A method for measuring a contour of an object arranged on a reference plane by taking an image of the object formed on an imaging surface of a digital camera through a moire topographic optical system wherein a light source of a projector is disposed at the same height as a center of a lens of the digital camera relative to the reference plane, and the imaging surface of the digital camera and a grid plane of the projector having a one-dimensional equally spaced grid pattern of line segments, are arranged in parallel with the reference plane, wherein;
- in a coordinate system of the moire topographic optical system, an x-direction is defined as a direction extending orthogonal to each line segment of the grid pattern and a z-direction extending vertically to the reference plane, and a y-direction is defined as extending perpendicular to the x and z directions, and
- each element of pixel coordinate (i, j) of the image of the grid pattern projected on the imaging surface has a direction defined as extending in parallel to the x-direction and the y-direction, respectively,
- the method comprising;
- projecting the line segments of the grid pattern of the projector on the reference plane to form an image of the grid pattern on the reference plane,
- setting one period of the image on the reference plane so as to be reflected on the imaging surface as N pixels where N is an integer more than 2 and within the confine of the imaging surface,
- taking the image of the grid pattern projected on the reference plane by the camera to obtain a projected grid pattern image on the reference plane, and
- inputting the obtained projected grid pattern image on the reference plane into the computer,
- using a processor to obtain a phase distribution on the reference plane by a process effected in the processor of,
- extracting data of serial N pixels from the input projected image on the reference plane,
- obtaining a frequency spectrum of max power among frequency spectrums by processing the data of the serial N pixels through the discrete Fourier transformation to extract a frequency component of a period including N pixels of the frequency of 1 or −1,
- determining the phase of the extracted frequency component and storing thus determined phase corresponding to either pixel of the N pixels,
- shifting thus obtained an array of the N pixels by 1 pixel in the i direction and then carrying out the extracting, obtaining and determining repeatedly until reaching the confine of the imaging surface, and
- effecting the process including the extracting, obtaining, identifying and shifting in the j-direction to obtain the phase distribution of the projected grid pattern image on the reference plane,
- the method further comprising;
- projecting the line segments of the grid pattern of the projector on the surface of the object to form an image of the grid pattern on the object surface,
- setting one period of the image on the object surface so as to be reflected on the imaging surface as N pixels where N is an integer more than 2 and within the confine of the imaging surface,
- taking the image of the grid pattern projected on the object surface by the camera to obtain a projected grid pattern image on the object surface, and
- inputting the obtained projected grid pattern image on the object surface into the computer,
- using the processor to obtain a phase distribution on the object surface to be measured by a process performed in the processor by,
- extracting data of serial N pixels from the input projected image on the object surface,
- obtaining a frequency spectrum of max power among frequency spectrums by processing the data of the serial N pixels through the discrete Fourier transformation to extract a frequency component of a period including N pixels of the frequency of 1 or −1,
- determining the phase of the extracted frequency component and storing thus determined phase corresponding to either pixel of the N pixels,
- shifting thus obtained an array of the N pixels by 1 pixel in the i direction and then carrying out the extracting, obtaining and determining repeatedly before reaching the confine of the imaging surface, and
- effecting the process including the extracting, obtaining, determining and shifting in the j-direction to obtain the phase distribution of the projected grid pattern image on the object surface,
- the method further comprising
- connecting thus obtained phase distribution on the reference plane and that on the object surface wherein:
- moire fringes, defined as a difference between the phase on the object surface and that on the reference plane, are obtained on each pixel of the camera, and
- the contour of the surface of the object is obtained by processing the phase of the obtained moire fringes.