Abstract:
A method of processing a rectangular image for display on a curved screen. The method warps a real-time image and projects the warped image onto a curved screen without distortion.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image warping method for a curved screen, and more particularly to a real-time image warping method.  
         [0003]     2. Description of the Related Art  
         [0004]     In a conventionally virtual reality system, a screen surrounds users to provide an immersion effect. Joint seams occur when a combined image is formed by many small images projected by different projectors. A curved screen de-emphasizes seams for better immersion effect. Conventional projectors, however, are designed to project images only on a planar screen. If a conventional projector projects images on a curved screen, distortion can negatively affect the virtual experience.  
         [0005]      FIG. 1  shows an exemplary image projected by a projector. When the projector projects an image  20  on a curved screen, a distorted image  22  appears. Distances from the projector to the sides compared to the middle of the screen are different, such that the lower portion of image  22  is distorted.  
         [0006]     Several convention solutions have been developed. In one an image is processed by a warping method and then projected onto a curved screen. Such warping methods require numerous CPU operations if implemented by software. This solution is inexpensive but processing speed is low. Thus, it is best suited to process predictable images, such as those previously recorded. Real-time image displays, however, responding to random movement of a subject, are beyond the capability of this solution.  
         [0007]     Warping performed by hardware with accelerated process speed while addressing those shortcomings is costly and increases maintenance requirements.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, an object of the present invention is to provide a simplified method of image warping, thereby increased processing speed, and decreasing cost and inconvenience.  
         [0009]     The invention provides a method of processing a rectangular image for display on a curved screen by the following steps. First, a first plane region is defined in an image frame of a projector to display the rectangular image. The first plane region comprises first and second rectilinear boundaries parallel to each other. The first rectilinear boundary has first and second ends. Next, a curve is generated according to user input and passes through the first and second ends. Thereafter, a second plane region is defined in the image frame with the curve and the second rectilinear boundary as two boundaries. The rectangular image is warped to fit substantially the second plane region for projection onto the curved screen. Finally, the warped image is projected.  
         [0010]     The first rectilinear boundary has a length of W. The rectangular image has a bottom pixel displayed on the first rectilinear boundary a distance of x away from the center of the first rectilinear boundary. The radius of the curve is R. The bottom pixel is moved forward to the second rectilinear boundary by a distance of  
             R   2     -     x   2         -           R   2     -       (     W   2     )     2         .         
 
         [0011]     The invention also provides a method for displaying a large-angle image onto a curved screen. The large-angle image comprises rectangular images. First, a curved screen is split into a plurality of regions. Thereafter, each rectangular image is warped to substantially fit into a corresponding region. Finally, each warped image is projected onto its corresponding region. The resulting projected image has a portion overlapping with a neighboring projected image. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention can be more fully understood by reading the subsequent detailed description and examples with reference made to the accompanying drawings, wherein:  
         [0013]      FIG. 1  shows an exemplary image projected by a projector;  
         [0014]      FIG. 2   a  shows the method of processing a rectangular image of the present invention;  
         [0015]      FIG. 2   b  shows the principle of the warping method of the present invention;  
         [0016]      FIGS. 3   a  to  3   c  show the warping method of the present invention;  
         [0017]      FIG. 4  shows an exemplary compressed image in a newly created area;  
         [0018]      FIG. 5  shows another exemplary compressed image in the newly created area;  
         [0019]      FIGS. 6   a  to  6   c  show steps of generating the curve defining the newly created area;  
         [0020]      FIG. 7  shows another embodiment of the present invention;  
         [0021]      FIG. 8  shows a warped image according to the present invention;  
         [0022]      FIGS. 9   a  to  9   b  show the display method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 2   a  shows the method of processing a rectangular image of the present invention. Original image  30  is normally rectangular is disposed in an image frame in a projector. Currently projects normally use LCDs for receiving image frames thereon for projection. Before projection, the image  30  is warped, resulting in warped image  32 , which is the projected onto a curved screen generating undistorted projection image  34 .  
