Support apparatus and method for use with a camera and strobe lights

A support apparatus for a camera and strobe lights includes a mounting plate for holding the camera substantially normal to and at a fixed distance from the photograph area, a set of legs attached to one or more portions of the apparatus providing support and positions for mounting and a set of strobe lights affixed to the legs at known positions relative to the focal plane of the camera and directed towards the photograph area to facilitate acquisition of multiple photographic images for use in one or image processing operations. The support apparatus can be automated through the use of one or more mobile strobe lights slidably coupled to each leg, capable of self-propelled linear motion along the axis of the leg and providing indication of its position along the leg to facilitate acquisition of multiple photographic images and position data for the image processing operations.

BACKGROUND

The present invention relates to a camera support device for taking photos. Many digital image processing operations require specialized equipment to gather data before the digital image processing technique can be performed. Polynomial texture mapping is one such digital image processing technique. The technique is described in U.S. Pat. No. 6,515,674 issued Feb. 4, 2003 assigned to the assignee of the present invention and entitled “Apparatus for and of Rendering 3D Objects with Parametric Texture Maps,” by Gelb, Wolters, and Malzbender, as well as in “Polynomial Texture Maps,” by T. Malzbender, D. Gelb, and H. Wolters, InProceedings of ACM SIGGRAPH2001, pp. 519–528, Aug. 12–17, 2001.

Once photos are taken with the equipment, polynomial texture mapping processing allows the user to interactively alter the apparent position of the light source in an image as well as its apparent image texture while observing the image on a computer display. For example, a photograph of a valuable archeological artifact can be processed in such a way as the light source can appear directly over the artifact, yielding a low-contrast image. Similarly, the apparent position of the light source can be moved to a very low angle with respect to the artifact, producing a higher contrast image. Beyond this, the apparent surface texture and color of the artifact can be changed from dry and dull white to an oily shiny black finish with the tiny details highlighted by specular reflections.

Powerful visual results from polynomial texture mapping make it a useful technique for the close examination of precious artifacts or forensic evidentiary material that is subject to rigorous handling restrictions. Unfortunately, this technique is currently restricted to the laboratory, because a large hemispherical dome used to support the camera and various strobe lights is bulky and difficult to transport. Consequently, this makes in situ examination of artifacts or evidentiary material problematic and limits the use of this image processing technique.

Other powerful image processing techniques also require specialized equipment to obtain photographs. These other image processing techniques requiring extensive equipment and lighting may also be limited to a laboratory setting like polynomial texture mapping. Accordingly, there is a need to develop more portable and cost-effective equipment for gathering data for use with polynomial texture mapping and other image processing operations.

SUMMARY OF THE INVENTION

One aspect of the present invention features a support apparatus for a camera and strobe lights. The support apparatus includes a mounting plate for holding the camera above and at a fixed distance from the photograph area, a set of legs attached to one or more portions of the apparatus providing support and positions for mounting and a set of strobe lights affixed to the legs at known positions relative to the focal plane of the camera and directed towards the photograph area to facilitate acquisition of multiple photographic images capable of use in one or more image processing operations.

Another aspect of the present invention also features a support apparatus for a camera and strobe lights. This support apparatus includes a mounting plate for holding the camera above and at a fixed distance from the photograph area, a set of legs attached to one or more portions of the apparatus providing support and positions for mounting and a mobile strobe light slidably coupled to each leg, capable of self-propelled linear motion along the axis of the leg and providing indication of its position along the leg to facilitate acquisition of multiple photographic images capable of use in one or more image processing operations.

DETAILED DESCRIPTION

Embodiments of the present invention concern the use of specialized data gathering equipment for various image-processing operations. While the description contained herein describes polynomial texture mapping as one image processing operation, many other image processing operations would also benefit from embodiments of the present invention. For example, alternate embodiments could be used to gather data for an image processing technique called “shape from shading” that recreates the shape of an object according to the various shades and/or shadows caused by the interplay of light upon the object. Accordingly, the mention of polynomial texture mapping is described as a convenient way of describing one embodiment of the present invention and should not serve to limit any aspect of the invention to polynomial texture mapping or any particular feature included or excluded specifically for this one purpose or application.

Polynomial texture mapping is one exemplary image processing operation that allows an image of an object to be interactively manipulated in a way as to reveal extremely fine or faint details. The details revealed are far beyond those revealed by simple contrast enhancement of an ordinary photograph. This ability to enhance and reveal extremely faint detail makes polynomial texture mapping a valuable tool for in situ forensic evidentiary examination, archeological artifact examination, and other detailed study where there is insufficient detail exhibited by ordinary photographs.

