Optics: measuring and testing – By shade or color – Trichromatic examination
Reexamination Certificate
2002-01-08
2004-03-09
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
By shade or color
Trichromatic examination
C250S23700G
Reexamination Certificate
active
06704108
ABSTRACT:
BACKGROUND OF THE INVENTION
A grating optical sensor is disclosed in WO 97/22 849. It is provided for accurately determining spatial and/or temporal spacings in focused image sequences of a lens/pupil system and/or determining spatial and/or temporal object parameters in real time such as, for example, speed or depth. A 3D grating has also already been used to carry out model calculations relating to the inverted retina of the human eye and to relate them to subjective phenomena known from human vision. In the preferred form, the 3D grating has a hexagonal structure. Other structures with centrosymmetrical diffraction patterns are, however, likewise possible.
Since the investigations of O. Lummer and the industrial development of daylight-like luminaires, it has been realized that there is an as yet unexplained resonance between sunlight and human vision. This has resulted in all the previous recommendations for approximating the spectrum of artificial light sources to the sunlight spectrum. In particular, in the case of color perception in phototopic day vision, there occur in the event of a change of illuminations having a different spectral composition of the radiation displacements of the color values which are compensated adaptively in human vision after a relatively short or, in part, relatively long time by means of approximate color constancy performances of the eye. The v. Kreis model, which attributes the adaptivity to the visual pigments of the retina, presently serves as an incomplete explanatory model for this. In addition, there are even more incomplete cortical explanatory models from other authors.
On the other hand, it has been documented many times that the phototopic seeing process cannot be characterized solely by the spectral light sensitivity of the individual cones. The very much more complex mode of operation of the visual sense requires knowledge of the luminance distribution in the entire visual field for the purpose of judging many visual tasks. Human vision is not based on the stimulus/reaction response of individual pixels. It takes account of the relative values over the entire field of view. In addition to chromatic adaptation effects, scattering of light at ocular media influences the extent of the achromatic axis (black-gray-white axis) centering the color space. It is therefore an illusion to believe that spectral photometers will be the ideal instruments of future chromatometry and color determinations, even if they are designed on the detection of overlapping RGB values. Likewise incomplete is a chromatometric technique which respectively dispenses with determining the triad of brightness/hue/saturation simultaneously and with reference to a entire field of view.
SUMMARY OF THE INVENTION
There is thus a growing need to have available in the future color sensors which can measure color values with reference to the spectral sensitivity curves of human vision, and ensure, given adaptation to artificial illuminations, an approximate color constancy corresponding to human vision. It is the object of the invention to create such a sensor.
The invention proceeds from the finding that it is possible, by inserting a diffractive multilayer (3D) grating into the image plane of an imaging lens/pupil system in the near field downstream of the grating (Fresnel/Talbot space; Fourier space or reciprocal grating), to make available three chromatic diffraction orders (RGB triple) with in each case six discrete interference maxima on mutually concentric circles, such as are described in the case of a hexagonal grating structure by means of the v. Laue equation known from crystal optics.
The v. Laue equation for diffractive space lattices requires for the production of constructive interference maxima the simultaneous satisfaction of the three phase conditions in the equation |1|
(cos&agr;-cos&agr;°)=
h
1
&lgr;/
gx
(cos&bgr;-cos&bgr;°)=
h
2
&lgr;/
gy
(cos&ggr;-cos&ggr;°)=
h
3
&lgr;/
gz
|1|
(h
1
h
2
h
3
=triple of integral diffraction orders n; &agr;°, &bgr;°, &ggr;°=aperture angle of the light cone incident in the 3D grating, relative to x, y, z; &agr;, &bgr;, &ggr;=angle of the diffraction orders relative to x, y, z; &lgr;=wavelength; and gx, gy, gz=grating constant in the x-, y-, z-axial direction). Assuming a hexagonal packing of the optically diffracting elements and grating constant dimensions in &mgr;m of gx=2&lgr;111, gy=4&lgr;111/3, gz=4&lgr;111, in equation |2|, &lgr;111 constitutes the wavelength diffracted with maximum transmission into the 111 diffraction order.
λ
h1h2h3
=
λ111
=
2
(
h1
gx
cos
α
*
+
h2
gy
cos
β
*
+
h3
gz
cos
γ
*
)
h1
2
gx
2
+
h2
2
gy
2
+
h3
2
gz
2
&LeftBracketingBar;
2
&RightBracketingBar;
In the case of perpendicular incidence of light (&agr;°=&bgr;°=90°, &lgr;=0°) a triple of chromatic diffraction orders results in the visible spectral region (380-780 nm)
&lgr;111 (longest wavelength) RED
&lgr;123 (average wavelength) GREEN
&lgr;122 (shorter wavelength) BLUE
The spectral transmission curves, which are centered relative to one of these &lgr;max in each case, have a Gaussian shape and are determined at their half width by the number of the surface gratings in the z direction that are present in the 3D grating. In the event of incidence of white light, that is to say light of identical energy in all spectral components, and the grating inserted into the image plane of the imaging system, given the selection of &lgr;111=559 nm, the result is the trichromatism of the diffraction orders at
&lgr;111 RED=559 nm
&lgr;123 GREEN=537 nm
&lgr;122 BLUE=447 nm
There is thus a trichromatic tuning of the 3D grating, which is based on the resonant setting of the grating constants gx and gz to an integral &lgr;111, and in which a trichromatic equilibrium of the brightness values (Patterson amplitudes
2
weights) is produced in the RGB diffraction orders.
In the case of adaptive chromatic retuning of the 3D grating to an illumination other than a white one, the relation of the RGB &lgr;max (1 : 0.96 : 0.8 or 25 : 24 : 20) is always maintained. &lgr;111 is the resonant wavelength determining the triple shifts to shorter &lgr;111 wavelengths in the event of change to a blue illumination, and to longer &lgr;111 wavelengths in the event of change to a red illumination. The adaptive shift ends with the complete adaptation to the new illumination, that is to say with the resonant finding of a new RGB equilibrium, of the trichromatically additive white standard, which recenters the color space. The actual resonance factor is the phase velocity nv&lgr;=c (n=refractive index of the medium, v=frequency of the light, c=speed of the light).
The following new configuration of the sensor design forms the basis for the color constancy performance of the 3D grating optical sensor in the case of adaptation to variable illuminations.
A diffusion plate or disc or glass (hereinafter “diffusion glass”) or one or more light diffusing gratings are incorporated into the pupil plane (aperture space) of the imaging optical system. Their function is to be seen in that they scatter diffusely as incoherent background into the image plane information likewise present at each location in the pupil, spatially the sum of the spectral intensities and local frequency values which are irradiated into the pupil by all objects in the object space and contribute to optical imaging. As a result, each local image location is supported by the global information on the entire field of view, against which each local pixel must stand out by being differentiated from it, specifically in brightness, hue, saturation etc. However, each item of local information thereby remains relativized in terms of the global background of the entire field of view.
All the lenses, diffusi
Foley & Lardner
Smith Zandra V.
Stock Gordon J
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