Abstract:
The invention relates to an image processing device ( 1, 48, 51 ) including: several image signal inputs ( 2 - 9 ) for receiving a respective image input signal, the signals being unsynchronized; at least one image signal output ( 23 - 26 ) for emitting at least one image output signal; a combiner ( 22 ) for combining the different image input signals to form the image output signal; several synchronizers ( 14 - 21 ), which are respectively connected downstream of the image signal inputs ( 2 - 9 ) and which synchronize the unsynchronized image input signals; and several distorters or rectifiers for distorting or rectifying the individual image input signals before they are combined to form the image output signal. According to the invention, the distorters or rectifiers are formed by the individual synchronizers ( 14 - 21 ) and the image input signals are distorted or rectified independently of one another by one or more synchronizers ( 14 - 21 ). The invention also relates to an associated operating method.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an image processing device and to an associated operating method. 
     In video systems and digital graphics systems, often different graphics signals have to be combined with one another to form a single graphics signal. This is the case for example when an object has been recorded in front of a so-called blue screen and must subsequently be blended into a background image, which has been recorded separately and is provided as a separate graphics signal. 
     Furthermore, it is known to perform geometry correction when combining a plurality of different graphics signals. This may be useful for example when the combined graphics signal is projected onto a curved projection surface or else in order to compensate any optical errors of the visualization device. In order to prevent a distorted image impression, the combined graphics signal may then be distorted in order to compensate the curvature of the projection surface. 
     It is also known to perform brightness or color correction when projecting or displaying graphics signals. This is useful for example when a plurality of projectors or screens is to generate a uniform overall image. In order to prevent different color rendering, the graphics signals may be distorted in terms of their color or brightness values so as to compensate any differences between the visualization devices. 
     However, one disadvantage of the known graphics systems for combining different graphics signals is the fact that they receive synchronized graphics signals on the input side. In practice, however, the graphics signals to be combined with one another are often asynchronous, which makes it more difficult to combine them using the known graphics systems or requires specially synchronized graphics systems. 
     Ulrich Schmidt: “Professionelle Videotechnik”, Springer-Verlag (2000), page 483, FIG. 8.71 discloses an image processing device, which can receive different, unsynchronized image input signals on the input side and only then synchronizes them, whereupon the synchronized image input signals are then combined by means of a combiner to form an image output signal. This known image processing device therefore advantageously makes it possible to combine unsynchronized image input signals. 
     The use of so-called frame synchronizers for synchronizing unsynchronized image input signals is also known for example from “Ausbildungshandbuch audiovisuelle Medienberufe”, Vol. 2, Hüthig-Verlag (2003), Section 4.2.1.14, pages 360-361. 
     Further image processing devices are known from:
         Shawky, M.; Bonnet, S.; Favad, S.; Crubille, P.: “A Computing Platform and its Tools for Feature Extraction from On-Vehicle Image Sequences”, IEEE Intelligent Transportation Systems Conference, 2000, Dearborn, Mich., USA, 1-3 Oct. 2000, Conference Proceedings, pp. 39-45.   DE 103 14 105 A1   DD 228 136 A1   LYNX Technik AG: “Series 3000 MiniModules. Product Catalog”, company publication, S3000MM Ver 1.0., Weiterstadt: LYNX, 2003   LI, Kai; CHEN, Han; CHEN, Yuqun et al.: “Building and Using a Scalable Display Wall System”, IEEE Computer Graphics and Applications, Vol. 20, No. 4, July/August 2000, pp. 29-37.   ALLARD, Jeremie; GOURANTON, Valerie; LECOINTRE, Loick et al.: “Neff Juggler and SoftGenLock: Running VR Juggler with Active Stereo and Multiple Displays on a Commodity Computer Cluster”, IEEE Virtual Reality Conference 2002, VR&#39;02, Orlando, Fla., USA, 24-28 Mar. 2002.       

     However, one disadvantage with the above-described known image processing devices is the unsatisfactory image quality when a plurality of unsynchronized image input signals are combined with one another and then geometrically distorted or rectified. 
     The task of the invention is therefore to provide an image processing device and an associated operating method which gives an improved image quality when combining a plurality of image input signals and carrying out geometric distortion or rectification. 
     This task is solved by the features of the invention. 
     SUMMARY OF THE INVENTION 
     The invention comprises an image processing device comprising a plurality of image signal inputs for receiving a respective image input signal, wherein the individual image input signals usually represent an image or a sequence of images. 
