Application of Colour Rulings in

Shadow Moiré Technique

Paveleva Daria,

Dr. Wenzel Klára,

Antal Akos

Lux et Color Vespremiensis

2007. October 2007 19, Veszprém

Budapest University of Technology and Economics Department of Mechatronics, Optics and Engineering Informatics

Moiré phenomenon

The French word "moiré" is

usually used for the name of the

silk fabric which has changing

undulating pattern.

The phenomenon of moiré fringes

was first described by Lord

Rayleigh in 1874.

Moiré phenomenon is seen

wherever a repetitive structure is

overlaid with another structure

and the line elements are nearly

superimposed.

Application of moiré phenomenon

1. Measuring of components, moulds and tools in deformation technologies Cast industry

Forging industry

Tool making and mould design

Sheet metal industry

Structure deformation under thermal or mechanical loading

Contour inspection of manufactured parts in the production process

Vibrations studying

Road deformation

2. Measuring of human body in medicine and dentistry Plastic surgery, e.g. manufacturing of individual prostheses

Measurement of spinal curvature

Manufacturing of dental prostheses (inlays, crowns, bridges etc.)

Moiré measurement technique

Shadow moiré method uses a

single grating placed in front of the

object, that produces a shadow on

the object which is viewed from a

different direction through the

grating.

Projection moiré method uses two different

gratings for observation of the moiré patterns.

Computer aided method is not a pure optical

method, as for generation of moiré patterns

synthetic grating is used like a reference

grating.

The problem of “hills&valleys” in

moiré images

As it is common for most measurement techniques, moiré technique also

has inherent characteristics that allow or limit its use in certain types of

applications.

Measuring object Moiré image

The concave and convex regions of measuring object cannot be distinguished

from the one moiré pattern

Hill?

Valley??

Hill?

Valley??

Moiré method

Problem solution by application of colour rulings in gratings

For obtaining extra information the phenomenon should be changed to the

asymmetrical, for example, by means of two-colored grating application.

Colour moiré gratings

Concave and convex surfaces by application of colour moiré effect

The variants of colour moiré fringe

formation

Colour difference between the two areas in the effective moire fringe should be

Superposition of one colour and

one Ronchi grating

Superposition of two colour gratings

with the opposite order of color bars

Superposition of two colour gratings

with the same order of color bars

Projection

method

Shadow

method

Experimental results

Combination of red and blue

colour bars was chosen by

most participants of the

experiment

Combinationof the two

colour gratings was

preffered to the black and

colour one

Selection of the most “

effective” moiré effect –

BL&COL, “ineffective” –

COL&COL (op.) – that

corresponds to the shadow

moiré method

30 subjects participated in the serie of the experiments. 6 gratings with combination

of colour bars: RB, G-R, B-G, C-M, Y-C, M-Y and the traditional black-white grid were

made.

The answer to the problem of “ineffective” colour moire appearance

in shadow technique

The color formation principle by the

superposition of two color gratings (a)

and one color grating with the black-

white grid (b). The letters correspond to

the variants of color appearance as a

result of gratings’ superposition

Colour transformation in the ready shadow moiré image :

1. Change the master grating to the black one

2. Change the order of color bars in the master grating

The original colour

shadow moiré

without additional

information (a), the

image that is

modified to colour

and colour type with

opposite order of

rulings (b), and the

image modified to

black-white type (b)

Experimental results

THANK YOU FOR YOUR ATTENTION!!!