Method and apparatus for recording stereoscopic images on precoated lenticular material

Abstract: A method and apparatus for printing three dimensional pictures includes imposing lines of information in the form of segmented images of a scene onto a light sensitive material. Alternate segments or lines are provided from different perspective views of the same scene to be printed. The light sensitive material has a transparent lenticular material attached thereto. The light sensitive material is exposed, from the side opposite the lenticular material, by light from an illuminated image. The exposure may be effected by optical projection or by contact printing or by CRT image projection or other means. A reference grid, having a pitch slightly different from the pitch of the lenticular material, is positioned on the lenticular material and is effective to cause a Moiré pattern to become visible when the lenticular material is moved relative to the light sensitive material. The Moiré pattern is used to adjust the position of the lenticular material or the negative, prior to exposure of the light sensitive material. After exposure, a reflective material is applied to the side of the light sensitive material opposite the side to which the lenticular material is attached, to provide a three dimensional print. In another example, several reference grids are used for additional accuracy of alignment.

Description: FIELD OF THE INVENTION The present invention relates generally to image reproduction and more particularly to an improved method and system for producing three-dimensional pictures. BACKGROUND OF THE INVENTION There are two general methods of recording lenticular sheet three-dimensional pictures, viz, continuous methods and discontinuous methods. In a continuous method, the lenticular sheet with a photosensitive image layer affixed or clamped to the back surface is placed in a camera used to capture the image. In taking a three-dimensional picture, images of the object observed from various directions are recorded directly and continuously on the photographic plate. In a discontinuous method, a series of planar images representing different perspective views of a scene are obtained first, and they are synthesized by using a special printing device to give a lenticular picture. The present invention pertains to printing lenticular prints using a discontinuous method. Previous discontinuous methods of printing lenticular prints from input images can be further classified into two categories, namely segmented printing and composite printing. In segmented printing, the lenticular material is utilized as an image-forming element in the exposure process. If there are separate views to be printed to comprise the lenticular print, each view is recorded on a separate negative which is placed in the negative gate of an enlarger. These multiple views could have been simultaneously exposed by a multi-lens camera such as the 3D Magic camera made by Image Technology of Norcross, Georgia, which has three views, or by a single camera which is traversed in front of the scene between exposures. The enlarger is focused on a print gate with a lateral shift of the negative gate and enlarger lens establishing an angle of exposure correlated to the original angular parallax used in the camera optics. In composite printing, the information from the various views is combined into a composite print file which is printed directly onto the emulsion by an auxiliary optical system without reliance on the lenticular face plate to focus the information. An example of this is the Kodak Depth Imaging system which uses a Kodak LVT Film Recorder to print individual lines of information sampled from the different perspective views that could come from a camera such as the 3D Magic or from computer-generated or computer-altered images. This latter system produces a higher quality image, because the focus degradation associated with the lenticular face plate does not spread the information between adjacent views during the printing process, and color control can easily be incorporated in the printer exposure mechanism using lookup tables. As disclosed in EP-A-570807, after exposure and developing, the printed lines are carefully aligned with respect to the lenticular axis' orientation and the image is laminated to the back side of the lenticular face plate. This alignment procedure is facilitated by observing the Moire patterns generated between the printed image and the lenticular sheet while shifting or rotating the print. These patterns greatly magnify the errors of very small displacements. EP-A-560,180 describes a method and an apparatus for recording stereoscopic images on a recording medium having a lenticular array and a recording layer. The exposure of the light-sensitive medium is obtained after registration by a scan exposure from the rear side, and optionally a white layer made of titanium oxide or the like could be formed on the rear face of the recording medium. These is still a need to have a method and an apparatus which provides a high quality image by using a back exposure of the recording medium with an easy and robust registration step and means to obtain three-dimensional pictures which do not spread over adjacent views. SUMMARY OF THE INVENTION According to the invention such as disclosed in claim 1 or claim 3, it is proposed to expose the emulsion of the recording medium through the side opposite the lenticular side to avoid the degradation of focus discussed earlier. The means of exposing the emulsion could be either direct contact printing from a negative made on a line recorder such as the LVT Film Recorder or by optical