Measurement of a parameter associated with motion of an
object
The present invention relates to a method and an apparatus
for measuring a parameter associated with motion of an
object.
Optical measurement techniques have typically been employed
to measure parameters associated with motion of moving
objects. For measuring parameters of moving objects, images
of the moving objects are captured and, thereafter, the
captured images are processed to compute the parameters.. The
parameters are computed by determining the positions of the
objects in different images at varying time instances.. for
example, displacement may be computed as a difference in
positions of individual objects between two images. Velocity
may be computed as a ratio of displacement and time
difference between the capturing of the two images.
Acceleration may be computed as a ratio of difference in
velocity of the objects between two images and time
difference between the capturing of the two images.
To capture images of fast moving objects, high speed cameras
are needed, such that, the objects are captured in the
subsequent frame prior to the objects moving out of field of
view. High speed cameras add to the overall coat of the
measurement apparatus and require additional coaling
provisions.
It is an object of the invention to eliminate or at least
minimize the above mentioned problems.
The above object is achieved by a method of measuring a
parameter associated with motion of an object, wherein the
method comprises illuminating an object using at least two
light sources, the at least two light sources emitting light
of distinct colours, wherein each of the at least two light
sources are strobed at a respective delay, capturing
reflected light from the oblect to result into one image of
the object, the image comprising at ieast two distinguishable
colour chain els capable of distinguishing the distinct
colours of the light and processing the image to compute a
parameter associated with motion of the object from position®
of the object in the at least two distinguishable colour
channels of the image.
Thereby, enabling measurement of parameters associated with
motion of an object moving at a high speed using inexpensive
cameras.
According to an embodiment, each of the at least two light
sources are strobed for a predetermined on-time at the
respective delay, wherein the respective delay is
predetermined.
This enables capturing of plurality of colour channels of '%tm
moving object at varying time instances in one image,
According to yet another embodiment, each of the at least two
light sources are strobed for a predetermined on-time at the
respective delay from a reference trigger.
This enable- in deriving the time of strobing of each light
source.
According to yet another embodiment, the at least two light
sources are selected from the group consisting of a red llfjit
source, a green light .source, and a blue light source.
fhts enables capturing the reflected light from the object to
result into an image as the object may comprise at least one
of the principle colours.
According to yet another embodiment, the parameter associated
with motion of the object is one of the group consisting of a
displacement, a velocity, and an acceleration
According to yet another embodiment, the displacement is
computed as the distance between positions of the object in
two color channels of the at least two distinguishable coloat
channels oi the image.
According to yet another embodiment, the displacement is
computed using a pattern matching algorithm.
Thereby, providing greater accuracy in environments where
parameters associated with motions of a plurality of objects
are measured.
According to yet another embodiment, the pat-tern marching
algorithm is a point-set matching algorithm.
According to yet another embodiment, the computing of the
displacement using the point-set matching algorithm includes
obtaining position information of the object in two colour
channels oi the at least two colour channels of the image,
reducing the object in the two color channels of the at least
two colour channels of the image to a point to obtain point
sets, mappring the corresponding points of the object in the
point sets of the two color channels of the at least two
colour channels of the image, and computing the displacement
of the object as a distance between corresponding points of
the object in the point sets of the two colour channels of
the at least two color channels of the image.
According to yet another embodiment, the point represents a
centre of the object.
According to yet another embodiment, the computing of the
displacement for the object comprising portions of at least
two principle colours using the point-set matching algorithm
includes obtaining position information of portions of the
object in two colour channels of the at least two colour
channels of the image, reducing the portions of the object in
the two colour channels of at least two colour channels of
the image to points to obtain point'sets, mapping the
corresponding points oi" the portions of the object in the
point sets -of. the two color channels of the at least two
colour channels of the image, determining centers of the
object in the two colour channels of the at least two colour
channels of the image from the point sets representing the
portions of the object in the two color channels of the at
least two colour channels of the image, and computing the
displacement of the object as a distance between
corresponding centers of the objects in the. two colour
channels of the at least two color channels of the image.
According to yet another embodiment, the points of the
portions of the object represent centers of the portions of
the object.
According to yet another embodiment, the obtaining of
position information of the object in each of the plurality
of colour channels is performed using a template matching
algorithm.
