Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2001-01-03
2004-02-10
Fuller, Rodney (Department: 2851)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C356S303000, C356S319000
Reexamination Certificate
active
06690465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus which are suitable for use in measuring a spectral irradiance distribution.
2. Description of the Related Art
When a computer, such as a personal computer (PC, hereinafter also called the computer) processes a color image, such as editing a color image captured into the computer using a scanner while checking the color image displayed on the monitor, or printing a color image using a color printer, colors of an object for processing have to be accurately calculated by the computer.
Generally, the basic colors of an object are expressed in the form of tristimulas XYZ values of the light reflected from the object (Günter Wyszecki and W. S. Stiles, “Color Science: Concepts and Methods, Quantitative Data and Formulae Second Edition, 3.3.8 Calculation of CIE Tristimulus Values and Chromaticity Coordinates”, John Wiley & Sons, Inc. (1982)). Accurate calculation of tristimulas XYZ values requires the spectral irradiance distribution of light irradiating the object.
A spectral irradiation distribution is a physical value indispensable for accurate processing of a color image. For example, tristimulas XYZ values are essential factors to estimate a print image to be printed by the printing machine.
The conventional method of measuring a spectral irradiance of the light irradiating a particular surface is exemplified by a method of dividing into spectral distributions by a spectral filter, and measuring the respective spectral irradiance distributions of the individual spectral distributions by a plurality of photosensitive sensors in accordance with various wavelengths of the spectral distributions. This spectral irradiance distribution measurement is performed by a dedicated apparatus.
However, such conventional apparatus has to be equipped with these photosensitive sensors having different optical sensitivities as many as the number of the wavelengths by which the measurement is performed. As a result, the conventional apparatus is complicated and very expensive due to the increased number of the photosensitive sensors.
As spectral irradiance distribution measuring method using photosensitive sensors whose number is less than that of the measuring bands are disclosed in (1) Shoji Tominaga, “Multichannel Vision System for Estimating Surface and Illumination Functions”, J. Opt. Soc. Am. A, Vol. 13, No. 11, 2163-2173 (November 1996), in which a spectral irradiance distribution of the light irradiating an object is measured as shown in
FIG. 9
, and (2) Japanese Laid-Open (Kokai) Publication No. HEI 11-132853, in which a spectral irradiance distribution of a light source is directly measured as shown in FIG.
10
.
These two conventional methods will now be described more with reference to
FIGS. 9 and 10
.
(1) Method of measuring a spectral irradiance distribution of light irradiating an object:
With this conventional method of
FIG. 9
, the spectral irradiance distribution of the light irradiates an object
183
(irradiating light), whose spectral reflectance is not given, from a light source
180
and the spectral reflectance are calculated. At that time, the object
183
is photographed by a 6-band camera
182
, which has sensitivity to 6 colors of RGB colors (red, green, blue) and to the other three colors, and then the spectral irradiance distribution of the irradiating light and spectral reflectance of the object
183
are measured based on the photographed image.
Since unknown coefficients and numbers upon the measurement are many, special equipment called the 6-band camera
182
is used. Further, the measurable spectral irradiation distribution of irradiating light is limited to such range so as to expressed by a linear combination of three components.
(2) Method of measuring a spectral irradiance distribution of a light source directly:
In this conventional apparatus of
FIG. 10
, plural optical filters
281
respectively having different spectral transmittances are individually disposed on the irradiating path of a light source
280
emitting light to measure emitting light thereof. The plural sensors
282
respectively installed in accordance with the individual optical filters
281
so as to receive the light transmitted through the optical filters
281
. As a result, a spectral irradiance distribution of the light is estimated referring to the spectral transmittances of the optical filters
281
.
Subsequently, outputs from the optical sensors
282
are converted into voltage values by an amplifier and then are further converted into digital data by an A/D converter to calculate the spectral irradiance distribution and chromatic characteristic the light source
280
in terms of the digital data on a computer.
However, the above-mentioned conventional methods have the following problems:
One method of
FIG. 9
requires special equipment of 6-band camera, and a measurable spectral irradiation distribution of irradiating light is limited to such a range so as to be expressed by a linear combination of three components. Generally, indoor light sources are various types, many of which are complicated. Therefore it is practically difficult that all types of indoor light sources are measured under the same restriction that a spectral irradiation distribution is measured within a range such as to be expressed by a linear combination of three components.
In the other method of
FIG. 10
, the spectral irradiance distribution of the light source
280
is directly measured. It is impossible to measure the spectral irradiance distribution of the light irradiating an object surface. And there is a significant restriction that a spectral irradiance distribution of only light sources very similar in spectral irradiance distribution to a single predetermined light source.
Accordingly, with either these two conventional methods, it is difficult to measure a spectral irradiance distribution of light irradiating an object surface without using any expensive measuring equipment.
SUMMARY OF THE INVENTION
With the foregoing problems in view, it is an object of the present invention to provide a method of measuring a spectral irradiance distribution of light irradiating an object surface without using expensive measuring equipment. Another object of the invention is to provide an apparatus for carrying out the above-mentioned method.
In order to attain the above first-named object, according to a first generic feature of the present invention, there is provided a method of measuring a spectral irradiance distribution of light, comprising the steps of: receiving the light on s (natural number) optical sensors, which respectively have s kinds of given spectral sensitivities, via n (natural number) light-transit sections, which respectively have n kinds of given optical characteristic coefficients; detecting individual responses for the light (receiving irradiances of the light), which is received via the n light-transit sections, by each and every one of the s optical sensors, and obtaining (n×s) responses for the received light; and calculating m (natural number) spectral irradiances for m kinds of wavelengths as a spectral irradiance distribution of the light, based on one or more linear formulae established between the optical characteristic coefficients, the spectral sensitivities, the (n×s) receiving irradiances, and the spectral irradiance distribution of the light. With this method, it is possible to calculate a spectral irradiance distribution of light with ease and to make the apparatus simple in construction with the reduced number of the optical sensors.
As a preferable feature, the optical sensors and the light-transit sections are arranged in such a manner that the number (n×s) of the responses for the light detected by the optical sensors is equal to or larger than the number (m) of the spectral irradiances to be calculated based on the linear formulae; and the m spectral irradiances are calculated by directly solving the linear formulae. With this preferable
Mori Masahiro
Shimizu Masayoshi
Suzuki Shoji
Armstrong, Kratz, Quintos Hanson & Brooks, LLP.
Fujitsu Limited
Fuller Rodney
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