Patent Application
20050244078
This invention relates to photographic slides having specified transmission functions and to methods for making such slides. In certain embodiments, the specified transmission function is periodic.
One application of the invention is in the field of projection optical systems, and, in particular, projection optical systems used in three-dimensional imaging technology. In connection with this application, the photographic slides of the invention can be used to create desired light distribution patterns on a target plane or target object such as a patient's tooth.
U.S. patent Publication No. US 2003/0223083 entitled “Method and Apparatus for Generating Structural Pattern Illumination,” which was published on Dec. 4, 2003 and names Z. Jason Geng as inventor, discloses three-dimensional imaging methods in which patterns of colored lights are projected onto an object which is to be imaged. Various patterns are disclosed in this patent publication, including patterns in which the intensity of a projected colored light varies periodically across the surface of the object to be imaged. As shown in
The use of photographic film in optical systems which produce colored light patterns on an object is disclosed in Liu et al., “Color-coded projection grating method for shape measurement with a single exposure,” Applied Optics, 2000, 39:3504-3508, and Jeong et al., “Color grating projection moire with time-integral fringe capturing for high-speed 3-D imaging,” Optical Engineering, 2002, 41:1912-1917. However, neither of these references contain information as to the nature of the image recorded on the photographic film or whether the film conformed to specified transmission criteria.
The use of a linear variable wavelength filter (LVWF) formed on a glass plate to form three-dimensional images of objects is disclosed in Geng, Z. Jason, “Rainbow three-dimensional camera: new concept of high-speed three-dimensional vision systems,” Optical Engineering, 1996, 35:376-383. As described therein, the wavelength of light transmitted through the LVWF varies linearly with position along the filter, the linearity being better than 1% as measured by the filter's manufacturer (see page 379).
As discussed in U.S. patent Publication No. US 2003/0223083 referred to above, it is difficult to adjust the spectral variation rate of a LVWF to fit the accuracy requirements of many three-dimensional imaging tasks. As also acknowledged in this reference, the technology used to date to produce LVWF's have made such filters difficult and expensive to manufacture. In addition, due to manufacturing limitations, LVWF's have a relatively large footprint which make them difficult to incorporate in handheld devices.
Instead of a LVWF, three dimensional imaging systems that rely on the dispersion of an optical prism or a diffraction grating to produce illumination which varies spatially as a function of wavelength have also been disclosed. These approaches require expensive components and cannot be produced in a small envelope. They thus do not overcome the problems associated with the LVWF approach.
In accordance with a first aspect, the invention provides a method for producing a photographic slide using a computer screen having a plurality of pixels, said photographic slide comprising a user-specified type of photographic film (e.g., a user-specified type of positive or negative color film or a user-specified type of positive or negative black and white film) developed by a user-specified developing process (e.g., a commercially available developing process, such as, a developing process available to retail consumers, or a customized developing process, provided that in each case, the process is substantially identical each time it is used), said method comprising:
In certain embodiments of this aspect of the invention:
In certain embodiments, the final brightness pattern or patterns can be used to produce a plurality of photographic slides, e.g., the final brightness pattern(s) can be used in a manufacturing setting to produce photographic slides which are subsequently incorporated in 3D imaging systems.
As used herein, the phrase “user-specified” contemplates both specification prior to commencement of the method or at any point during the performance of the method, and includes changes to a specification during performance, e.g., changes to the user-specified criterion of step (F) after one or more iterations.
In accordance with a second aspect, the invention provides a photographic slide having a measured transmission function which:
In accordance with a third aspect, the invention provides a photographic slide having a red measured transmission function, a green measured transmission function, and a blue measured transmission function, each of which:
In connection with certain preferred embodiments of this aspect of the invention, the periods of the red, green, and blue measured transmission functions are (i) the same and (ii) are phase shifted relative to one another by one-third of a period.
