce column matrix

    8. V(1:2:end) = [3 8 2 7 5 9 1 4] = 3 2 5 1

    9. V([1 4 7]) = [3 8 2 7 5 9 1 4] = 3 7 1

    Note : index 1:2:end means start from 1 count up by 2 and end with last element. Steps can be negative,

    Ex.: V(end:-2:1) = [3 8 2 7 5 9 1 4] = 3 2 5 1

    Start with last element count down by 2 and end with first element

  • Matrix indexing

    Matrix can be written in MATLAB

    >> A= [1 2 3; 4 5 6; 7 8 9]

    A =

    1 2 3

    4 5 6

    7 8 9

    >> size(A) ; % to find dimention of matrix

    3 3

  • Matrix indexing(cont..)

    Examples for matrix indexing

    1. To extract element of 3rd row ,2 column

    A =

    1 2 3

    4 5 6

    7 8 9

    A(3,2) = 8

    Note : general format is A(row, column)

  • 2. To extract all element from 2nd row

    A(2,:) = 4 5 6

    3. To extract all element from 3rd column

    A(:,3) = 3



    4. to fetch top 2 row

    A(1:2,1:3) = 1 2 3

    4 5 6

    Same for to fetch last 2 column A(1:3, 2:3)

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