MORPHING-BASED VECTORIZED CANDLE ANIMATION FOR

LASER GRAPHICS

PURKHET Abderyim , MENENDEZ Francisco. J, HALABI Osama,CHIBA Norishige

Department of Computer Science Graduate School of Engineering Iwate University

E-mail: purkhet@cis.iwate-u.ac.jp , fcomenendez@cg.cis.iwate-u.ac.jp, {ohalabi,nchiba }@cis.iwate-u.ac.jp

ABSTRACT

Raster and vector are two common forms of graphics

display systems. In this paper we introduce a new approach

to display vector graphics by using a laser projector. The

laser beam does not diffuse nor lose intensity over distance.

These characteristics make laser projection suitable for

large scale graphics. Laser projector is different from

vector-based display in a way that it has its own properties

such as the speed of laser beam and inertia of the reflective

mirror. In this paper we present a method for creating

vector data from an image and projecting using laser

projector. The process starts by first extracting the binary

image of the raster image and find contours then obtaining

polygonal approximation of raster shape. Through this

process, we converted a raster image according to the

levels of its grey scale to a vector image that can be

displayed using a laser projector. A Morphing technique is

also proposed to create laser animation from a single

candle vector data. A recursive vector subdivision

algorithm is used to achieve smoother result.

1. INTRODUCTION

In the early 1960s graphic display devices were developed

which were called vector or calligraphic. A vector graphics

display is basically a computer controlled oscilloscope. It

draws lines and curves by moving the electron beam

exactly where the line is supposed to go. To draw a line

from point a to point b, it moves the electron beam to point

a, turns it on, moves it directly to point b, and turns it off.

They draw line segments as their primitive display

operation [1]. Because of disadvantages such as the

difficulty to avoid flickering and color capabilities, vector

displays were replaced by raster displays which display

graphics by arranged vertical and horizontal pixels.

Although raster displays can resize their image as they are

moved away from the screen, there is a limit on how much

this resizing can happen. Beyond a certain point, the pixels

being to blur out and lose quality. Furthermore, raster

projectors should be displayed in special screens.

Otherwise, the colors and intensity will fade. With laser

projectors, these two problems do not occur. Laser

projectors are using two fast moving mirrors that create the

illusion of lines and shapes. Because of fast mirrors inertia

laser project can create more smooth graphics than vector

display.

The laser beam has three properties that make it suitable

for a large scale graphics. First, the light is monochromatic,

or one pure color (although some lasers emit more than one

color, each is pure, not muddy). Second, laser light is

collimated, meaning that it does not spread out and diffuse

like other types of light (such as incandescent). Third, the

laser beam does not lose intensity over distance [2].

Lasers have been used in the entertainment especially in

laser shows. There are two categories of the laser effect.

One is Beam Effects − show the laser beam that

progressing in the air to the audience, the other is Screen

Effects − show the laser graphics on the screen that drawn

in moving a laser spot on the screen. However there is little

or none previous research done on laser graphics, therefore,

it is worth to explore many problems and application that is

inherented to laser projection displays.

In this paper we use a laser projector [3][4] to draw

graphics objects. Since the projector only understands

vector data, the algorithms we need are different from

those used in nowadays raster display devices. We use line

segments as primitive display operation instead of pixels.

Smooth candle animation for laser graphics was created by

using vectorization and laser graphics techniques. First

convert raster image to get vertices, generate vectors and

project them using a laser projector. Second, using a raster

grayscale image, we obtain vector information to be

displayed by the projector. Also, we adapt one raster

morphing technique so it can be used with vector graphics.

1.1 Previous Work

Vector and raster are the two major approaches to create

graphics. A vector device draws lines to create whole

graphics, while a raster device uses an array of closely

spaced dots to form a picture. Early computer graphics

works on vector device such as “Tektronix 4010”. Basic

graphics concept were introduced based on vector graphics

[7] such as clipping and viewports, etc. The famous video

game “Asteroids” utilized a monochrome vector graphics

display, which was capable of fast moving objects made of

very sharp lines Combined with great game play it became

the biggest selling of game of its time. Vector display offers

high resolution and allow varying levels of intensity [8].