In accordance with a fourth aspect, the invention provides a set of three photographic slides wherein:
In accordance with each of the foregoing aspects of the invention, the measured transmission function can have a triangular shape of the type shown in
Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention.
a illustrates the appearance of a periodic, triangular brightness distribution on a computer screen, and
a illustrates the transmission of a slide prepared by photographing the computer screen of
a illustrates the appearance of a periodic, non-linear brightness distribution on a computer screen, and
a, 7b, and 7b illustrate the transmission functions of three photographic slides of the invention where each of the transmission functions is triangular with the same period and the functions are offset from one another by one third of a period.
The foregoing drawings, which are incorporated in and constitute part of the specification, illustrate various embodiments of the invention. As with the written description, these drawings are explanatory only and should not be considered as restrictive of the invention.
As discussed above, the photographic slides of the present invention can be used in three-dimensional imaging systems and, in particular, in three-dimensional imaging systems in which desired light distribution patterns are formed on a target plane or object.
Systems of this type using a rainbow color pattern have been described in, for example, the Geng article in Optical Engineering discussed above. Sequential illumination with three spatial patterns of three different colors is described in U.S. patent Publication No. US 2003/0223083, also discussed above. Sequential illumination with a series of spatial light patterns having substantially the same spectral content is disclosed in U.S. application Ser. No. ______ entitled “Methods and Apparatus for Determining Three Dimensional Configurations”, Docket No. 58777US002, which is being filed simultaneously herewith. The contents of this co-pending application are incorporated herein by reference.
An optical layout suitable for use in producing a light pattern on a portion of an object whose three dimensional configuration is to be determined is shown in
To accurately determine three dimensional configurations using an optical system of the type shown in
In particular,
As can be seen in
Although the three colors are shown illuminating the object simultaneously in
Rather than using three slides to produce the intensity pattern of
The photographic slides of the invention can be prepared using an iterative technique wherein an image on a computer screen is photographed on film, the film is developed, the transmission function of the developed film is measured and compared with a desired transmission function, the image on the computer screen is modified based on the comparison, and the process is repeated as many times as necessary (e.g., 3-5 times) until the measured transmission function satisfies a user-specified criterion, e.g., substantial linearity. If the photographic slide is to contain more than one transmission function, e.g., a red transmission function, a green transmission function, and a blue transmission function, then the photographing, measuring, and image modifying steps can be performed separately for each of the desired transmission functions. If desired, only the measuring and image modifying steps can be performed separately with the exposing step being performed simultaneously for the various brightness patterns or a subset thereof. A display of multiple brightness patterns on a computer screen creates a complicated image. Displaying and exposing the film one brightness pattern at a time makes for simpler images and thus can facilitate a user's ability to follow changes to the brightness patterns as the process is iterated.
The slide preparation process can be performed entirely with commercially available products and processes, e.g., a standard computer monitor, standard photographic equipment suitable for photographing a computer screen, standard photographic film (color or black and white), and a commercially available development process, such as those available to retail consumers. In this way, photographic slides having desired transmission functions can be produced inexpensively, the cost being many times less than that involved in producing a LVWF. Of course, customized equipment and/or processes can be used in the practice of the invention if desired.
As just one example of the type of camera equipment and film which can be used in the practice of the invention, photographic slides having a high level of linearity (see
b shows the type of measured transmission function that results from photographing the brightness pattern of
c and 2d show the final screen brightness pattern and film transmission function achieved by iteratively adjusting the image on the screen until the measured transmission function is sufficiently close to the desired transmission function. As can be seen in these figures, the image displayed on the computer screen needs to be substantially different from a sinusoidal pattern in order to produce a transmission function which is sinusoidal.
The images on the computer screen which are photographed to produce the slides of the invention can be generated by controlling the color of individual pixels (individual dots) of the screen. The color of each pixel of a computer monitor is generally described as a RGB(AR, AG, AB) function, where AR, AG, and AB are integer numbers in the range from 0 to 255, with the intensity of each primary color being proportional to this integer. Equal values for AR, AG, and AB create different gray levels. The relationship between different colors and different RGB arguments is shown in Table 1.
