Abstract:
An illumination obscurement device for controlling the obscurement of illumination from a light source which is optimized for use with a rectangular, arrayed, selective reflection device. In a preferred embodiment, a rotatable shutter with three positions is placed between a light source and a DMD. The first position of the shutter is a mask, preferably an out of focus circle. This out of focus circle creates a circular mask and changes any unwanted dim reflection to a circular shape. The second position of the shutter is completely open, allowing substantially all the light to pass. The third position of the shutter is completely closed, blocking substantially all the light from passing. By controlling the penumbra illumination surrounding the desired illumination, DMDs can be used in illumination devices without creating undesirable rectangular penumbras.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/724,588, filed Nov. 28, 2000 now U.S. Pat. No. 6,536,922, which is a divisional of U.S. application Ser. No. 09/711,355, filed Nov. 9, 2000 now U.S. Pat. No. 6,601,974, which is a divisional of U.S. application Ser. No. 09/108,263, filed Jul. 1, 1998 now U.S. Pat. No. 6,220,730. 
    
    
     TECHNICAL FIELD 
     The present disclosure describes a special image obscurement device for a light source. 
     BACKGROUND 
     In live dramatic performances controlled lighting is often used to illuminate a performer or other item of interest. The illuminated area for live dramatic performance is conventionally a circular beam of light called a “spot light.” This spot light has been formed from a bulb reflected by a spherical, parabolic, or ellipsoidal reflector. The combination forms a round beam due to the circular nature of reflectors and lenses. 
     The beam is often shaped by gobos.  FIG. 1  shows a light source  100  with reflector  101  projecting light through a triangular gobo  108  to the target  105 . The metal gobo  108  as shown is a sheet of material with an aperture  110  in the shape of the desired illumination. Here, that aperture  110  is triangular, but more generally it could be any shape. The gobo  108  restricts the amount of light which passes from the light source  100  to the imaging lenses  103 . As a result, the pattern of light  106  imaged on the stage  105  conforms to the shape of the aperture  110  in the gobo  108 . 
     Light and Sound Design, the assignee of this application, have pioneered an alternate approach of forming the gobo from multiple selected reflective silicon micromirrors. One such array is called a digital mirror device (“DMD”) where individual mirrors are controlled by digital signals. See U.S. Pat. No. 5,828,485 the disclosures of which are herein incorporated by reference. DMDs have typically been used for projecting images from video sources. Because video images are typically rectangular, the mirrors of DMDs are arranged in a rectangular array of rows and columns. 
     The individual mirrors  370  of a DMD are rotatable. Each mirror is mounted on a hinge  372  such that it can rotate in place around the axis formed by the hinge  372 . Using this rotation, individual mirrors  370  can be turned “on” and “off” to restrict the available reflective surface. 
       FIG. 2  shows an example of using a DMD  400  to project a triangular illumination by turning “off” some of the mirrors in the DMD  400 . The surface of the DMD  400  exposed to a light source  402  comprises three portions. The individual mirrors which are turned “on” (toward the light source  402 ) make up an active portion  404 . In  FIG. 3A , the active portion  404  is triangular. The individual mirrors which are turned “off” (away from the light source  402 ) make up an inactive portion  406 . These pixels are reflected. The third portion is a surrounding edge  408  of the DMD  400 . Each of these portions of the DMD  400  reflects light from the light source  402  to different degrees. 
       FIG. 3A  shows a resulting illumination pattern  410  with the active area  404  inactive area  406  and cage  408 . 
     SUMMARY 
     The inventors recognize that light reflected from the inactive portion  406  of the DMD  400  generates a dim rectangular penumbra  418  area is surrounding the bright desired area  404 . Light reflected from the edge  408  of the DMD  400  generates a dim frame area. The inventors recognized that this rectangular penumbra  418  is not desirable. 
     The inventors also recognized that a circular penumbra is much less noticeable in the context of illumination used in dramatic lighting. 