The data for polynomial texture mapping includes multiple images of a specimen object. The images are taken with a digital camera in a fixed position above the object. Each image is lit by a light source at a different position. Typically, a number of different angles around the object (azimuth) and different elevations with respect to the horizontal plane of the object are used to position the light source for each image. These angles around the object are also referred to as azimuth positions.

Aspects of the present invention are advantageous in at least one or more of the following ways.

Embodiments of the present invention allow the image data for polynomial texture mapping to be easily collected in the field using a portable support apparatus for the camera and strobe lights. The support apparatus comprises a special camera mounting plate that allows the camera to take photographs through an aperture in the mounting plate. This allows the camera to be positioned at a fixed distance above the area being photographed. The legs, which can be attached to the mounting plate, further providing support for the strobe lights.

Strobe lights mounted on different legs allow different azimuthal images to be acquired as rapidly as the camera can be cycled and the strobe lights flashed. The strobe lights are slidable along the length of the legs and fixable at known distances from the focal plane of the camera. Strobe lights mounted at or moved to different points of fixation along the length of the leg allow different elevation images to be acquired. Additionally, the strobe lights are rotatable around the axis of the leg facilitating compaction and transportation of the support apparatus.

Further embodiments of the present invention allow the strobe lights to move automatically along the length of the leg. This allows the rapid and accurate collection of large numbers of images for polynomial texture mapping. This is highly advantageous to the gathering of forensic evidence where time at the scene of the evidence may be limited and accuracy in obtaining evidentiary material is of the utmost importance.

While not illustrated specifically, additional legs can be added to increase the number of azimuthal positions for the lights. These additional legs can provide added support for the overall structure or apparatus or may extend downward without contacting the ground or providing further support. For example, a tripod is illustrated using these support legs. However, a lesser or greater number of legs can be used to support the apparatus. Moreover, a monopod (i.e., one support leg) can be combined with several non-supporting legs extending downward to provide additional azimuthal mounting points for lighting and other accessories. This monopod would be highly portable and functional, yet may be less stable in operation

Turning first toFIG. 1A, a perspective view of the camera and strobe support apparatus is illustrated according to one embodiment of the present invention. A camera102is mounted facing down towards a photograph area110and is supported by a mounting plate104. Mounting plate104has an aperture105that allows the camera102to see a photograph area110. A set of legs106, connected to mounting plate104, supports mounting plate104and camera102in a stable manner. Connected to legs106is a set of strobe lights108that can be directed towards a specimen object112within photograph area110. The portability of the support apparatus allows camera102to be positioned above the specimen object112.FIG. 1Bshows light-shielding screens114attached between legs106.

Camera102is generally a digital camera. The digital camera is advantageous to polynomial texture mapping because polynomial texture mapping readily adapts to the camera's digital image data. It is also very convenient to use digital photography. For example, having the image in digital form eliminates the time-consuming steps of film development and digital scanning of multiple film images.

Mounting plate104holds the camera102with its lens facing down and substantially normal to and at a fixed distance from the area being photographed. Aperture105in mounting plate104allows the camera to see photograph area110directly beneath camera102. In alternate embodiments, camera102is mounted on the bottom surface of mounting plate104or mounting plate104is comprised of an optically clear material with camera102mounted on its upper surface. Legs106securely support the mounting plate.

In one embodiment of the present invention, legs106are a set of three legs attached to mounting plate104that form a tripod. In yet another embodiment, legs106have a telescoping feature to aid in the compaction and transportation of the support apparatus.

Attached to legs106are strobe lights108. The various mounting points of strobe lights108allow acquisition of a number of differently lit images of specimen object112. For each image, a single strobe light from strobe lights108is flashed or “fired” while the shutter of camera102is open. Additionally, each image is lit by a differently positioned strobe light in strobe lights108. In other words, for polynomial texture mapping, no two images in the image set are lit from the same position.

The firing of the strobe lights108can be accomplished with a sequencing device. Using the sequencing device, the shutter of camera102is opened, a single strobe light from strobe lights108is fired once, and then the shutter of camera102is closed. The captured image is stored and a different strobe light from strobe lights108is selected and the process is repeated until all strobe lights108have been fired. Moving the strobes to different known positions along legs106and repeating the above sequence allows the acquisition of additional images.