projection with some magnification compensation from such a negative. It would also be possible to project an image from a CRT screen as with conventional CRT printing which would allow some electronic manipulation of image location and rotation. It is important that the lines of information be printed parallel to the lenticular axes and properly positioned with respect to their midpoints. It is therefore proposed to position a separate reference grid on the lenticular side of the coated material with a spatial pitch slightly different than the lenticular pitch so that a Moiré pattern of fringes becomes visible. This fringe pattern will greatly magnify any displacement or angular change in the position of the lenticular material from image to image and provide a feedback mechanism for repositioning the coated lenticular or the negative image prior to exposure. For setup purposes, a second reference grid can be temporarily placed in the negative gate or a reference grid printed on the negative at some place to the side of the final print format thereby allowing it to be trimmed away from the image after developing. In one embodiment of the present invention, there is provided a method and apparatus for producing a photographic print from an illuminated image comprising the steps of affixing a lenticular material over light sensitive material, positioning the light sensitive material on an exposure plane, and effecting the exposure of the light sensitive material from the side of the light sensitive material opposite the lenticular material, by light from the illuminated image. The invention further includes the optional step of affixing a reflective layer to the exposed side of said light sensitive material, after exposure and development, to reflect light back through the lenticular material. In another embodiment, a reference grid is arranged to be brought into contact with the lenticular side of said lenticular material so that a Moire fringe pattern is produced, the Moiré fringe pattern being compared to said fixed reference to determine the relative positions between said lenticular material and an illuminated image or negative. The present invention then, combines the effects of composite printing image quality by directly printing the recorded image lines of information with the reduced post exposure handling of precoated lenticular material. The present invention describes a means for making exposures of depth image information on precoated lenticular material without reliance on using the lenticular material in the exposure chain. Therefore, the fidelity of the images will be improved with less crosstalk between adjacent recorded lines of image information and special effects such as animation or image changes will be more distinct. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood when taken in conjunction with the description and drawings below wherein like characters indicate like parts and which drawings form a part of the present disclosure. Figure 1 shows a prior art segmented method of exposing the emulsion coating through the lenticular face plate; Figure 2 shows a prior art composite method of exposing the emulsion with a film recorder; Figure 3 shows the proposed method of exposing the emulsion from the back side by contact printing using a composite negative; Figure 4 shows the proposed method of exposing the emulsion from the back side by projection from a composite negative; Figure 5 shows a method of adjusting a projected image for rotation and lateral position to coincide with the orientation of the lenticular material for small errors; and Figure 6 shows a perspective view of the lenticular material and related Moire pattern. DETAILED DESCRIPTION OF THE DRAWINGS With more specific reference to Figure 1, there is shown a prior art technique of printing three-dimensional lenticular pictures on precoated lenticular material. A translatable film gate 100 is moved along a path including first, second and third positions, 111, 112 and 113, respectively. The film gate path is parallel to the plane of the precoated lenticular receiver material 104 and a projection lens 101 is moved along a mutually parallel path 108, including corresponding first, second and third locations 131, 132 and 133, respectively. At each location, an image of a negative placed in the film gate is focused onto the photosensitive layer 105 of the precoated lenticular receiver material 104 at a magnification which enlarges the negative area to match the print area. Lenticule 107 is shown for reference at the center of the print, but the principle herein described works for all lenticules in print. As the lens 101 is moved from position 131 successively to position 132 and eventually position 133, the film gate 100 follows in corresponding locations 111, 112, and 113 which maintains a coincidence of centerpoint of the film gate with optical projection paths 121, 122, and 123. To avoid gaps of unexposed receiver material between positions 131, 132 and 133, the exposing aperture of the lens 101 along path 108 should just touch the adjacent aperture. Since physical lens apertures are typically not that large, a common technique is to traverse the lens and negative with the existing aperture held open until midway points between positions 131 and 132, and 132 and 133 have been reached, at which time, the negative is changed. It is evident for the man skilled in the art that instead of a negative image, a positive image can be used with a positive light sensitive material. This motion can be achieved by a variety of means such as linkages, cam devices, stepper motors, or combinations thereof. Coincident with this motion, the