     Accordingly the inventors have determined that it would be desirable to have a device which would provide a circular illumination without a rectangular penumbra while using a rectangular arrayed device as an imaging surface. The present disclosure provides such capabilities. 
     This disclosure describes controlling illumination from a light source. The disclosed system is optimized for use with a rectangular, arrayed, selective imaging device. 
     In a preferred embodiment, a rotatable shutter with three positions is placed between a DMD and the imaging optical system. The first position of the shutter is a mask, preferably a circle, placed at a point in the optical system to be slightly out of focus. This circle creates a circular mask and changes any unwanted dim reflection to a circular shape. The second position of the shutter is completely open, allowing substantially all the light to pass. The third position of the shutter is completely closed, blocking substantially all the light from passing. 
     An alternate embodiment for blocking the rectangular penumbra by changing any penumbra to round uses an iris shutter placed between a DMD and increases optics. The iris shutter creates a variable aperture which ranges from completely closed to completely open. Intermediate settings include circles of varying diameter, resulting in similar projections as with the first position of the shutter embodiment. 
     Another alternate embodiment for blocking the rectangular penumbra by changing any penumbra to round uses two reflective surfaces. The first reflective surface is a DMD. The second reflective surface is preferably a light-sensitive reflective surface such as a polymer. If the light striking a portion of the reflective surface is not sufficiently bright, that portion will not reflect the full amount of that light. 
     By controlling the penumbra illumination surrounding the desired illumination, DMDs and other pixel-based rectangular elements can be used in illumination devices without creating undesirable rectangular penumbras. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a conventional illumination device including a gobo. 
         FIG. 2  shows an illumination device including a DMD. 
         FIGS. 3A–3G  shows a illumination patterns. 
         FIG. 4  show the optical train. 
         FIG. 5  shows a three position shutter according to a preferred embodiment of the present invention. 
         FIG. 6A  shows an illumination device including a three position shutter according to a preferred embodiment of the present invention which is set to a mask position. 
         FIG. 6B  shows an illumination pattern resulting from the device shown in  FIG. 6A . 
         FIG. 7  shows an iris-type shutter. 
         FIGS. 8A and 8B  show use of the adjustable iris in a DMD system. 
         FIG. 9  shows a three-position shutter with an iris system. 
         FIG. 10  shows an embodiment with a light. 
     
    
    
     DETAILED DESCRIPTION 
     The structure and operational parameters of preferred embodiments will be explained below making reference to the drawings. 
     The present system uses two different operations to minimize the viewable effect of the unintentional illumination, or penumbra, discussed previously. A first operation forms the optics of the system in a way which prevents certain light from being focused on the DMD and hence prevents that light from being reflected. By appropriately masking the incoming light to the DMD, certain edge portions the penumbra can be masked. A second part of the system uses a special illumination shutter to provide different shaped penumbras when desired. 
     The overall optical system is shown in  FIG. 4 . The bulb assembly  200  includes a high wattage bulb, here an MSR 1200 SA Xenon bulb  202  and retroreflectors  204  which capture some of the output from that bulb. The output of the bulb is coupled to a dichroic or “cold” mirror  206  which reflects the visible light while passing certain portions of the infrared. The first focus of the reflector is at Point  208 . A DMD mask is located at that point. The DMD mask is preferably rectangular, and substantially precisely the shape of the inner area  418  of the DMD. The image of the mask is also focused onto the DMD: such that if one were looking at the mask from the position of the DMD, one would see the mask clearly and in focus. 
     A first color system includes an RGB system  210  and a parametric color system  212 . The light passes through all of these elements and is then further processed by an illumination relay lens  214  and then by an imaging relay lens  216 . The image relay lens  216  has an aperture of 35 millimeters by 48 millimeters. The output is focused through a field lens  218  to the DMD  400 . The off pixels are coupled to heat sink  220 , and the on pixels are coupled via path  222  back through the imaging relay  216  folded in the further optics  224  and finally coupled to zoom elements  230 . The zoom elements control the amount of zoom of the light beam. The light is colored by a designer color wheel  232  and finally focused by a final focus element  235  controlled by motor assembly  236 . 