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The advantage of vector graphics is that lines and curves

look much cleaner than their rasterized equivalent. They

suffer much less from "aliasing", or "stepping" which is a

result of breaking a diagonal line up into dots, resulting in

something that looks like a staircase in some cases.

Because the electron beam actually moves diagonally from

the beginning of the line to the end, the resulting line has

very straight, clean, diagonal edges.

Formally, there is little or no previous research done on

laser graphics. However, there has been a big amount of

work done. In industry, laser cutting is used to cut metals

and other materials. Lasers have been used for marking

products in a production line. A printing laser is used to

mark things such as lot and serial numbers, as well as

manufacturing and expire dates [12][6]. In medicine, the

laser scalpel is used for laser vision correction and other

surgical techniques. In the music field, lasers have been

used for a while as part of laser shows in dance clubs [2]

and laser hobbyists. Yet these shows usually employ very

simple, static animations (they do not change once they

started and repeat endlessly) or the lasers simply move to

match the rhythm of the music playing.

There is also an association called ILDA [9] (International

Laser Display Association), which is the world's leading

organization dedicated to advancing the use of laser

displays in the fields of art, entertainment and education.

It has shown some efforts into moving towards a standard

file format and hardware specifications, these standards

have a commercial goal only, as they benefit the exchange

of products and services.

2. EXPERIMENTAL LASER

PROJECTOR

A laser projector can be built in many ways. The most

common way to control the laser beam is by rotating

mirrors with its corresponding galvanometers. The basic

components of our laser projecting system consist of the

following:

Scan controller : It is responsible for communicating

with PC and axis servos, and it is has some memory to

store programs before sending them to the axis servos.

Axis servos controller: It converts the digital signals from

the main controller into analog currents for the

galvanometers and also communicates the position

feedback to the scan controller.

Power: supply power to laser projector.

Galvanometers and mirrors: galvanometers turn mirrors

to control the x and y direction of laser beam.

Laser beam: A laser beam of a given color and intensity.

The operation of the projector is achieved by sending

instructions into the controller. These instructions are sent

to the corresponding servo controllers that rotate the X and

Y mirrors by changing the current on the galvanometers.

The laser beam stays static and it is the reflection on these

two fast moving mirrors that creates the illusion of lines

and shapes on the projection screen.

The projector used in our experiments was built using the

following components: [3][5][6]

Scan Controller: GSI Lumonics SC2000

Servo Controllers: GSI Lumonics MiniSAX (2 units)

Galvanometers: GSI Lumonics VM-500

Laser: Coherent MVP Control Diode Laser Module.

Wavelength: 670nm±10nm (Red). Power: 0.95mW

3. LASER GRAPHICS RELATED ISSUES

In constant laser beam intensity, if two lines of different

length drawn in the same interval, the shorter line will look

brighter than the longer one. Because in same time interval

drawing longer line, laser projector moves mirror faster

than drawing shorter one. The slower the mirrors move the

brighter laser beam line come into sight (in Figure 2 a).

Laser projectors have the ability to control not only the

coordinates from and to the laser beam should move, but

also the time in which this movement happens.

Constant brightness can be achieved either by moving the

(b) Same brightness

(a) Different brightness

Figure 2: Mirrors’ speed effects Power

Axis servos controler

Scan Controller Laser beam

Galvanometer

s and mirrors

Figure 1: Laser Projector

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(a) (b)

(c) (d)

Figure 3: Inertia effects

laser beam with a constant velocity for all vectors by

adjusting beam intensity for different vectors, or by

constant laser beam intensity with adjusting moving speed.

In this paper we calculate the moving speed according to

the length of the lines which will be drawn. In this way, all

the drawn lines have the same brightness (Figure 2 (b)).

Laser projector is different from vector display in the way

they display a line segment. Laser projector presents line

segments by controlling two mirrors, one for X and another

for Y dirction.. When the mirrors try to quickly switch

from one position to the next, the mirrors inertia effect will

appear, which produces a curved effect on straight corners.