According to yet another embodiment, the determining of
centers of the object in each of the at least two colour
channels of the image from the point sets representing
portions of the objects in each of the at least two colour
channels of the image in the frame is derived by offsetting
from the pconts of the portions of the objects.
According to yet another embodiment, the velocity of the
object is computed as a Eatio of the displacement of the
object and a time difference of strobing light sources
associated to the colour channels of the image.
According to yet another embodiment, the acceleration of the
object is computed as a ratio of difference between a
velocity (vie,) of the object during its motion from a ftest
colour channel to a second colour channel and a velocity
(vtB) of the object during its motion from the second colour
channel to a third colour channel and difference between a
time (ts) of strobing the second light source associated with
the second colour channel and a time (tB) of strobing the
third light source associated with the third color channel.
Another embodiment includes an apparatus for measuring a
parameter associated with motion of an object, wherein the
system comprises an illuminating system comprising at least
two light sources, the at least two light sources emitting
light of distinct colours, wherein each of_the at least two
light sources are strobed at a respective delay, a colour
camera to capture reflected light from the object to result
into one image of the object, the image comprising at least
two distinguishable colour channels capable of distinguishing
the distinct colours of the light, and a processor to process
the image to compute a parameter associated with motion of
the object from positions of the object in the at least few©
distinguishable colour channels of the image.
Thereby, eliminating the need of expensive high speed cameras
for measuring parameters associated with motion of an object
moving at a, high speed.
The present invention is further described hereinafter with
reference to illustrated embodiments shown in the
accompanying drawings, in which:
FIG 1 illustrates an apparatus for measuring a
parameter associated with motion of an object
according to an embodiment here,
FIG 2 illustrates a timing diagram of strobing the
Light sources in accordance to an embodiment of
the invention,
FIGS 3a-3c illustrates examples of reflected light of
distinct colours from an object captured in
distinguishable colour channels of an image,
FIG 4 illustrates an example of a composite image
comprising the colour channels of Fig 3a thrategto
Fig 3c according to an embodiment herein,
FIG 5a-5b illustrates point sets of a plurality of objects
in two distinguishable colour channels ac0o£4tag
to an embodiment herein,
FIGS 5c illustrates mapping of points of objects in point
sets of two colour channels according to an
embodiment herein,
FIGS 6 illustrates a flow diagram illustrating a methoet
of computing displacement of a plurality of
objects using a point-set matching algorithm;
according to an embodiment herein,
FIG 7a illustrates an example of an image of an dfeject
comprising portions of the three principal
colours and imaged in white light,
FIGS 7b~7d illustrates colour channels of an object
.illuminated by red, green and blue colour light
sources respectively,
FIGS 8a-8h illustrates the creation of point sets for a
plurality of objects comprising portions of
principle colour components of red, green and
blue using a point-set matching algorithm
according to an embodiment herein.
FIG 9 i Llustrates mapping of the points of portions of
corresponding objects in the colour channels of
the image,
FIG 10 illustrates a flow diagram illustrating a method
tor determining the displacement of a moving
object comprising portions of principle colour
components,of red, green and blue using a point-
set matching algorithm according to an embodiment
herein, and
FIG 11 illustrates a flow diagram illustrating a method
of measuring a parameter associated with motion
of an object according to an embodiment herein:.
Various embodiments are described with reference to the
drawings, wherein like reference numerals are used to refer
to like elements throughout. In the following description,
for purpose of explanation, numerous specific details are set
forth in order to provide a thorough understanding of one ©:r
more embodiments. It may be evident that such embodiments may
be practiced without these specific details.
FIG 1 illustrates an apparatus for measuring a parameter
associated with motion of an object in accordance with an
embodiment of the invention. The apparatus 11 comprises an
illuminating system 12 to illuminate the object, a colour
camera 13 to capture the image of the moving object, and an
image processing means 14 to compute a parameter associated
with motion of the object. The parameter of moving object
measured herein includes, but not limited to, displacement,
velocity and acceleration.
In the shown example of FIG 1, the illuminating system 12
comprises it least two light sources, wherein the light
sources emit light of distinct colours. The light sources are-
selected from the principle colours red, green and blue. Each:
of the light sources is strobed at a respective predetermined.
delay for a respective predetermined on-time. In an
embodiment, the; light sources may be strobed at the
respective 'redetermined delay from a reference trigger, The
object shai: reflect the light projected on it by the light
sources for the respective predetermined on-time. For
example, the object illuminated using an illuminating system
(12) comprising three light sources, such as, a red light
source, a gieen light source and a blue light source will
reflect red colour light, green colour light and blue colour
light respectively.