actual negative present in the film gate is also changed, since the negatives represent differing perspective views taken at proportionally similar angles to the angles that paths 121, 122, and 123 respectively have relative to a perpendicular to the receiver material 104. These differing perspective view negatives can be provided by a movable camera on a rail or multi-lens camera such as the Nimslo camera. The quality of the image is directly affected if the alignments of: the negative within the film gate; the film to the lens; or, the lens to the lenticular; change due to machine inaccuracies or wear. If multiple images of a given subject are desired, this elaborate printing technique must be repeated, and subsequent images become degraded as the negative wears because of the negative transfer mechanism. The number of different perspective views printed is shown Figure 1 is three, but any number from one to n can be printed by this technique. Figure 2 shows a prior art method of exposing a photosensitive emulsion with a film recorder for later alignment and lamination. A film recorder such as the Kodak LVT Model 1620B is designed to affix a sheet of film 201 to the outside of cylindrical drum 202. The drum 202 is caused to rotated about its axis 203. A beam of exposing light is focused on the emulsion of a film sheet 201 using a microscope objective optic 204, and the exposing optical head 209 containing the optic 204 is transported along a path 205 which is parallel to axis 203 and the film surface. The amount of the exposing optics motion per revolution of drum 202 is made equal to the focused spot size on the film surface. This can be carefully maintained by changing the aperture size and shape of the beam. As the drum rotates to new unexposed film areas, the light entering the exposing optical head 209 is modulated for color content and intensity with values corresponding to image content. Since the time rate of image modulation, the time rate of rotation and the time rate of exposing optics translation are maintained at constant values, the resultant areas of exposure to modulation profiles are substantially the same, and commonly referred to as pixels, or picture elements. The progress of pixel information with respect to image content per revolution is rapid, since with only one revolution a whole line has been exposed, and this is called the fast scan direction. The progress of pixel information with respect to image content along the exposing optics translation path 205 is slower, since each revolution of the drum only permits a translation displacement equal to the focused spot size, and this is called the slow scan direction. The data providing the changing modulation control signals are provided by a control computer not shown, but a composite print file containing interleaved scan data from negatives provided can be suitably used to adjacent fast scan lines which correspond to the imaged lines from the optical paths 121, 122, 123 in Figure 1. The film sheet 201 can be developed, shown as process 210, to become film sheet 227 and aligned and laminated to a lenticular screen 228 of suitable lenticular spacing and thickness to accomplish the same final viewing projection task as faceplate 104 does. There can also be a laborious chain of events to produce a final depth image and the final quality subject to the accuracy of aligning and lamination. It has also been demonstrated in prior art that the film sheet 201 can be comprised of negative material and that an additional contact printing operation can be inserted after developing 210 to provide contact print copies 227 for final assembly. The quality of image produced by this process is better than that illustrated in Figure 1, because of the effects of the lenticular sheet as an optical imager are excluded. Figure 3 shows the proposed method of exposing the emulsion from the back side by contact-copying a composite negative and subsequest alignment of the receiver material for exposing. A referenced grid 301 composed of black lines and clear spaces is provided which has the same spatial pitch as the lenticules on the precoated lenticular receiver material 304. A negative produced on a film recorder as described for Figure 2 will have multiple lines per lenticule. The relative location and rotation of the negative 302 to the reference grid 301 can be benchmarked by observing the Moiré patterns set up between the lines of the reference grid 301 and the lines on the negative 302 when the two components are translated to contact each other along paths 307 and 303 respectively. Paths 307 and 303 are made parallel by machine design and fixturing. Prior to exposing the lenticular receiver material 304, comprised of lenticular sheet 306 and photosensitive layer 305, the receiver material 304 can be aligned for position and angle to the grid 301 by bringing grid 301 in contact with sheet 306 along path 307 and adjusting until the same Moire pattern as previously benchmarked has been achieved. Then the negative 302 can be translated along path 303 to contact the photosensitive layer 305 and an exposure made by illuminating negative 302 from the bottom side, with the assurance that the exposed lines on the negative 302 will be aligned to the lenticules of sheet 306. Figure 6 shows the rotational motion "e" is best measured by placing pieces of the reference grid 301 at opposite ends of the lenticular print. These areas could be located just outside the actual print area in a border. That would allow monitoring and adjusting the alignment and rotation for each print on a continuous web of precoated lenticular receiver material 306 extending in the direction