This enables us to represent smooth curves with less line

segments. For example, to represent the circle shown in

Figure 3 (a) with line segments, we used same numbers of

line segments (Octagon) but with different moving speed

(different inertia ) as can be seen in Figure 3 (b)( c), and

(d) , In Figure 3(b) the shape represents a polygon rather

than a circle, moving speed is 10 frame per second (fps).

Curved effect appeared on the angle points in Figure 3(c)

when 40 fps was set. In Figure 3(d) we redraw the shape

with 100 fps, and the inertia influence could be clearly

observed as the octagon become more and more rounded

and closer to circle.

4. CANDLE ANIMATIONS

In contrast to raster graphics, where images are represented

by a two-dimensional array of pixels, laser projectors are

vector based devices. This means that objects can only be

represented using straight line segments between

addressable points.

4.1 Vectorization

Since laser projectors are vector-based displays, they

perform best when the drawing is composed of only one

contour and the laser does not need to be turned on and off.

Having this in mind, we convert the raster image to a

vector image using Contour Retrieving techniques.

To achieve this, we first binarize the raster image, find its

contours and store them in the chain format for polygonal

approximation of the chains [10]. From the obtained

polygon vertices, we generate vectors and project them

using the laser projector. In this way, we avoid to turn the

laser beam off and on that is to achieve less flickering.

To demonstrate our vectorization method, we carried out

experiments with various objects from images with

different complexity. Figure 4 shows the process of

processing a raster image to get vertices, then generating

vectors and projecting them using a laser projector. The

entire raster image consists of three objects which are

represented by three single line graphs. The circle object

was vectorized as a polygon because in laser graphics

curves have to be represented by a group of line segments.

Vectorization algorithms only find contours in the binary

raster images. In order to display grayscale images with

lasers we can convert the original image into a set of binary

images by using different thresholds, and later apply

Contour Retrieving techniques described before to each

image of in the set.

Original raster image

Approximate polygon

Laser image

Figure 4: Laser drawing process

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Figure 5: Contour for different grayscale

original image contours laser image

To create the feeling of grayscale using lasers, we must

change the intensity of the beam for each contour. To

achieve this, we calculate the moving speed not only

according to the length, but also based-on grayscale level

of each contour (Figure 5).

In Figure5 instead of obtaining one single polygon we get

several polygon depend on the grayscale level of the image.

The candle flame can be represented by several individual

single line graphs. Also each curve brightness was

calculated according to it is grayscale value. Since we

cannot define a single edge for the candle flame,

vectorization occurred on different grayscale levels. In this

example we use three different grayscale level thresholds

(50, 128, and 250) respectively.

4.2 Vector morphing

Morphing is an image processing technique used to

smoothly change one image into another. The idea is to get

a sequence of intermediate images which, when put

together with the original images, would show the

transformation. The simplest method of converting one

image into another is to cross-dissolve between them. In

this paper we used the feature-based image metamorphosis

[11] to create new vector data animation from original

vector data that obtained from the raster image. We then

use noise to move the control line in order to generate the

destination image.

In image morphing, each pixel in the source image is

mapped to an appropriate place in the destination image.

However, since in laser graphics, segments are the

primitive operation, instead of applying morphing for

every pixel, we only transfer vertices.

After we get vector data using vectorization, we apply

feature-based image metamorphosis to obtain new vector

data.

Because we apply morphing only to the starting and ending

vertices of the line segments, we lose some smoothness of

the generated image. For example, using the morphing

method on a vertical line in raster mode with three

horizontal control lines, the straight line becomes smooth

curve after the transformation (Figure 6, left). However, in

laser morphing line remains straight after the

transformation. This occurs because in laser morphing only

start and end points are moved, resulting in loss of

accuracy.

To solve this problem, we subdivide the original vector into

smaller vectors, depending on the resulting morphed

coordinates. Figure 7 shows how to accomplish this task.

We first subdivide vector at the midpoint (O) and calculate

it is morphed position (O1), if O1 is not on (or near to) P1Q1,

we divide the vector PQ into two vectors then apply

morphing process again.