The colour camera 13 is exposed for the entire duration of
strobing of the light sources, and thus, captures the
reflected .light of distinct colours from the object in one
image comprising distinguishable colour channels. The image
obtained is a composite image comprising the plurality of
colour channels. For an example, the number of colour
channels in an image is equivalent to the number of light
sources illuminating the object. Therefore, the composite
image compr.; ses the colour channels that are capable of
distinguishing the distinct colours of the light emitted by
the light sources, for example, the red, green, and blue
colours. Thus, illuminating the object with light sources
emitting light of distinct colours and exposing the camera 13
for the entire duration of strobing of the light sources
enable capturing the distinct colours of light reflected by
the object at varying instances of time into one image.
Capturing the reflected light of distinct colours from the
object at varying instances of time in one image allows
imaging of an object moving at a very high speed. The
capturing of.' the reflected light from the object in colour
channels capable of distinguishing the distinct colours of
light enable determining the position of the object at
varying instances of time.
In an embodiment, the image processing means 14 comprises a
processor 1.5 operationally coupled to a memory 16, The
processor 15 processes the image captured by the camera 13 to
compute the parameters of the moving object by determining
the positions of the object in the different colour channels
of the imago*. The memory 15 may comprise stored therein an
algorithm to determine the displacement of the moving object.
The distance between the positions of the object in different
colour channels is determined. This distance between the
positions of the objects in two colour channels of the image
provides the displacement of the object. For an example, the
distance between the positions of the object in two colour
channels may be computed as the distance between the centers
of the object in two.color channels. As velocity is a ratio
of displacement, and time, the ratio of the displacement of
the object and a time difference of strobing the light
sources for which the emitted light has been captured in the
respective color channels of the image which have been
considered for determining the displacement of the object
provides with the velocity of the object. In order to measure
velocity of the moving object, it is required to measure the
displacement of the moving object. Displacement may be
measure as a distance between positions of the objects in two
color channels of the image. Thus, velocity of the moving
object may be computed by processing an image comprising two
colour channels. Accordingly, to determine velocity of the
moving object, the illuminating system 12 may comprise two
light sources producing light of distinct colours.
However, in according with some embodiments of the invention,
to measure acceleration, an illuminating system 12 comprising
three light sources is used, such as to capture the light
reflected from the moving object at three different instances
of time into an image comprising three distinguishable colour
channels. The position of the object in the three colour
channels of the image provide two displacement vectors using
which the acceleration of the object may be computed.
FIG 2 illustrates a timing diagram of strobing the light
sources in accordance to an embodiment of the invention. In
the example of FIG 2, the timing diagram illustrated is for
an illuminating system (12} comprising three light sources,
As shown in the example of FIG 2, each of the light sources
is trigged at a delay from a failing edge of the reference
trigger 21 which is t,»?f. The reference trigger 21 is stroked
at a delay is-:io!^. A first light, source is strobed after a
delay tR from tret for an on-time wR. A second light source is
strobed after a delay t& from ttBt for an on-time wG. A third
light source is strobed after a delay t3 from tief for an on-
time wB, The camera 13 of FIG 1. is exposed for a time ts from
tref, such that the reflected light form the object due to the
illumination of the object using the light sources is
captured in a single image. For an example, the first light
source may be a red light source, the second light source may
be a green light source and the third light source may be a
blue light source. The on-time wR, ws and wB and the delays t»,
tG and t& may be adjusted depending on the field of
application. For example, for measuring parameters of very
fast moving objects the delays may be decreased and for
measuring the parameters of slow moving objects the delays:
may be increased.
FIG 3a through FIG 3c illustrates examples of reflected light
of distinct colours from an object captured in
distinguishable colour channels of an image. FIG 3a
illustrates the reflected light of red colour 31 from the
object in a red colour channel of an image. FIG 3b
illustrates the reflected light of green colour 33 from the
object in green colour channel of an image and FIG 3c
illustrates the reflected light of blue colour 35 from the
object in a blue colour channel of an image. As the light
sources are strobed at varying time interval, the respective
reflected light 31, 33, 35 from the moving object captured in
respective colour channels of the image provides the
positions of the object at varying instances of time. As the
camera 13 of FIG 1 is exposed for the complete time interval
of strobing the light sources, the reflected light 31, 33, 35
are captured in the respective colour channels in oris image
of the camera 13, and thus, resulting into a composite image.