         [0024]      FIG. 2   b  shows the principle for image warping of the present invention. The area in the image frame is occupied by the image  30 , defined as a rectangular zone with a top rectilinear boundary and a bottom rectilinear boundary. The bottom rectilinear boundary has two ends, POINT 1  and POINT 2 . Curve ARC 1 , passing POINT 1  and POINT 2 , is thus defined. The center of Curve ARC 1  is located on a perpendicular bisector of the bottom rectilinear boundary. Another area is defined by the ARC 1 , two vertical side walls and the top rectilinear boundary, into which a warped image  32  substantially fits. The definition method for ARC 1 , is described here after. The image  30  is segmented into vertical sections, each compressed according to a shortened length defined by ARC 1 . By combining sections, the compressed the warped image  32  is created and projected to corresponding to the rectangularity of the original image.  
         [0025]     In  FIG. 2   b , a circle has a radius of R and a circumference passing through POINT 1  and POINT 2  with a distance between point C and the center of the bottom rectilinear boundary of x. The vertical distance between ARC 1 , a segment of the circle, and point C can be derived by Equation 1:  
             R   2     -     x   2         -         R   2     -       (     W   2     )     2             
 
         [0026]     A digital content creator (DCC) processing the warping method of the present invention in a projector or computer generates image  30 , a rectangular image, fitting the newly created area in the image frame enclosed by ARC 1 , two vertical side walls and the top rectilinear boundary. The bottom pixels of image  30  displayed at the bottom rectilinear boundary are moved by the DCC forward to the top rectilinear boundary according to the distance obtained from Equation 1. Since the DCC executes the warping method of the present invention in a processing device of the projector or a display card of the computer, the executing time of the DCC is short. All pixels in image  30  are also moved into the newly created area to generate warped image  32 .  
         [0027]      FIGS. 3   a  to  3   c  show the warping method of the present invention. First, in  FIG. 3   a , a plane region REG 1  in an image frame of a projector is defined to display an image  30 . The plane region REG 1  has a top rectilinear boundary and a bottom rectilinear boundary, parallel to each other.  
         [0028]     Next, as shown in  FIG. 3   b , a control panel of a projector or a connected computer allows a point on the bottom rectilinear boundary to be dragged define ARC 1  passing through POINT 1  and POINT 2 .  
         [0029]     As shown in  FIG. 3   c , a newly created area REG 2  in the image frame is defined by ARC 1 , two vertical side walls and the top rectilinear boundary LINE 1 . In  FIG. 3   c , the pixels on the bottom rectilinear boundary are moved forward by the DCC to ARC 1 . Furthermore, the pixels in image  30  are also moved by the DCC into the newly created area to generate warped image  32 .  
         [0030]      FIG. 4  shows an exemplary compressed image fitting the new created area. In  FIG. 4 , normal 1  to normal m  are perpendicular to the bottom rectilinear boundary LINE 1 . An original image is vertically split into columns sections, each only on a corresponding normal, consisting of pixels on the corresponding normal, thus defined as column pixels. Compression of a column section moves column pixels by the DCC along the corresponding normal and forward to the bottom rectilinear boundary LINE 1 . The distance moved of a column pixel depends on the location of the corresponding normal and the gap on the normal between the curve ARC 1  and the bottom rectilinear boundary LINE 1 . In this way, column pixels in a column section are separated by the same distance, near each other, stay on the same normal and relocate into the newly created area.  FIG. 4  shows a result. PIX (1,0) ˜PIX (1,n)  is on normal 1  and PIX (2,0) ˜PIX (2,n)  is on normal 2 . Furthermore, bottom pixels PIX (1,0)  and PIX (2,0)  are relocated to ARC 1 . In  FIG. 4 , each bottom pixel is moved a distance according to Equation 1, resulting in precise positioning. Perfect fitting is the benefit of this embodiment.  