of the lenticules. Figure 4 shows the proposed method of exposing the emulsion from the back side by optical projection from a composite negative. The reference grid 401 which can be moved to a contact position with precoated lenticular receiver material 404 along path 407 can similarly be used as in the contact process described in Figure 3 to pre-align a negative 402 similarly consisting of multiple lines per lenticule. As an additional aid to observing the Moiré pattern, a grid pattern 409 can be printed on the negative outside the image area. A printer lens 403 is used to project the negative image onto the photosensitive emulsion layer 405. Prior to inserting the material 404 into the printing gate established by datums or markers 410 and 411, the reference grid 401 is moved to datum 410 and the Moiré pattern between it and the image of the grid pattern 409 benchmarked as described earlier. The material 404 can now be inserted in the printing gate between the markers 410 and 411, and a similar Moire pattern achieved by adjusting the position of the material 404 for position and rotation. The light source 408 can now be turned on and the image of the negative will be printed on the layer 405. Figure 5 shows a preferred embodiment of the projection method described in Figure 4 for a printer designed to print multiple images on a web of precoated lenticular receiver material 504. This entire apparatus is inverted from the orientation shown in Figure 4 for the sake of drawing clarity, but the final orientation would be chosen for machine design efficiency. Lens 503 provides an image 506 of the negative 502 on layer 505. Reference grids 500 and 501 are positioned to extend beneath the receiver material 504. The grids 500 and 501 can be provided to pre-align the rotation 'e' of negative 502 as described for Figure 4. The Moiré pattern is benchmarked by observing the patterns with video cameras, the lenses 510 and 511 of which, are shown below the web 504. Since lateral movement of web 504 may be difficult, the image 506 of the negative 502 can be laterally shifted by using a dithering prism 512 comprised of a small wedge angle between two flat surfaces on a disk of glass. As the prism 512 is rotated, the image will deviate slightly in a direction perpendicular to the wedge surface intersection line. Therefore, the amount of lateral shift of the image can be changed by rotating prism 512. The method and apparatus of the present invention has been described in connection with the preferred embodiment as disclosed herein. Although an embodiment of the present invention has been shown and described in detail herein, along with certain variants thereof, many other varied embodiments that incorporate the teachings of the invention may be easily constructed by those skilled in the art. Accordingly, the present invention is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the scope of the invention as defined by the claims.

Claims: A method of producing from an original image (302; 402; 502) a photographic print on a recording medium (304; 404; 504), said medium having a first planar side placed next to a light sensitive material (305; 405; 505) and a lenticular side, said method comprising the steps of: (a) positioning the recording medium on an exposure plane; (b) aligning said recording medium with respect to the original image; and (c) effecting the exposure of the light sensitive material from the side of the light sensitive material opposite the lenticular array, by light from the original; and characterized in that (d) said step of aligning comprises (d1) projecting a reference grid (301; 401; 500, 501) onto the lenticular side of the recording medium to generate a Moiré fringe pattern; (d2) detecting the generated Moiré fringe pattern; (d3) adjusting (e) the position of the recording medium with respect to the referenced grid in dependence of the detected Moiré pattern. The method as set forth in claim 1, wherein said step of projecting a reference grid includes the step of providing at least two reference grids (500, 501) at positions displaced along the direction of the axes of the lenticules of the lenticular material. A printing apparatus for producing an image print from an illuminated original image (302; 402; 502) on a recording medium (304; 404; 504) including a lenticular side (306; 506) and a smooth side provided with a light sensitive layer (305; 405; 505), said apparatus comprising: a mounting device for placing said recording medium thereon; a device (408; 503) for providing an imagewise pattern of said original image to be printed on said light sensitive layer; and characterized by : said mounting device being operable to selectively adjust the position of said recording medium; means for illuminating and projecting a reference grid (301; 401; 500, 501) onto a surface of said lenticular recording medium in order to generate a Moiré fringe pattern; means for sensing (510, 511) the generated Moiré fringe pattern; and means (e, 512) for adjusting the position of said mounting device in response to the detected pattern of Moiré fringes. The printing apparatus as set forth in claim 3, wherein said lenticular recording medium is comprised of a plurality of juxtaposed lenticules having a first pitch and said reference grid includes a series of parallel lines having a second pitch between said lines, said second pitch being different from said first pitch such that a Moiré fringe pattern is produced.

Inventors: FOGEL SERGEI V, TAYLOR ROY Y, FOGEL, SERGEI V., TAYLOR, ROY Y.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1996
Main classification: G03B35
IPC codes: G03B35, G03C9, G03B27, G03C7, G02B27