FIG 4 illustrates a composite image 40 comprising the colour
channels of FIG 3a through FIG 3c. As illustrated in FIG 4,
the composite image 40 comprises the colour channels of FIG
3a through FIG 3c and thus the reflected light 31, 33, 3S
from the object in the respective colour channels are Been-,
The difference in positions of the object between the two
colour channels provides the displacement of the object. Fcjr.
example, the difference between the positions of the object
in the red and green color channels shall provide the
displacement, of the object with respect to. the initial
position of the object at red colour channel, h displacement
vector 41 between the positions of the object, i.e.,
reflected light 31, 33 of the red and green color channels.,
is computed as the difference between the initial position Of
the object at the red colour channel and the final ppsitliOh
of the object at the green colour channel. Similarly, a
displacement vector 43 between the positions of the; object at
green and blue colour channels is computed as the difference
between the initial position of the object at the green
colour channel and the final position of the object at the
blue colour channel. Velocity of the object is computed the
ratio of th<-> displacement of the object and a time difference
of strobing the light sources for which the emitted light has
been captured in the respective color channels of the image
which have been considered for determining the displacement
of the object. Acceleration being the rate of change of
velocity me-v be computed using velocity of the object
determined at two different time instances, for example the
velocity of the object during its motion from the position at
the red colour channel to the position at the green qoloua*
channel and the velocity of the object during its motion, from
the position at the green colour channel to the position at
the blue colour channel. Thus, in the shown example of FIG 4.,
acceleration may be computed using the formula:
where a is the acceleration of an object, vtl is the velocity
of the object at a first instance, vt2 is the velocity of the
object at a second instance, tl is the time at first the
instance an-:; t2 is the time at the second instance.
For the embodiments described herein, the formula (1) may b#
expressed as:

where a is the acceleration of the object, vts is the
velocity of the object at a second colour channel (for
example the green colour channel), v-ta is the velocity at &
third color channel (for example the blue colour channel), t$
is the time of strobing the second light source (for example
the green light source) and tB is a time of strobing a third
light source (for example the blue light source).
For applications involving a large number of objects, the
displacement of the objects may be computed using a pattern
matching algorithm stored in the memory 16 of FIG 1. The
pattern matching algorithm is used for determining the
displacement of the objects. The pattern matching algorithm,
typically, uses a template matching algorithm to compare the
pattern of the objects in the template-with the objects in
each of the colour channels of the image and identifies the.
positions of the objects having the highest similarities with
the pattern in the template. The template matching algorithm
identifies the position of the objects considering the
rotation, i..e., orientation of the object-with respect to the
pattern of the template. A distinct template is used for each
colour channel of the image and instances of the template Sre;
searched for in the image. This provides the positions of the
objects in the image that match to a particular pattern of
the template, i.e., positions of the objects in a colour
channel at a particular instance. Thus, by determining the
positions of the object? in the image in each of the colour
channels, p-sition of the moving objects at varying time
instances exe obtained. In an embodiment, the pattern
matching algorithm used is a point-set matching algorithm.
However, it should be apparent to a person skilled in the art
that other pattern matching algorithm, known in the art, may
also be used to determine the displacement and orientation of
the objects.
Referring now to FIG 5a and 5b, there are shown point sets
51, 53 of a plurality of objects in two distinguishable
colour channels obtained using a point-set matching
algorithm. For each distinguishable colour channel present in
the composite image, a respective point set is created to
obtain the positions of the objects in that colour channel.
To create a point set of the objects in a color channel, a
template matching algorithm is used for each colour channel
and instances of the template are searched for in the
composite image comprising the colour channels. The template
matching algorithm provides position information of the
objects similar to the template in the composite image. The
point sets are created using the positions of the detected
objects. Each object in the colour channel of an image is
reduced to a point in the point set. The point sets 51, 53
comprises points of objects detected using the template
matching algorithm for the respective colour channels of an
image. For mapping the corresponding points of the object in
different color channels an iterative point-set matching
algorithm '¦ <~ used. The point-set matching algorithm maps the
corresponding points of the object in point sets of the
eo.:lour channels and computes the displacement of the objects,
i.e., where each point has moved as illustrated in point set
55 of FIG 5c. The displacement of the object is computed
using the point-set matching algorithm by preserving the
structural information between points.