     The way in which the outer penumbra is removed will be explained with reference to  FIGS. 3A and 8B . 
       FIG. 3B  shows the front surface of the DMD. This includes a relatively small inner active portion  350  which includes the movable mirrors. Active portion  350  is surrounded by a white inactive portion  352  which is surrounded by packaging portion  354 , a gold package  356 , and a ceramic package  358 . Light is input at a 20° angle from the perpendicular. The reason why becomes apparent when one considers  FIG. 3C . The mirrors in the DMD tip by 10°. 
       FIG. 3C  shows two exemplary mirrors, one mirror  360  being on, and the other mirror  362  being off. Input light  362  is input at a 20° angle. Hence, light from the on mirror emerges from the DMD perpendicular to its front surface shown as  364 . However, the same light  362  impinging on an off mirror emerges at a different angle shown as  366 . The difference between those two angles forms the difference  367  between undesired light and desired light. However, note in  FIG. 3C  what happens when the incoming light  362  hits a flat surface. Note the outgoing beam  368  is at a different angle than either the off position or the on position. The hypothetical beam  366  from an off mirror is also shown. 
     The inventors recognize, therefore, that a lot of this information falls within an undesired cone of light. All light which is input (e.g. 362 rays can be filtered by removing the undesired cone. This is done according to the present disclosure by stopping down the cone of light to about 18° on each side. The final result is shown in  FIG. 3D . The incoming light is stopped down to a cone of 18° by an F/3.2 lens. The incoming light is coupled to the surface of the DMD  400 , and the outgoing light is also stopped to a cone of 18°. These cones in the optical systems are identified such that the exit cone does not overlap with the undesired cone  367  shown in  FIG. 3C . 
     This operation is made possible by appropriate two-dimensional selection of the incoming light to the digital mirror.  FIG. 3E  shows the active portion  350  of the digital mirror. Each pixel is a rectangular mirror  370 , hinged on axis  372 . In order to allow use of this mirror and its hinge, the light needs to be input at a 45° angle to the mirror, shown as incident light ray  374 . The inventors recognized, however, that light can be anywhere on the plane defined by the line  374  and perpendicular to the plane of the paper in  FIG. 3E . Hence, the light of this embodiment is input at the  FIG. 3F  which represents a cross section along the line  3 F– 3 F. This complex angle enables using a plane of light which has no interference from the undesired portions of the light. Hence, by using the specific desired lenses, reflections of random scattered illumination is bouncing off the other parts is removed. This masking carried out by at least one of the DMD mask  208  and the DMD lens  218 . By appropriate selection of the input light, the output light has a profile as shown in  FIG. 3G. 350  represents the DMD active area,  356  represents the package edge, and  358  represents the mount. The light output is only from the DMD active area and is stopped and focused by appropriate lenses as shown in  FIG. 3G . 
       FIG. 5  shows a planar view of a shutter  500  according to a preferred embodiment of the invention. The preferred configuration of the shutter  500  is a disk divided into three sections. Each section represents one position to which the shutter  500  may be set. The shutter  500  is preferably rotated about the center point  502  of the shutter. The gate of the light is off center, to allow it to interact with one of the three sections. Rotation is preferred because rotation allows efficient transition between positions. Alternately, the shutter  500  may slide vertically or horizontally to change from one position to another. A round shape is preferred because of efficiency in material and space use. Alternately, the shutter  500  may be rectangular or some other polygonal shape. 
     Three positions are preferred because each position is rotatably equidistant from the other positions. However, a shutter  500  with three positions provides more positions than a shutter  500  with only two positions. 
     In a preferred embodiment, a first position is a mask position  504 . The mask position  504  includes an open or transparent aperture  506  and an opaque mask portion  503  which is not permeable to light. Preferably, material is removed from the shutter  500  leaving a shaped aperture  506  and a mask portion  508 . 