Frequently, in forensic evidentiary photography, archeological photography, or in other photographic scenes, it is desirable to photograph specimen object112in situ without disturbing either the object or its environment. The portability of the support apparatus allows it to be positioned so that specimen object112resides within the center of photograph area110. In police work, in situ photography and evidence gathering is particularly important. For example, frequent moving or handling of evidentiary material may result in a complex chain of custody. This chain of custody may impact the value of the evidence due to the increased possibility of tampering or contamination. Using polynomial texture mapping photography to capture evidence in situ results in a shorter chain of custody and increased evidentiary value of specimen112and other photographed items.

As previously described, polynomial texture mapping relies on a set of data images, each lit from a different single point. It is therefore desirable to exclude ambient light from the area being photographed110. Light-shielding screens114, shown inFIG. 1B, serve to block out ambient light and ensure that each image is lit by light from only the strobe light that is fired. In one embodiment of the present invention, light-shielding screens114are attached between adjacent legs106. The screens can be composed of either rigid or flexible material. In another embodiment of the present invention, screens114roll out from legs106and attach to adjacent legs106. Alternate embodiments that construct the screens114from a material that blocks infrared as well as ultraviolet light allow polynomial texture mapping to be performed with light frequencies outside the visible spectrum.

Turning now toFIG. 2, a side view of the support apparatus according to one embodiment of the present invention. A camera202is attached to a camera bracket210, which in turn is attached to a mounting plate212. Attached to camera202is its lens204, which forms a focused image at the focal plane206of the camera202. Mounting plate212has an aperture213allowing the camera's field of view208to be unobstructed by mounting plate212. Attached to the mounting plate212is a set of legs214. Attached to legs214is a set of strobe light assemblies as exemplified by strobe light assembly215. In one embodiment, strobe light assembly215is comprised of a swivel mounting-ring216connected to its associated leg214. A ball joint218connects swivel mounting-ring216to a strobe light body220. Attached to strobe light body220is a strobe lamp reflector and lens222.

As previously described, camera202is typically a digital camera that mounts, with lens204facing down along the length of camera mounting-bracket210. With conventional camera tripods, this type of mounting is problematic due to the obstruction of the camera's field of view by either the mounting plate or the legs. Embodiments of the present invention employ a mounting plate with an aperture213allowing the camera's field of view208to be unobstructed by either mounting plate212or legs214.

Camera lens204can be either a fixed focal length lens or it can be a variable focal length zoom lens. The zoom lens allows optimal framing of the object being photographed, yielding more detail. In either of these lens embodiments, the shorter the lens focal length, the wider the field of view208.

Camera lens204typically has a built-in automatic diaphragm to control the depth of focus and the amount of light reaching the image sensor (not shown) mounted inside the camera at the focal plane206. This type of lens is termed an “automatic lens.” An automatic lens allows focusing with its diaphragm set at its widest opening. This yields a bright image with a narrow depth of field, allowing the proper focus to be readily determined.

In one embodiment of the present invention, three of legs214form a tripod. The tripod configuration of the legs provides a stable structure for the support apparatus. Legs214are provided with detents at known positions so that various strobe light assemblies such as strobe light assembly215can be placed at different positions along the leg to increase the number of images for the polynomial texture mapping data set. The detent positions can be linearly spaced or non-linearly spaced along the length of the leg. For example, one non-linear spacing of the detents can make moving to the next detent result in a constant elevation angle displacement with respect to the horizontal plane. Fixed detent positions are advantageous because they reduce the error in the placement of strobe assembly215.

In another embodiment, the strobe assembly215can be affixable along the axis of a bar mounted at least at one point to at least one leg. For example, mounting the strobe assembly215at different points along a bar mounted horizontally between two legs would result in a different azimuth angle for the strobe light as it was affixed at each mounting point.

Swivel mounting-ring216attaches strobe assembly215to each of legs214in a slidable manner. In addition to permitting strobe assembly215to be moved up and down the leg, swivel ring216allows strobe assembly215to be rotated around the axis of the leg, allowing legs214to be compactly folded together for transportation of the support apparatus.

Ball joint218allows vertical and horizontal movement of strobe body220so that strobe lamp reflector and lens222can be directed towards the subject, regardless of the position of strobe assembly215along its associated leg214. For example, if strobe assembly215is positioned near the bottom of its associated leg214, then strobe body220should be pointed at an angle close to the horizontal plane. If strobe assembly215is positioned near the top of its associated leg214, then strobe body220should be rotated closer to vertical.

Strobe body220serves to hold a strobe lamp and serves as a mounting point for strobe lamp reflector and lens assembly222. Strobe lamp and reflector and lens assembly222provides an even field of illumination over the photograph area.