FIG € illustrates a flow diagram illustrating a method of
computing displacement of a plurality of objects using a
point-set matching algorithm. At block 61, position
information of the objects is obtained in two colour channels
of the at least two colour channels of the image. Next, at
block 62, trie objects in the two colour channels of the at
least two colour channels is reduced to a point to obtain
point sets. At block 63, the corresponding points of the
object in the point sets of the two colour channels of the at
least two colour channels of the image are mapped. Moving
next to block 64, the displacement of the object is computed.
as a distance between corresponding points of the object in
two colour channels of the image.
Preferably, the position information of the objects in two
colour channels is obtained using a template matching
algorithm.
The techniques described above can be used to compute
velocity of an object if the object comprises at least two
principle colours of red, green and blue. For the computation
of acceleration of an object, the object should comprise the
three principle colours of red, green and blue. However, the
principle colours need not be present in equal strengths or
in any part icuiar format . Fief erring now to FIG 7a, an example
of an image of an object comprising the three principal
colours and imaged in white light is. shown. In the example of
FIG 1&, a portion 71 of the object is of blue colour, a
portion 73 of the object is of green color and a portion 75
of the object is of red color. However, in accordance with
the embodiments of the invention, when the object is imaged
using the illuminating system {12} comprising the light
sources of principle colours, such as red, green and blue.,.
only the portion that corresponds to the color of the light
source shall reflect the light. Therefore, only the light
reflected by the portion of the object corresponding to the
colour of the light source is captured in the image for the
particular colour channel. FIG 7b through 7d illustrates the
colour channels of the object illuminated by red, green ani
blue colour light sources respectively. As the object
comprises the principle colours of red, green and blue, the
portion of the object corresponding to the colour of the
light source is only visible in a colour channel. For
example, in the: red colour channel illustrated, in FIG 7b,,
only the rec portion 7 5 of the object is seen, as only the
red portion 75 of the object is capable o.f reflecting red
light when the object is illuminated using a red light
source. Similarly, in the shown example of FI© 7c only the
portion 7.3 of the object is visible when the object is
illuminated using a green light source and in the shown
example of FIG 7d only the portion 71 of the object Is
visible when the object is illuminated using a blue light
source. Therefore, in the present embodiment, the image of
the object in a particular colour channel is used as a
template for the colour channel in the template matching
algorithm to determine the positions of the objects in the
colour channel. Thus, the image of the object in a particular
colour channel is the object's color signature in that
principal colour component.
FIG 8a through. 8h illustrates the creation of point sets' fror
a plurality of objects comprising the principle colour
components of red, green and blue using a point-set thatching
algorithm. Referring now to FIG 8a, a composite image of a
plurality ci moving objects comprising portions of principal
colour components of red, green and blue is shown. For an
example, the portion 81 of the objects is of red colour, the
portion 02 of the objects is of -green color and the portion
83 of the crjects is of blue colour. FIG 8b shows the image
of the objects in a red colour channel when the objects are
illuminated by the red light source. It can be seen that only
the portions 8.1 of the objects are visible as the portions 81
of the objects are of red colour and are capable of
reflecting the red colour light. Similarly, FIG Be shows the
Image of the objects in a green color channel when the;
objects are illuminated by the green light source and FIG 84
shows the image of the objects in a blue colour channel when
the objects are illuminated by the blue light source. It Can
be seen in FIG 8c that only the portions 82 of the objects
are visible as the portions 82 of the objects are of green
colour and are capable of reflecting green colour light and
in FIG 8d only the portions 83 of the objects are visible a$
the portions 8 3 of the objects are of blue colour and. are
capable of reflecting blue colour light. The template, for
determininq the position of the objects in each colour
channel is the colour signature of the objects for that
principal colour component. Referring now to FIG 8e, a colour
signature h4 is used as a template for the red colour
channel, a colour signature 85 is used as the template for
the green colour channel and a colour signature 86 Is used &s
a template for the blue colour channel. The colour signa £«¦.£©.£
84, 85, 86 are used to locate positions of the portions 81,
82, 83 of the objects respectively in the respective colewar
channels of the composite image. The template, matching
algorithm determines the position of the portions 81, 83?., #:3
considering the orientation of the objects with respect to;
the pattern of the template. Point sets are created using tsjhte
positions of! the detected portions 81, 82, 83 of the object*.
