Method and apparatus for surface effect characterization

Optics: measuring and testing – By polarized light examination – With light attenuation

Reexamination Certificate

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C356S446000, C356S236000

Reexamination Certificate

active

06226085

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to measuring the character or the appearance features of a surface and, more particularly, to a method and apparatus for characterizing and distinguishing color and surface effects using a spectrophotometer implemented with an integrating sphere.
BACKGROUND OF THE INVENTION
The measurement of the visual appearance of objects is of interest and of commercial value. Appearance is composed of several attributes of the object. The “color” generally is produced by the sub-surface diffuse reflection of light where colorants absorb different wavelengths to a varying degree, and is the primary attribute measured with traditional colorimetry instruments. Gloss is a surface appearance attribute, which is usually measured using a different instrument just for that purpose. Other surface characteristics or effects, such as surface undulations and roughness influence the viewed appearance of the specimen, which is not taken into account in normal instrumental color measurements and may in fact interfere with the desired measurement of the color and/or gloss.
Spectrophotometers for colorimetry are often equipped with an integrating sphere for the measurement of a specimen's reflection color. This standardized geometry often includes a means for controlling the specular (mirror like) reflection of the light from the sample. Often the instrument can measure the specimen with the specular component included (SCI) as well as excluded (SCE), which provides some information about the glossiness and smoothness of the specimen surface, but does not discriminate these effects.
U.S. Pat. No. 5,155,558 to Tannenbaum discloses a method and apparatus for analyzing surface appearance which depends on imaging a source aperture mask reflected from the sample, and analyzing the edge spread function of the reflected image of the mask. The image is received by a two dimensional CCD detector array. The edge spread function is interpreted using a Fourier transform to extract the spatial frequencies and associated amplitudes of the sample surface, in much the same way an optical surface or system is analyzed traditionally using the line spread function to reveal the Modulation Transform Function (MTF) of the aberration wavefront. More particularly, many CCD frames are captured while a mechanism scans through focus to optimize the sensitivity of the measurement for each of the various spatial frequencies of interest. A large amount of analysis on each frame is required to provide a line spread function from which surface appearance may be determined. Accordingly, although the method and apparatus of the '558 patent may provide accurate information about the sample surface, it analyzes surface effects only (i.e., it does not by itself also measure color), and it requires precisely controlled mechanical motion, multiple acquisitions, relatively large amounts of data, relatively slow measurement time, and relatively extensive data calculations.
There is a need, therefore, for further improvements in methods and apparatuses for measuring surface effects and/or surface appearance, and particularly, for measuring and distinguishing both color and appearance attributes of a specimen, preferably with a single measurement of the specimen.
SUMMARY OF THE INVENTION
The present invention, overcomes the above, and other, limitations of prior and background art spectrometers, by providing a method and system for implementing a new measurement modality for measuring surface characteristics or effects, as well as appearance, of a specimen. In accordance with an aspect of the present invention, a method and apparatus for characterizing surface effects of a specimen is provided for receiving at a receiver optical radiation reflected or scattered from a specimen, the optical radiation including specular components that are spatially encoded by wavelength according to chromatic aberration of the receiver (e.g., chromatic aberration of a lens or zone plate). A measure of surface characteristics is then provided by processing a signal representing the received optical radiation which includes the specular components that are spatially encoded by wavelength according to chromatic aberration.
The measure of surface characteristics may be a surface effect index representative of surface roughness and may be determined independently of calculating a function representing the spatial frequency content of the surface. In addition, the measure of surface characteristics may be a function representing the spatial frequency content of the surface, including functions thereof. An appearance measure, such as an indication of gloss/matte, “orange peel”, or gross flatness, may be calculated according to the function representing the spatial frequency content of the surface.
In accordance with another aspect of the present invention, an apparatus, such as an integrating sphere, includes a first receiver directed toward a specimen to receive first optical radiation reflected by the specimen. The first receiver has optics which provide chromatic aberration, and the first optical radiation received by the first receiver includes specular components that are spatially encoded by wavelength according to the chromatic aberration. The apparatus also includes a port or trap disposed substantially opposite to the first receiver such that a specular projection of the first optical radiation received by the first receiver overlaps the region contained by the port or trap. A processor processes a signal representing the first optical radiation received by the receiver to generate a measure of surface characteristics of the specimen based on the specular components that are spatially encoded by wavelength according to chromatic aberration.
In accordance with a further aspect of the present invention, both color and surface effects of a specimen can be characterized from a common measurement. Additionally, a plurality of receivers may be used in parallel. In accordance with an aspect of the present invention, a receiver and its corresponding port or trap may be configured to isolate sensitivity to spatial frequency content of the sample surface along predominantly one direction, and multiple such receivers may be used in parallel to concurrently distinguish effects or appearance attributes along different directions of the specimen. In addition, the receivers may be implemented in SCE mode or in SCI mode.
In accordance with yet another aspect of the present invention, a first receiver is directed toward a specimen to receive optical radiation reflected by the specimen, and a port or trap is disposed substantially opposite to the first receiver such that a specular projection of the optical radiation received by the first receiver overlaps the region contained by the port or trap. The size of the port or trap is adjusted to each of a plurality of sizes. For each of the plurality of port or trap sizes, the first receiver receives a corresponding optical radiation signal reflected or scattered from the specimen. A processor provides a measure of surface characteristics for the specimen based on the corresponding optical radiation signals.


REFERENCES:
patent: 5155558 (1992-10-01), Tannenbaum et al.
patent: 5182618 (1993-01-01), Heinonen
patent: 5384641 (1995-01-01), Imura
patent: 5661556 (1997-08-01), Schiff et al.
patent: 44 23 698 A1 (1996-04-01), None
patent: 0 335 192 (1989-10-01), None
patent: 4-115109 (1992-04-01), None

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