     The second position is an open position  510 . The open position  510  includes an opening  512 . Preferably the opening  512  is formed by removing substantially all material from the shutter  500  in the section of the open position  510 . 
     The third position is a closed position  514 . The closed position  514  includes a opaque barrier portion  516 . Preferably, the barrier portion  516  is just a solid block of material. 
       FIG. 6A  shows a preferred embodiment of an illumination system. A shutter  500  of the type shown in  FIG. 5  is rotatably mounted between a light source  602 /DMD  604  such that substantially all the light from the light source  602  strikes only one section of the shutter  500  at a time. The shutter  500  is rotatably positioned to the mask position  504 . Thus, when the light source  602  is activated, light from the light source  602  reflected by DMD  604  strikes only the mask position  504  of the shutter  500 . 
     Using digital control signals, the DMD  604  is set so is that an active portion  612  of the individual mirrors are turned “on” and an inactive portion of the individual mirrors are turned “off” (see  FIG. 4A ). The shape of the active portion  612  is set to conform to the desired shape of the bright portion of the illumination reflected by the DMD  604  shown in  FIG. 6B , described below. 
       FIG. 6B  shows an illumination pattern generated by the illumination device  600  configured as shown in  FIG. 6A . 
     Returning to  FIGS. 3A and 3B , when the shutter  500  is not interposed between the DMD  400  and the stage. All portions of the DMD  400  reflect the light and create the undesirable illumination pattern shown in  FIG. 3A . In particular, the bright circular area  404  is surrounded by an undesirable dim rectangular penumbra  418  and slightly brighter frame  422 . 
     As described above, the illumination pattern shown in  FIG. 6B  does not include a dim rectangular penumbra  418  and a slightly brighter frame  422 . These undesirable projections are substantially eliminated by using the shutter  500  and the aperture  506 . A dim penumbra illumination is generated by light reflecting from the inactive portion  604  of the DMD  604 . This dim circular penumbra illumination is more desirable than the dim rectangular penumbra and slightly brighter frame  422  of  FIG. 3A  because the shape of the dim penumbra illumination is controlled by the shape of the aperture  506 . Accordingly, the dim penumbra illumination can be conformed to a desirable shape. 
       FIG. 7  shows an alternate embodiment for an iris shutter  900 . Preferably, a series of opaque plates  902  are arranged inside a ring  904  to form an iris diaphragm. By turning the ring  904  the plates  902  move so that an iris aperture  906  in the center of the iris shutter  900  varies in diameter. The iris aperture  906  preferably varies from closed to a desired maximum open diameter. Preferably the iris shutter  900  can transition from closed to a maximum diameter (or the reverse) in 0.1 seconds or less. 
       FIG. 8A  shows an illumination device  1000  including an iris shutter  900  as shown in  FIG. 7 . The iris shutter  900  is positioned between a DMD  1004  and a stage  1002 . In  FIG. 8A , the iris shutter  900  is partially open such that the iris aperture  906  allows part of the light  1006 ,  1008  from the light source  1002  to pass through, similar to the mask position  504  of the three position shutter  500  shown in  FIG. 5 . One difference between the mask position  504  and the iris shutter  900  is that the iris aperture  906  is variable in diameter while the aperture  506  of the mask position  504  is fixed. The remainder of the light  1010  from the light source  1002  is blocked by the plates  902  of the iris shutter  900 . The light  1006 ,  1008  which passes through the iris aperture  906  strikes the DMD  1004  in a pattern  1012  which is the same shape as the shape of the iris aperture  906 . Through digital control signals, some of the individual mirrors of the DMD  1004  are turned “on” to form an active portion  1014 , and some of the individual mirrors are turned “off” to form an inactive region  1016 . Preferably, the pattern  1012  is at least as large as the active portion  1014  of the DMD. 