FIG 8f though FIG 8h illustrate the point sets for the red:,,
green and blue colour channels respectively. The detected
portions of the objects in a colour channel are reduced to
points to obtain the point sets.
The point-set matching algorithm maps the corresponding
points of the portions of the objects in different color
channels. The point-set matching algorithm locates the point si
of the portions of the objects in different color channels
and thereafter determines the centers of the object to
computes the displacement of the objects.
FIG 9, illustrates mapping of the points of the portions of
the corresponding objects in the colour channels of the
image. Displacement of the objects is computed as the
difference in positions of the objects in two colour
channels. The points in the point sets provide the centers &¦£
the corresponding portions of the objects. Knowing the centre
of a portion of the objects, the centre of the objects can be
computed by offsetting from the known center of the portions
of the GDiec'ts. Thereafter, displacement of the objects can
be computes a? the difference between the centers of objects
in two colour channels. The displacements of the objects £r.dm
a red color channel to a green color channel are illustrated'
as displacement vector 91 and the displacements of the
objects from a green color channel to a blue colour channel
are illustrated as displacement vectors 93. Velocity of the
objects may be computed as a ratio of the disp lacement and
the time d-i f ference of strobing the light sources associated
with the colour channels considered for computing the
displacement.
In an embodiment, the centers of the objects in a colour
channel may be determined from the known position of the
points of the objects by offsetting from the known position
of the portion of the object. The values for offsetting may
toe predetermined from the dimensions of the object.
FIG 10 illustrates a flow diagram illustrating a method -for
determining the displacement of a moving object comprising
the principle colour components of red, green and blue using
a point-set matching algorithm. At block 1001, position
information of portions of the object in two colour channels
of the at least two colour channels of the image is obtained.
Next, at block 1003, portions of the object in the two colour
channels of the at least two colour channels of the image are
reduced to points to obtain point sets. Moving to block 10.0:5,
the corresponding points of the portions of the object are
mapped in the point sets of the two color channels of the at
least two colour channels of the image. At block 1007,
centers of the object in the two colour channels of the at
least two colour channels of the image from the point sets
representing the portions of the object in the two color
channel of the at least two colour channels of the image.
Next, at block 1009, the displacement of the object is
computed as a distance between corresponding centers of the
object in tne two colour channels of the at least two color
channels of the image.
FIG 11 with reference to FIG 1 through FIG 10, illustrates a
flow diagram illustrating a method of measuring a parameter
associated with motion of an object according to an
embodiment herein. At block 1101, the object is illuminated
with at least two light sources, wherein the at least two
light sources emit light of distinct colours and each of th©
light sources are strobed at a respective delay. Next, at
block 1103, the reflected light from the object is captured
to result into one image of the object, wherein the image
comprises at least two distinguishable colour channels
produced by the at least two light sources. Moving next to
block 11Q5, the captured image is processed to compute a
parameter associated with motion of the ofojedt from positions
of the object in the at least two distinguishable colour
channels of the image.
Preferably, the light- sources are strobed for a predetermined
on-time at the respective delays from tmr, wherein the
respective delay may be predetermined. Additionally, the at
least two .Tight sources are selected from the group
consisting of a red light source, a green light: source, and a
blue light source. Moreover, the parameter associated with
motion of the object is one of the group consisting of a
displacement, a velocity, and an acceleration. The
displacement may be computed as the distance between cent-erg
of the objects in. two color channels of the ifftage in the
frame or by using a point-set matching algorithm.
Preferably, the velocity of the object, may be computed a§ a
ratio of the displacement of the objects and a time
difference of strobing light sources associated with the
colour channels of the image. Additionally, the acceleration
of the object may be computed as a ratio of difference
between a velocity |vtu of the object during its motion front
a first col cur channel to a second colour channel and a
velocity (v.) of the object during its motion from the
second colour channel to a third colour- channel and
difference between a time difference (tl) of strobing a first
light source associated with the first colour channel and a
second light source associated with the second colour channel
and a time difference (t.2) of strobing the second light
source associated with the second colour channel and a third
light source associated with the third colour channel.
