32 Digital Image Processing_1 (1)

8/8/2019 32 Digital Image Processing_1 (1)

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DIGITAL IMAGE WARPING

BY

V.INDIRA K.BHARGAVI

III/IV B.TECH III/IV B.TECH

07F21A0421 07F21A0410

ECE ECE

FROM

GATES INSTITUTE OF TECHNOLOGY

EMAIL:

[email protected]

[email protected]

Contact no:9000715735

9642115601


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ABSTRACT

Image warping is a transformation which maps all positions in a second plane. It

arises in many image analysis problems whether in order to remove optical distortions

introduced by a camera or a particular viewing perspective to register an image with a

map or to align two or more images. The choice of warp is a compromise between a

smooth distortion and one which achieves a good match. Matching can be specified by

points to be brought into alignment by local measures of correlation between images. The

warping process has wide applications in computer animation including distortion

compensation of imaging sensors, decalibration for image registration, geometrical

normalization for image analysis and display, map projection, and texture mapping for

image synthesis. Real time application of digital image warping in software

implementation has been designed named as Photo Mopher and Photo Warper.


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Introduction

This paper concern itself with the field of image warping. The following sections

serve as a short introduction to the field and its applications. The term image warping

refers to the process of geometrically transforming two dimensional pictures or images.

Although the word warp may seem to suggest a radical distortion, the term image

warping encompasses the whole range of transformation from simples one such as

scaling or rotation complex irregular warps. Geometric image transformations performed

by optical or mechanical means could conceivably be considered cases of image warping,

but in practice the term is used specifically for transformation performed by electronic

and especially by digital means. This paper mainly addresses methods for performing

image warping by means of software and hardware implementation.

a) Original Image b) Warped Image

The above images shows that how the pixels of the first image (original image) has been

transformed to create a warped image (second image) by performing image warping

using general purpose software implementation of digital computer.


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What Exactly is Image Warping?

The image warping is defined as the Geometrical Transformation of two

dimensional pictures or images. An image warp is defined by a mapping from the

coordinate space of a source image (u,v) to the coordinate space of a destination image

(x,y). It is a transformation which maps all positions in one image plane to positions in a

second plane.

It arises in many image analysis problems whether in order to remove optical

distortions introduced by a camera or a particular viewing perspective to register an

image with a map or template or to align two or more images. Digital image warping is a

growing branch of image processing that deals with geometric transformation techniques.

It has benefited greatly from several fields ranging from early work in remote sensing to

recent development in computer graphics.

IMAGE FLOW GRAPH OF DIGITAL IMAGE WARPING


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EXAMPLE OF IMAGE WARPING

a) Mouse button is pressed b) Defining radius

c) Radius defined d) Defining strength

e) Another warp f) Final result


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PIXELS TRANSFORMATION IN IMAGE WARPING

Warping an image amounts to applying a coordinate transformation (warp) to the image

plane and resampling to the grid.

TYPES OF MAPPING IN IMAGE WARPING

Forward Mapping: It works like a movie projector that projects an image on to a flat

screen. Each pixel in the source image is mapped in to the target image.

Reverse Mapping: It takes each target locations and determine which pixels in the

source image are required to create the target pixel.

a) Forward Mapping b) Reverse Mapping


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HARDWARE IMPLEMENTATION OF DIGITAL IMAGE WARPING

Images that skewed or stretched by poor scanning or planar projection or distorted

around the edges by a suspect lens or atmospheric effect are especially problematic with

finely calibrated inspection system will not be a problem in hardware implementation of

digital image warping using Mini Warper.

Diagram of Mini Warper

Mini Warper provides the ability to perform operations using "bi-quadratic"

equations that permit separate, second-order warping of each axis, supporting the affine

warps as well as some of the higher-order warping operations. Mini Warper can also

accept externally generated warping addresses, permitting warps of arbitrary order.


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Mini Warper includes the components shown in the simplified Image Flow element flow

diagram (figure1) to perform this backward mapping. One megabyte of image memory

(WX_MEM) is accessed through a single 20 MHz gateway. This gateway can either

receive (WX_RCV) or transmit (WX_XMT), setting the effective throughput to 10 MHz.

An internal address generator (WX_ADDRGEN) can evaluate second-order transforms

to within 1/16 of a pixel on the source image. WX_ADDRGEN can also be bypassed

with the WX_ADDR_SRC multiplexer, allowing source location addresses to be

supplied externally to support arbitrary warping operations. The resulting address

controls three MOSCs that regulate the availability of image data, the need for blanking

values from WX_K0, and the operation of a dynamically adjustable FIR filter

(WX_IMAC). This performs interpolation on a two-by-two neighborhood around the

source location to remove the typical aliasing and blockiness of zoomed images.

APPLICATION OF MINI WARPER

Demonstration program creates a flag waving special effect from continuously

acquired data using mini warper.


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APPLICATIONS OF DIGITAL IMAGE WARPING

The applications of digital image warping are many and diverse. Almost

any application of digital image processing involves at least an occasional need to change

the location, scale or orientation of the image. All these operations are simple instances of

image warping.

One of the oldest and still one of the most important applications of digital image

warping is in remote sensing. Photographs taken from aircraft or satellites suffer

from a number of geometric distortions caused by lens imperfections, perspective,

curvature of the earth etc. Digital image warping is used in correcting these

distortions and in aligning multiple overlapping images.