FIG. 3shows a side view of a mobile strobe light slidably coupled to a leg306in accordance with one embodiment of the present invention. A self-propelled mobile assembly302is capable of linear motion along the length of leg306. The position of mobile assembly302is sensed by position sensor304. Coupling310allows strobe light308to rotate in the vertical plane. The rotational motion of strobe light308is motorized and can be controlled independently of the motion of self-propelled mobile assembly302.

Self-propelled mobile assembly302allows strobe light308to be automatically positioned along the length of leg306. Self-positioning of the strobe light is advantageous in that it saves time when collecting a large number of images and it assures accuracy in positioning strobe light308. Speed and accuracy are very important factors in the collection of forensic evidence.

An internal motor propels mobile assembly302. A typical motor for this type of application is a stepper motor. Instead of spinning continuously, the stepper motor rotates in small increments or steps and is often used in printers and plotters where there is much start-stop motion and accurate positioning is required. Power to the motor can be supplied via insulated rails303to a brush assembly inside mobile assembly302. Commands to the motor can be supplied via a similar third rail305. To facilitate compaction of the support apparatus, mobile assembly302is removable from leg306.

As previously described, it is desirable that the position of the strobe light be known for each image in the polynomial texture mapping data set. Position sensor304determines the position of mobile assembly302along leg306. Position along the leg can be encoded in a variety of ways including an optical Gray code, optical bar code, or mechanical detents sensed with micro switches. Optically sensed Gray codes are often used to convey positional information in mechanical devices. A Gray code is attractive for use in position sensing because there is no chance for a single bit error to introduce ambiguity as the code changes between adjacent positions. This is because the code is fashioned so that there is only a single bit change between all adjacent positions. For example, if a binary code were used to encode position, changing from position-15to position-16would cause five bits in the code to change state. If the mobile assembly stopped between position-15and position-16there is a chance that all of the bits would not change state and that an erroneous position would be reported. In such a case, a Gray code would report either position-15or position-16and no other. The aforementioned third rail can also be used to return position data to a central sequencer and controller.

As the position of mobile assembly302changes, the angle between the subject and strobe light308also changes. It is desirable that strobe light308point directly at the subject, regardless of the position of mobile assembly302. To facilitate this, strobe light308is rotatably coupled to mobile assembly302through a motorized coupling310. Using a stepper motor similar to that of mobile assembly302, the angle of the strobe light can be varied according to the position of the mobile assembly along the length of the leg306. In this manner, strobe light308can remain aimed directly at the subject, regardless of its position along the leg.

FIG. 4Adepicts a typical strobe light firing sequence in accordance with one embodiment of the present invention. As previously described, the firing of a strobe light results in the formation of a single image for the multi-image polynomial texture mapping data set. The six depictions402,404,406,408,410, and412show a single support apparatus with six strobe lights, two of which are mounted to each leg. In each of the six depictions402,404,406,408,410, and412a single strobe light is shown firing. For example, in depiction402, the top strobe light on the left leg of the support apparatus is shown firing. In depiction404, the top strobe light on the center leg of the support apparatus is shown firing. In total, the sequence of strobe light firings results in the creation of six data images.

FIG. 4Bdepicts a typical strobe light firing sequencer414in accordance with one embodiment of the present invention. The sequencer414is connected to a set of strobe lights416and a camera418. In this example, there are six strobe lights. The sequencer414can be programmed to fire the individual strobe lights in any order. After each strobe light is fired, the camera418is advanced in preparation for the next photograph.

FIG. 5is a flowchart diagram of the operations for obtaining a set of digital photographs500with manually positioned strobe lights to be used with polynomial texture mapping, in accordance with one embodiment of the present invention. As previously described, polynomial texture mapping is a digital image processing technique that relies on having a number of images of the subject object. For each of the images, the camera and subject remain in the same position and the position of the lighting changes.

First, the support apparatus is placed with the camera substantially normal to the subject (502). If the camera has a zoom lens, then the focal length of the lens is adjusted to optimally frame the subject. The camera lens is then focused and the optimum lens aperture is determined and set.

Next, the strobe lights are positioned at the first detent positions (504) along the length of the legs. Rather than having a separate strobe light at every lighting position, the support apparatus can be made lighter and more portable by having only one to several strobe lights per leg. Moving the strobe lights to different positions along the length of the leg allows a multiplicity of images to be obtained using as few as one strobe light per leg.

The strobe sequencer is now set to select the first strobe light (506). The sequencer controls the camera and the sequential firing of the strobe lights. The sequencer can be either automatic or manual. Before the first exposure is made, the light-shielding screens can be attached to the support apparatus as needed to block ambient light from the photographs.