       FIG. 10B  shows an illumination pattern  1018  generated by the illumination device  1000  shown in  FIG. 10A . Similar to  FIGS. 6A and 6B , a bright illumination  1020  is generated by light  1022 ,  1020  reflected from the active portion  1014  of the DMD  1004 . A dim penumbra illumination  1024  is generated by light  1026  reflected from the inactive portion  1016  of the DMD  1004 . By varying the diameter of the iris aperture  906 , the size of the pattern  1012  on the DMD  1004  changes. As the pattern  1012  changes the amount of the inactive portion  1016  of the DMD  1004  which is struck by light  1008  from the light source  1002  changes and so the dim penumbra  1024  changes as well. 
       FIG. 9  shows an alternate embodiment of a shutter  1100  which combines features of a three position shutter  500  with an iris shutter  900 . The overall configuration of this shutter  1100  is that of the three position shutter  500 . However, instead of the mask portion  504  as shown in  FIG. 5  and  FIG. 6A , one of the positions is an iris portion  1102 . The iris portion  1102  has an iris diaphragm  1104  inserted into the material of the shutter  1100 . Similar to the iris shutter  900  of  FIG. 7 , the iris diaphragm  1104  is made from a series of opaque plates  1106  arranged inside a ring  1108 . By turning the ring  1108  the plates  1106  move so that an iris aperture  1110  in the center of the iris diaphragm  1104  varies in diameter. This configuration operates in most respects similarly to the three position shutter  500  as shown in  FIG. 5  and  FIG. 6A . Because of the iris diaphragm  1104 , the amount of light blocked by the iris portion  1102  is variable. 
       FIG. 10  shows an alternate embodiment of an illumination device  1200  which includes a second reflective surface  1202 . A light source  1204  projects light onto a DMD  1206  which has an active portion  1208  and an inactive portion  1210 . Light reflects off the DMD  1206  and strikes the second reflective surface  1220 . The second reflective surface  1220  acts to reduce the dim penumbra and frame created by the inactive portion  1210  and edge  1212  of the DMD  1206  (recall  FIGS. 3A and 3B ), leaving the active portion  1222 , to project image  1246 . 
     In the embodiment shown in  FIG. 10 , the second reflective surface  1220  is a light sensitive surface such as an array of light trigger cells. Only light of a certain brightness is reflected. If the light striking a cell is insufficiently bright, substantially no light is reflected by that cell. Alternately, the second reflective surface  1220  may be made of a polymer material that only reflects or passes light of sufficient brightness. Light  1214  reflected from the active portion  1208  of the DMD  1206  is preferably bright enough to be reflected from the second reflective surface  1202 . Light  1216 ,  1218  reflected from the inactive portion  1210  and the edge  1214  of the DMD  1206  is preferably not bright enough to be reflected from the second reflective surface  1202 . Thus, only light  1214  from the active portion  1208  of the DMD  1206  will be reflected from the second reflective surface  1202 . As described above, the undesirable dim rectangular penumbra  418  and slightly brighter frame  422  (recall  FIG. 4B ) would be created by light  1216 ,  1218  reflected from the inactive portion  1210  and edge  1212  of the DMD  1206 . The second reflective surface  1202  does not reflect this dim light  1216 ,  1218  and so wholly eliminates the dim penumbra and frame from the resulting illumination. 
     A number of embodiments of the present invention have been described which provide controlled obscurement of illumination. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, filters or lenses might be introduced to the illumination device  600  shown in  FIG. 6A  between the shutter  500  and the DMD  604 . Alternately, the light source might be a video projection device or a laser. 
     While this disclosure describes blocking the light before impinging on the DMD, it should be understood that this same device could be used anywhere in the optical train, including downstream of the DMD. Preferably the blocking is at an out of focus location to soften the edge of the penumbra, but could be in-focus. 
     The light reflecting device could be any such device, including a DMD, a grating light valve (“GLV”), or any other arrayed reflecting device which has a non-circular shape. 
     All such modifications are intended to be encompassed in the following claims.