A Pixel-Weighting Method for Discriminating Objects of Different Sizes in an Image Captured from a Single Camera

Mookyung Park, Namsu Moon, Sangrim Ryu, Jeongpyo Kong, Yongjin Lee and Wangjin Mun

S1 Corporation, Korea

Customer site

Alarm signal

Centralized control office

Instruction

Visit

Security agent

Cost ∝ Number of visits

Security Service Flow

PIR sensor ( Passive Infra-Red )

False alarm Cost Cost ￪￪

Lacks intelligence

More IntelligenceVision sensor + Image processing

Stereo : expensive

Single : cost-effective

useful feature for discriminating objectsObject size

This talk is on a method of how to calculate the size of objects in an image captured from a single camera

Single : cost-effective

Objectives

< Surveillance space >

Object

< Image >

A AB C

B

C

< Surveillance space >

Object

< Image >

A AB C

B

C

Proper weight of pixel Real size of objects

Objects in the images

< Surveillance space >< Surveillance space >< Surveillance space >< Surveillance space > < Image >

pixel(x,y)

Hx,y

Hx,y-1

Vy

trapezoid

1,,, 2

1 yxyxyyx HHVA

Overview of Calculation

The object is standing perpendicularly to the ground and is not floating in the air.

1st.

The camera is installed at high location looking down objects like humans.

2nd.

3rd

.The camera kept in a horizontal position, not tilting to the right of the left.

The effect of radial distortion of lens does not appear in the image.

4th.

Assumptions

he

Blind zone

AB

AV

AV

H

1 2 3 HH-1

< Side view of the surveillance space >

he

Blind zone angle

Blind zone

AB

AV

AV

H

W1 2 3 HH-1

H

123

H-1H

Vertical pixel number

< Image >

< Side view of the surveillance space >

Blind zone

< Top view of the surveillance space >

Blind zone

< Top view of the surveillance space >

AH AH

W

1 2 3 W2

2 1W2

1 2 3W2

12W2

Even symmetryEven symmetry

Horizontal pixel number

Blind zone

< Top view of the surveillance space >

AH AH

W

1 2 3 W2

2 1W2

Camera lensHorizontal angle of view AH

Vertical angle of view AV

InstallationBlind zone angle AB

Height of Installation he

Image sizeHorizontal pixel number W

Vertical pixel number H

< Parameters >< Parameters >Height of Installation

Vertical angle of view

Horizontal angle of view

Parameters Required

AAx,yx,y = = ××VVyy × ( × ( HHx,y x,y + H+ Hx,yx,y--11 )

AV

H

AV

HXy

θy

< Image >

H

12

H

W

he

AB

AV

1bottomyd

yd

vy1 yyy LLV yyyy bottom

ddL tan1 y

ey

hd

tan

yH

AA VBy 90

Ly-1

Ly

1 yyy LLV

yyyy bottomddL tan1

y

ey

hd

tan

yH

AA VBy 90

ybottom

Cy

y

bottomy1bottomy θyθy

190tan

90tan190tan

bottomV

B

VB

VB

ey

yH

AA

yHA

AyHA

A

hV

1122

AAx,yx,y = = ××VVyy × (× ( HHx,yx,y ++ HHx,yx,y--11 )1122

Cy

y

yey

LhC

sin

y

yey

LhC

sin

θy

he

Ly

Cy

Cy

CyCy CyCy

< Image >

Pixel (x,y)

Dx-1,y

Dx,y

Hx,y

Hx,y-1

Vy

yxyxyx DDH ,1,,

xW

ACD Hyyx tan,

AH

W

AH

2

Cy

yxyxyx DDH ,1,,

xW

ACD Hyyx tan,

y

yey

LhC

sin

y

HHye

yx

xWA

xWA

h

H bottomy

sin

1tantantan

tan

1

,

kH

AAwhere

xWA

xWA

h

xWA

xWA

h

hA

VBk

y

HHye

y

HHye

yyeyx

bottomy

bottomy

bottomy

90,

sin

1tantantan

tan

sin

1tantantan

tan

tan

tantan

2

1

1

1

1,

1

1

1

Final Formula Representing the Weight

• Experimental set-up

Experimental Verification

Referenceimage

Currentimage

Difference Binarization

Noise FilterLabeling

Weighting

Experimental Results (1)

a

b

c

d

e

b 3 156 5574

c 4 108 5454

d 5 78 5306

e 6 62 5821

a 2 234 5241

Distance Pixels Weight sum

• For the same object

with different locations

• For objects of different sizes

Experimental Results (2)

Smallanimal

HumanSmall

animalHuman

a 88 88 2628 5761

Pixels Weight sum

b 56 186 2144 5682

c 35 339 2243 5919

a

b

c

Human

Small animal

Summary

Operational cost caused by false alarms can be significantly suppressed by adopting intelligent vision-based sensors in our security service business

Considering cost-effectiveness, we proposed a method of calculating the size of the object in the image captured from single camera

The calculation of object size requires parameters which are obtained when installing the vision sensor (camera)

Experimental results show that the proposed method produces a useful feature for distinguishing objects of different sizes