With the support apparatus now in position, the camera focused, the strobe lights positioned, and the sequencer set, the first sequence of photographs can now be taken. A “sequence” refers to a set of photographs with the strobe lights at a given position. Typically, multiple sequences are used to collect a set of images used for a single polynomial texture mapping analysis.

Firing the strobe light while exposing the photograph (508) captures an image. Typically, a single strobe-lit photograph comprises the following steps. Upon receiving a signal from the sequencer, the camera lens diaphragm closes to its predetermined opening and the camera shutter opens. The strobe light is then fired. A built-in exposure sensor in the camera determines the length of the strobe light flash. After the strobe light is extinguished, the shutter is closed and the captured image is stored in the camera's memory.

The sequencer then determines if the photographic sequence is complete (510). If the sequence is not complete, then the sequencer advances the camera and the next strobe light in the sequence is selected (512). A new photograph is then taken as before in (508). If the sequence is complete, then it is decided if an additional photograph sequence is desired (514).

If an additional photograph sequence is desired, then the strobe lights are positioned at the next detent positions (516). The sequencer is then set to select the first strobe light (506) and then the sequence of photographs is taken as before. If an additional photograph sequence is not desired, then the process is done (518).

FIG. 6is a flowchart diagram of the operations for obtaining a set of digital photographs600with automatically positioned strobe lights to be used with polynomial texture mapping, in accordance with one embodiment of the present invention. As previously described, polynomial texture mapping is a digital image processing technique that relies on having a number of images of the subject object. For each of the images, the camera and subject remain in the same position and the position of the lighting changes.

First, the support apparatus is placed with the camera substantially normal to the subject (602). If the camera has a zoom lens, then the focal length of the lens is adjusted to optimally frame the subject. The camera lens is then focused and the optimum lens aperture is determined and set.

As with the support apparatus inFIG. 5having manually positioned strobe lights, the support apparatus can be made lighter and more portable by having only one automatically positioned strobe light per leg rather than having a separate strobe light at every lighting position. Automatically moving the single strobe light to different positions along the length of the leg allows a multiplicity of images to be rapidly obtained.

Next, the sequencer receives a parameter specifying the number of photograph sequences (604) to be made. Based upon the number of photograph sequences needed, the first and final strobe light positions along with any required intermediate positions can be calculated (606). In one embodiment, constant linear displacement of the strobe light along the leg translates into variable linear angular elevation change of the strobe light with respect to the subject. For constant angular change between sequences, an alternate embodiment calculates separate linear displacements. This calculation varies with the total number of sequences desired. After calculating the strobe light positions, the strobe lights are moved to their first positions (608).

The strobe light sequencer is now set to select the first strobe light (610). The sequencer controls the camera and the sequential firing of the strobe lights. The sequencer is automatic. The light-shielding screens can be attached as needed to the support apparatus to block ambient light from the photographs before the first exposure is made.

Firing the strobe light while the camera lens is open (612) captures an image. As previously described, typically, a single strobe-lit photograph comprises the following steps. Upon receiving a signal from the sequencer, the camera lens diaphragm closes to its predetermined opening and the camera shutter opens. The strobe light is then fired. A built-in exposure sensor in the camera determines the length of the strobe flash. After the strobe light is extinguished, the shutter is closed and the captured image is stored in the camera's memory.

The sequencer then determines if the photographic sequence is complete (614). If the sequence is not complete, then the sequencer advances (616) the camera and the next strobe light in the sequence is selected. A new photograph is then taken as before in (612). If the sequence is complete, then it is decided if the strobe lights are at their final positions (618).

If the strobe lights are not at their final positions, then the strobe lights move to the next position (620). The sequencer is then set to select the first strobe light (610) and then the sequence of photographs is taken as before. If the strobe lights are at their final positions, then the process is done (622).

While specific embodiments have been described herein for the purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. For example, figures and descriptions above reference using embodiments of the present invention with polynomial texture mapping image process operation, however alternate embodiments of the present invention can be readily adapted for use with other image processing operation including, for example, shape from shading and others. These image-processing operations also would benefit by the portability of the present invention and the flexibility of positioning the lights and camera. Further, figures and descriptions also reference using a tripod having three support legs however, alternate embodiments contemplate using greater or fewer legs and support for the apparatus or to provide additional azimuthal angles for mounting strobe lights. These additional legs can be used for support or purely for additional azimuthal positions. Accordingly, the invention is not limited to the above-described embodiments, but instead is defined by the appended claims in light of their full scope of equivalents.