         [0031]      FIG. 5  shows another exemplary compressed image substantially fitting into the new created area. Rather than covering only one normal in  FIG. 4 , in  FIG. 5 , each column section covers  3  corresponding normals, comprising corresponding column pixels thereon. Thus, an original image is vertically split into column sections, each rectangular with a top line TS m  and a bottom line TB m  and having lines of column pixels. The pixels with the same vertical height in the same column strip are moved by the DCC by the same distance to maintain a horizontal line. It is shown in  FIG. 5  that a bottom line TB m  of a compressed column section is substantially located on or across curve ARC 1 , in order to fit the compressed image into the newly created area enclosed by curve ARC 1 , the top rectilinear boundary LINE 2  and two vertical side walls.  
         [0032]      FIGS. 6   a  to  6   c  show steps of creating the curve to define the new created area. First, in  FIG. 6   a , a point POINT 3  at the center of the bottom rectilinear boundary LINE 1  is defined by the DCC as adjustable or moveable along a perpendicular bisector MID 1  of LINE 1 . By moving POINT 3  along MID 1 , ARC 1 , which passes through POINT 1 , POINT 2 , and the moved POINT 3 , can be defined and generated, with a primary newly created area accordingly defined, as shown in  FIG. 6   b . The distance between the adjustment point POINT 3  and the bottom rectilinear boundary LINE 1  thus becomes an adjustment parameter for the radian of the curve ARC 1 . If the curvature of the primary new created area is insufficient for a warped image to appear undistorted, another fine-tuning step is introduced. In  FIG. 6   c , on ARC 1 , points FP 1 , FP 2 , . . . , FP 1  are selected as fine-tunable points, while the location of POINT 3  is fixed. Moving any of the fine-tunable points generates movement of adjacent points to alter the curvature of ARC 1  by the DCC, thereby passing through all the fine tunable points. As shown in  FIG. 6   c , when FP 1  remains in the same place, FP 2  and FP 3  move slightly, ARC 1  is fine-tuned and is no longer a portion of a circle. By way of the fined-tuned ARC 1 , another created area is defined and an image can be warped accordingly to be shown on a curved screen undistorted.  
         [0033]     In addition to application to the bottom rectilinear boundary, the method of defining a curve can also be applied to the top rectilinear boundary. A curve ARC 2  is defined as shown in  FIG. 7 . The curve ARC 2  is defined by a control panel of the projector or the connected computer and passing two ends POINT 4  and POINT 5 . Another area is defined in the image frame by the curves ARC 1  and curve ARC 2  and two vertical side walls. The image  30  is segmented into several vertical sections by the DCC and compressed according to a shortened length defined by curves ARC 1  and ARC 2 . By combining the compressed sections, a warped image shown in  FIG. 8  is created and projected onto a curved screen should be corresponding to the rectangularity of the original image.  
         [0034]      FIG. 9   a  shows images respectively projected from projectors on a single curved screen. For a panoramic or large-angle image, a single projector may not be enough. In  FIG. 9   a , projectors  41 ˜ 46  are provided, with projectors  41  and  42  stacked in a straight line MID 11 , projectors  43  and  44  on MID 12 , and projectors  45  and  46  on MID 13 . The straight line MID 11 , is a perpendicular bisector of REG 11  and REG 21 . The straight line MID 12  is a perpendicular bisector of REG 12  and REG 22 . The straight line MID 13  is a perpendicular bisector of REG 13  and REG 23 .  
         [0035]     The curved screen is split into regions REG 11 ˜REG 23 . Each projector projects a warped image onto the corresponding region of the curved screen. Each warped image can be generated by the method of processing a rectangular image disclosed.  
         [0036]     To avoid image discontinuity or gap between projected images, each the warped image IMAG 11 ˜IMAG 23  is preferably larger than its corresponding region on the curved screen. As shown in  FIG. 9   b , image IMAGL 1  overlaps image IMAG 12  in portion REG c1  and image IMAG 12  with image IMAG 13  in portion REG c2 .  
         [0037]     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.