If negative photographic film is used, additive colors for the RGB function can be used. Specifically, in this case, the brightness function for the pixels of the screen can be RGB(255-AR, 255-AG, 255-AB), where AR, AG, AB are the same arguments as in Table 1. When a brightness distribution of this type is photographed with negative color film, the developed negative slide (reversed color) will produce the desired color distribution on the target object.
Whichever brightness function is used, the light emitted by individual pixels is controlled using a software program with function calls capable of specifying RGB values for individual pixels. For example, the software program can be written in Borland's DELPHI language, where the command for assigning individual pixel colors and intensities is: Canvas.Pixels[m, n]:=RGB(AR, AG, AB), where m(n) is the row(column) of the pixel and AR,AG,AB are integer values between 0 and 255.
The program can, for example, scan across the pixels of the screen one row at a time specifying color/intensity values for each pixel. As is typical, the program will normally be designed to write and read color/intensity information from a memory file. The program can suppress the standard WINDOWS borders and caption area and can allow for variations in the number of periods per picture and the size and location of the pattern on the computer screen, including picture shifting within a window to achieve phase shifting.
Other approaches now known or subsequently developed for controlling the brightness distribution of a computer screen can be used in the practice of the invention as desired. As just one example, other programming languages besides DELPHI, such as C++, can be used to program a monitor to display a desired brightness pattern.
When black and white film is used, the brightness patterns on the computer screen can be generated by varying one and only one of the red, green, and blue values for the pixels of the screen. Similarly, for color film, the brightness patterns on the computer screen can be generated by varying one and only one of the red, green, and blue values for the pixels of the screen. Alternatively, in either case, the brightness patterns can be generated by varying red, green, and blue values for the pixels of the screen simultaneously.
As an example, the iterative adjustments to the brightness pattern can be made in accordance with an expression of the form:
In,m(k+1)=In,m(k)+Δn,m(In,m(k), tn,m(k), Tn,m) (1)
where:
Δn,m(In,m(k), tn,m(k), Tn,m) can, for example, be of the form:
Δn,m(In,m(k), tn,m(k), Tn,m)=(Tn,m/tn,m(k)−1)·In,m(k). (2)
The In,m(k+1) values can be normalized so that the maximum of those values equals the maximum brightness available for a pixel, e.g., the In,m(k+1) values can be normalized so that the minimum and maximum In,m(k+l) values after normalization are 0 and 255, respectively. Other values can be selected if desired.
The tn,m(k) values of these equations can be determined using various equipment known in the art for measuring transmission functions of photographic film. A suitable device is the MTF measurement system sold by Optics 1, Inc., 3050 E. Hillcrest Drive, Westlake Village, Calif. 91362, where light projected through a slide can be collected and analyzed to determine the slide's transmission function.
Equations (1) and/or (2), or equivalent equations, can be implemented using a software program which uses In,m(k), tn,m(k), and Tn,m as inputs and generates In,m(k+1) as an output. Such programs can be written in various programming languages known in the art and designed to run on, for example, a desktop computer.
a illustrates the transmission of a slide prepared by photographing the computer screen of
a illustrates the appearance on a computer screen of an adjusted brightness distribution obtained using equations (1) and (2) above, and
In particular,
The straight dashed lines of
As can be seen in
Linearity can be defined as the deviation of the measured intensity values from the linear approximations. An analysis of the data of
As discussed above, the period of the intensity function is approximately 106 linear units. Accordingly, for the linear zones, the transmission function of the slide is within 2 percent of a straight line (2/106×100=1.9%). As indicated above, the linear zones comprise more than 85 percent of a period. As also indicated above, substantially the same performance was observed for each of the periods making up the usable region of the slide. Accordingly, the slides of
Although specific embodiments of the invention have been described and illustrated, it is to be understood that a variety of modifications which do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the foregoing disclosure.