The algorithm steps are as following:

Step 1. From vector PQ and its middle point O calculate

morphed points P1 ,Q1 and O1.

Step 2. Calculate angle P1 O1Q1

Step 3. If the angle is smaller then threshold angle

Insert O1 to vertexes list and replace P1Q1 with

O1P1 and O1Q1 respectively then go to step 1. If

the angle is bigger than a threshold then finish

subdivision.

In Figure 5 vector PQ became 3 subdivided vector.

5 RESULTS

We were able create a candle animation with our laser

projector from a raster image. To create the feeling of

grayscale using lasers, we changed the intensity of the

beam for each contour. To achieve this, we calculated the

Raster morphing Laser morphing

Control line

Original line

After morphing

Figure 6: Smoothness problem of vector

O

Q

P

Figure 7: Subdivision in Laser Morphing

P1O1Q1 angle

P1

Q1

O1

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Figure: 8

original without subdivision with subdivision

moving speed not only according to the length, but also

based on the grayscale level for each contour. To solve this

problem, we subdivided the original vector into smaller

vectors, depending on the resulting morphed coordinates.

Figure 8 is an example of the laser morphing processing

feature. Both edges of rectangle were subdivided and the

number of vectors increased after morphing.

Figure 9 shows the animation frames of the candle

animation displayed using our laser projector. Each picture

was every 10 steps. We can clearly distinguish the

continuity of the candle animation. Vectorization process

was employed only once to obtain the original shape. From

this vector data, the rest of the animation was created by

changing the position of the vertices. This change depends

on morphing produced by applying noise to the control

line.

4. CONCLUSIONS AND FUTURE WORK

In this paper we introduced the laser graphics for

displaying computer graphics using a laser projector and

implemented some basic application such as converting

raster image to vector image that can be displayed using a

laser projector and laser morphing.

As for the future work, there is a lot of areas that this

research can be further extended. After converting raster

image to vector laser graphics we can use it for cartoon

drawing. By using grayscale information with laser power

density it is possible to research on non-photorealistic

rendering with laser projector.

ACKNOWLEDGEMENTS

We would like to thank Mr. Norihiro Nasukawa for his

valuable technical support by building and maintaining the

laser projection hardware.

REFERENCES

[1] Eugene L. Fiume. the Mathematical structure of raster

graphics. Academic Press (1989). ISBN: 0122579607

[2] Laser Light Shows and Laser Displays:

http://www.laserspectacles.com/pages/liteshow.htm

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MENENDEZ Francisco, HALABI Osama, CHIBA

Norishige, 1E-04, Development of Experimental Laser

Projector, Tohoku-Section Joint Convention of

Institutes of Electrical and Information Engineers 2006,

(in Japanese)

[4] MENENDEZ Francisco, ABDERYIM Purkhat,

NASUKAWA Norihiro, HALABI Osama,

CHIBA Norishige. 2A-16 Research Towards Laser

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Convention of Institutes of Electrical and Information

Engineers 2006.

[5] GSI Lumonics. Optical Scanners and Controllers:

http://www.gsig.com/

[6] Coherent Lasers: http://www.coherent.com/

[7] FOLEY J.D., VAN DAM A. Fundamentals of

Interactive Computer Graphics. Addison-Wesley (1982).

ISBN: 0201144689

[8] DENNIS Harris. Computer Graphics and applications.

Chapman and Hall(1984). ISBN: 0412250802

[9] International Laser Display Association (ILDA):

http://www.ilda.wa.org/

[10] OpenCV Reference Manuals

http://vision.cis.udel.edu/opencv/

[11] T. Beier and S. Neely. Feature-Based Image

Metamorphosis. Computer Graphics (SIGGRAPH '92),

pp. 35-42, July 1992.

[12] Epilog Laser: http://www.epiloglaser.com/

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Figure 9 : The frames of the candle animation using laser projector

The step number is shown between parenthesis

(0) (10) (20) (30) (40) (50) (60) (70)

(80) (90) (100) (110) (120) (130) (140) (150)

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