In the field of three-dimensional computer graphics, a technique called texture

mapping is used to give models of three-dimensional objects a more natural

appearance by mapping two-dimensional textures onto their surfaces to simulate

features like wool grain or surface bumpiness. When these three-dimensional

objects are then rendered on a two-dimensional display, the overall effect is that

of a mapping from the two-dimensional texture space to the two-dimensional

screen space, i.e., an image warp.

Image warping is also increasingly being used as an artistic tool. Most software

packages for painting and photo retouching contain at least some king of image

warping facilities and/or warping-based special effects.

Recently, much attention has focused on a special effects technique known as

morphing (from metamorphosis, although the technique apparently predates the

term). In morphing, image warping techniques are combined with key-frame


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animation and cross-fading to create a convincing illusion of one object

transforming smoothly into another. Morphing has been used as an element in

many recent motion pictures, music videos and television commercials.

INSTRUMENTAL APPLICATION OF DIGITAL IMAGE WARPING

MIRROR METHOD

The basic approach is to design a mirror and capture the image reflected from it.

The basic setup is shown below, the "final camera" is the one being used with the

mirror, the "test camera" is used for testing purposes, it may be a wide angle or

angular fisheye if that is supported. Of course the magic is in the design of the mirror

which creates an image so that when projected through the hardware gives the.

correct view. In this case the lens has been calculated so as to work with an

orthographic (parallel) projection.

EXPERIMENTAL SET UP


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MIRROR WARPING OF A ROOM

RECENT TRENDS IN DIGITAL IMAGE WARPING

1. MOTION COMPENSATED VIDEO SEQUENCE

INTERPOLATION USING DIGITAL IMAGE WARPING

A novel method for temporal interpolation of sequence is proposed. The motion

vectors are estimated on sparse grids and image warping techniques are applied to

obtain the interpolated frame the advantages of the proposed method are its ability to

compensate for complexity when implemented in the coder complex motion types

such as scaling or rotation and the low complexity when implemented in the coder

using warping based prediction.

The advantage of the proposed method is that it can compensate for various

motion types such as translations, rotations and scaling. It is also used to increase the

frame transfer rate of the video recorder.


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a) Previous Image b) Current Image

It is showing the motion compensated prediction of the current frame by warping

the previous frame. The motion compensated warps are obtained by tracking the

motion of the selected points known as grid points. The areas of the previous image

defined by the grid points are individually transferred to their corresponding areas in

the current image.

It is showing the frame interpolation using motion compensating warping.

2. IMAGE REGISTRATION PARAMETER TUNING AND

APPROXIMATE . FUNCTION USING THE DIGITAL IMAGE WAING

Image registration is the process of aligning or overlaying two similar images taken at

different times, different sensor angles or with different sensors. A difference can be


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produced by subtracting the two registered images. This image contains information

regarding the changes between scenes and useful in fields such as machine vision,

remote sensing and medical imaging.

The below figure shows the application of Digital Subtraction Angiography.

Two x-ray images of a patients chest, one taken after and one taken before

contrast injection are subtracted to yield the difference image showing the

patients arteries.

The below block diagram shows the structure of the image acquisition, control

point selection image registration and subtraction system. R is the real world

image which enters the image acquisition system. U* is introduced by the

imaging hardware to produce the distorted image S, it is applied to the control

panel which contains a rough set of similar points between the t E is the input to

the registration module which needs asset of control points. Tuning block adjusts

the tie points on the image until there is a best fit between two images.


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.

Then it is given to the result module which is producing distortion free difference

image.

The below graph shows the cost function analysis which produced the best results

and this can be used to produce a cost function for computation analysis.

GENETIC ALGORITHM

For image registration an algorithm is proposed known as Genetic Algorithm.

begin

t=0

initialize population p(0)

evaluate population p(0)


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while termination criterion not satisfied

do

begin

t=t+1

select p(t) from p(t-1)

recombine p(t)

evaluate p(t)

end

end

3. A FUZZY APROACH TO DIGITAL IMAGE WARPING

A new algorithm uses fuzzy techniques to warp polygons that have different

locations, orientations, sizes and no. of vertices. The fuzzy warping methods presented

here smoothly transform a source polygon in to target polygon. The method uses a fuzzy

vertex correspondence technique to establish the correspondence between the vertices of

the source and target polygons and a fuzzy transformation technique to interpolate both

the vertices and orientations of the polygon to produce the image between them.


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The above figure shows how a circle is transformed to hexagon polygonally by using

fuzzy approach of digital image warping.

CONCLUSION:

This thesis has reviewed the fundamental theory, methods and applications of

image warping. The main contribution of the thesis is the design of new kind of highly

interactive image warping system aimed at creative graphic design applications. The

feasibility of this approach is demonstrated in an implementation and performance

measurements indicate that current work station computer are fast enough for real time

warping of areas of several hundred pixels across.

REFERENCES:

G. Wolberg Digital Image Warping

R. Thoma and M. Bierling Image Communication

T. Bier Image Metamorphosis

G. Pagliari Image Registration

D. Goldberg Genetic Algorithm


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32 Digital Image Processing_1 (1)