Thus, the embodiments described herein enable determining
parameters such as displacement, velocity and acceleration of
an object moving at a high speed using a relatively less
expensive camera. Moreover, accuracy of the parameters
measured is relatively high. Additionally, the techniques
described herein eliminate the requirement of high speed
cameras, which are bulky and need external cooling systems,
for capturing images of object moving at a high speed.
While this invention has been described in detail with
reference to certain preferred embodiments, it should be
appreciated that the present invention is not limited to
those precise embodiments. Rather, in view of the present
disclosure which describes the current best mode for
practicing the invention, many modifications ana variations
would present themselves, to those of skill, in. the art
without departing from the scope and spirit of this
invention. The scope of the invention is, therefore,
indicated by the following claims rather than by the
foregoing description. All changes, modifications, and
variations coming within the meaning and range of equivalency
of the claims are to be considered within their scope.
We claim:
1. A method of measuring a parameter associated with
motion of an object, said method comprising:
Illuminating an object usinq at least two light sources,
said'at least two light sources emitting light of distinct
colours, wherein each of said at least two light sources
are strobed at a respective delay,
capturing reflected light, from said object to result into
one image of said object, said image comprising at least
two distinguishable colour channels capable of
distinguishing the distinct colours of the light, and
processing said image to compute a parameter associated
with motion of said object from positions of said object
in said at least two distinguishable colour channels .of
said image.
2. The method according to claim 1, wherein each of &aid
at least two light sources are strobed for a predeteKBiih^d
on-time at said respective delay, wherein said respective
delay is predetermined.
3. The method according to claim 2, wherein each of said
at least two light sources are strobed for a predetermined
on-time at said respective delay from a reference trigger
(21) .
4. The method according to claim 1, wherein said at least
two light sources are selected from the group consisting
of a red light source, a green light source, and a blue
light source,
5. The method according to claim 1, wherein said parameter
associated with motion of said object is one of the group
consisting of a displacement, a velocity, and an
6. The method as claimed in claim 5, wherein said
displacement is computed as the distance between positiofis
of said object in two color channels of said at least two
distinguishable colour channels of said image.
7. The merhod according to claim 5, wherein said
displacement is computed using a pattern matching
algorithm.
8. The method according to claim 7, wherein said pattern
matching algorithm is a point-set matching algorithm.
9. The method according to claim 8, wherein the
computation of said displacement using said point-set
matching algorithm includes:
obtaining position information of said object in two
colour channels of said at least two colour channels of
said image,
reducing said object in said two color channels of said sfe
least two colour channels of said image to a point to
obtain point sets,
mapping the corresponding points of said object in sal#
point sets of said two color channels of said at least two;
colour channels of said image, and
computing said displacement of said object as a distance
between corresponding points of said object in said point
sets of said two colour channels of said at least two
color channels of said image.
10. The method according to claim S, wherein said point
represents a centre of said object.
11. The method according to claim 8, wherein computing of,
said displacement for said object comprising portions of
at least two principle colours using said point~set
matching algorithm includes:
obtaining position information of portions of said object
in two colour channels of said at least two colour
channels of said image,
reducing said portions of said object in said two colour
channels of at least two colour channels of said image to
points to obtain point sets,
mapping the corresponding points of said portions of said
object i:i said point sets of said two color channels of
said at Least two colour channels of said image,
determining centers of said object in said two colour
channels of said at least two colour channels of said
image from said point sets representing said portions of
said object in said two color channels of said at least
two colour channels of said image, and.
computing said displacement of said object as a distance
between corresponding centers of said objects in said two:
colour channels of said at least two color channels ©f
said image.
12. The method according to claim 11, wherein said points
of said portions of said object represent centers of said
portions of said object.
13. The method according to any of the claims 9 and 11,
wherein the obtaining of position information of said
object if: each of the plurality of colour channels is
performed using a template matching algorithm.
14. The. method according to claim. 11, wherein the
determining of centers of said object in each of said at
least two colour channels of said image from said point
sets representing portions of said objects- in each of said
at least two colour channels of said image in said frame
is derived by offsetting from the points of the portions
of said objects.
15. The method according to claim. 5, wherein said velocity
of said c^bject is computed as a. ratio of said displacement
of said object, and a time difference of strobing light
sources a -sociated to the colour channels of said image,
16. The method according to claim 5, wherein said
accelerat ion of said object is computed as a ratio of
difference between a velocity (vtc) of said object during
its motion from a first colour channel to a second colour
channel and a velocity