Electronic processing of moiré fringes: application to moiré topography and comparison with photogrammetry

Application of automatized 3D moiré monitoring system in pulse measurement

This paper presents a quick monitor method to measure micro height variations directly. Here we apply optical moiré technology with a program designed by ourselves to Traditional Chinese Medical Pulse diagnosis. We analyze the moiré pattern which records the information of pulse, and then examine the conditions of pulse, the conditions of pulse including the location of pulse (by image processing the moiré pattern), the rhythm of pulse (via the frequency), the shape of pulse (via moiré pattern) and the strength of pulse (via amplitude intensity). Therefore, we can quantify the conditions of pulse by the system.

Quantitative measurement of volume changes induced by oral plastic surgery: validation of an optical method using different geometrically-formed specimens

The purpose of this research was to study the validity and variability of a projection Moiré system, measuring volume differences of geometrically different formed specimens mimicking localized alveolar ridge defects. Nine pairs of specimens were fabricated, each of which simulated a preoperative ridge defect and a corresponding surgically-corrected postoperative ridge defect. All specimen pairs had a mathematically defined form which allowed the accurate assessment of their volume differences by a mechanical 3-D coordinate measuring machine or by a software-controlled milling machine. Measurements achieved with these methods were used as the references for comparison. Six specimen pairs, A1 to A6, possessed a simple rectangular geometrical form which facilitated their fabrication. Three specimen pairs, B1 to B3, were milled and consisted of geometrically more complex 3-D sculptured surfaces, which came closest to a true imitation of a localized ridge defect. An optical measurement system in the form of the projection Moiré was utilized, applying a 4-phase shift technique, and results obtained with this device were regarded as test volumes. The absolute variability of the test volume measurements differed between 0.397 mm3 to 15.872 mm3, corresponding to a relative variability of 0.83% to 2.83%. The mean of the relative variability was within 1.68% for the "A" specimens and 2.15% for the "B" specimens. However, the difference was not significant, probably due to the limited number of "B" specimens. The systematic error of the Moiré measurements in relation to the reference methods was surprisingly low, ranging from -0.12 mm3 to 7.67 mm3. The relative systematic error, expressed as a percentage of reference volume, ranged between 0.06% and -2.23%. The mean of the relative error for the more complex "B" specimens was 1.37%, which was less accurate in comparison to the more simply formed "A" specimens with a relative systematic error of 0.35%. Therefore, in this in vitro model it was possible to measure volume differences of geometrically different formed specimens, mimicking localized alveolar ridge defects, with a validity within 2.2% and with a variability of less than 2.8%.

Automatic shadow moiré topography: a moving-light-source method

A method for automatically determining in real time the absolute order of shadow moiré fringes is developed. The intensity variations on an object surface caused by a light source moving with constant speed are analyzed by fast-Fourier-transform methods. Experimental results show that this procedure can be successfully applied to shadow moiré topography and does not require object surface continuity.

Optical methods to measure shape and size

A number of methods are available to quantify exterior size and shape of living and non-living objects. Relevant items for dentistry are the exterior of face and skull and the surface of dental casts. To the best of our knowledge, dentitions have not yet been measured in situ. The optical methods using incoherent light are mechanical sensing of casts, visual stereometry (on the subject or on stereophotographic pairs), moire techniques, and optical-sensor morphometry. It will be shown that the three latter systems in fact rely on the same physical principles, although they involve quite different technologies. On the other hand, coherent optical techniques, such as holography and contouring holographic interferometry, are presented.

The basic principles of the different techniques are shown, and their main features in relation to applications to the dental object discussed. Main features include: resolving power, range, time needed for a measurement, requirements for the surface of the object, and ease of selection and collection of data. Examples of methods from the literature and from work by the author are given.

Magnified grating images used in displacement sensing

Highly magnified images of a periodic object placed in the close vicinity of the rectangular grating have been obtained by incoherent illumination. The imaging behavior has been explained quantitatively on the basis of the optical transfer function of the system. By advantageously using the high magnification involved, this phenomenon has been discussed for the purpose of precise displacement measurements. Furthermore, an explanation of Lau imaging has also been included as a spatial case of the phenomenon under consideration.

Electronic heterodyne readout of fringes in moiré deflectometry

An electronic heterodyne technique is described for the readout of fringes in moiré deflectometry. The technique is based on phase measurements of signals generated by a photodetector observing the light transmitted through a traveling moiré fringe pattern. The phase of the signal is proportional to the fringe deviation and thus to the deflection angle of the light ray. The phase is measured on line by a standard phase meter with an accuracy of 1 degrees or 1:360 of a fringe. The technique, which is precise and sensitive, is demonstrated by detecting and measuring a fringe shift of 0.15 mm corresponding to 0.029 of a fringe.

Moiré topography, sampling theory, and charged-coupled devices

Projection-type moiré contouring can be done without a reference grid by undersampling projected cosine fringes with a charged-coupled-device detector array to eliminate entirely the unwanted sum, shadow, and grid terms of classical moiré methods as well as the spurious moiré fringes that are due to higher harmonics. The technique produces a high-visibility sampled version of the moiré difference contour fringes. Higher-order aliasing can provide increased sensitivity when the same detector array is used. The sampling conditions are formulated as a moiré extension to the Whittaker-Shannon sampling theorem.