     The invention is not restricted to a specific number of image signal inputs, but the image processing device according to the invention preferably has eight image signal inputs so that a total of eight different image input signals can be received. However, the invention can also be implemented with a different number of image signal inputs, for example with two, four, six or more image signal inputs. 
     Furthermore, the image processing device according to the invention preferably has at least one image signal output for outputting an image output signal, wherein the image output signal usually represents an image or a sequence of images. 
     With regard to the number of image signal outputs, the invention is also not restricted to a single image signal output. Rather, it is also possible to provide a plurality of image signal outputs so as to output a corresponding number of image output signals. The individual image output signals may in this case represent different images or sequences of images. Furthermore, it is also possible that the different image signal outputs output image output signals in different data formats, wherein the different image output signals may then represent the same image or the same sequence of images. It is, e.g., possible that one image signal output outputs a digital image output signal, whereas another image signal output of the image processing device according to the invention outputs an analogue image output signal. 
     Furthermore, the image processing device according to the invention preferably comprises a combiner for combining the different image input signals with one another to form the image output signal or to form the individual image output signals. 
     The image processing device according to the invention makes it possible to receive unsynchronized image input signals, so that a synchronizer is respectively connected downstream of the individual image signal inputs, which synchronizer synchronizes the unsynchronized image input signals for the subsequent combining operation. 
     The combiner of the image processing device according to the invention preferably includes a programmable or configurable combinational circuit, which combines the different image input signals with one another in accordance with predefined (preferably variable) programming to form the image output signal and which can be programmed or configured via a serial and/or parallel programming interface. The combining of the different image input signals can therefore be set at the pixel level by means of corresponding programming of the programmable combinational circuit, so that any combinations of the image input signals received on the input side are possible. 
     The programmable combinational circuit for combining the different image input signals preferably has an FPGA (Field Programmable Gate Array), but it is in principle also possible that the combiner in the image processing device according to the invention has a PLD (Programmable Logic Device) or a PAL (Programmable Array Logic). For example, an FPGA available from the company XILINX may be used as the combiner, although the invention is not restricted to this type of FPGA as combiner. Nevertheless, the use of FPGAs of the Virtex II Pro X or Virtex IV type from the company XILINX is particularly advantageous. 
     The combiner of the image processing device according to the invention is preferably connected to a random access memory, the content of which defines the combination of the image input signals. This may be for example a DDR-RAM which may have for example a storage capacity of 128 MBit. 
     Within the context of the invention, it is also possible that the combiner is connected to a read-only memory which contains a start configuration for the combiner, wherein the start configuration is loaded into the combiner at the time of switch-on. This read-only memory may be for example a JTAG Flash memory, but the invention is not restricted to this type of memory with regard to the type of memory for the read-only memory for storing the start configuration. 
     In one preferred example of embodiment of the invention, the image processing device has at least one signal splitter which is connected on the input side to at least one of the image signal inputs and on the output side to at least two of the synchronizers, wherein the signal splitter splits the image input signal applied on the input side between the synchronizers connected to the signal splitter on the output side. This splitting of an image input signal between a plurality of synchronizers may be useful in order to circumvent bandwidth limitations of the synchronizers and to process image input signals with very high bandwidth requirements, as a plurality of synchronizers jointly synchronize and distort one image input signal, wherein the synchronized subsignals are then appropriately recombined by the combiner. In the preferred example of embodiment, the signal splitter receives a respective image input signal on the input side and splits it between two synchronizers, where said signal is synchronized and corrected. However, the invention is not restricted to a splitting ratio of 1:2 but rather can also be implemented with other splitting ratios, for example a splitting ratio of 1:3, 1:4 or more, if the bandwidth limitation of the synchronizers and the bandwidth of the image input signals make this necessary. 
     The signal splitters can preferably be programmed so as, depending on the programming, either to feed each image input signal to a respective one of the synchronizers or to split the individual image input signals in each case between a plurality of the synchronizers. In this case, the image processing device according to the invention therefore has at least two operating modes, wherein the signal splitters are inactive in one operating mode and are switched to the active state in another operating mode in order to split the respective individual image input signals between a plurality of the synchronizers. 
     Preferably, a signal splitter is connected downstream of respective pairs of individual image signal inputs, wherein the individual signal splitters can preferably be programmed individually. It is then possible that one signal splitter of the image processing device according to the invention is switched to the inactive state while another signal splitter of the image processing device according to the invention is switched to the active state. 
     It should furthermore be mentioned that the image processing device according to the invention preferably comprises a central clock generator which is connected on the output side to all the synchronizers. This makes it possible for the individual image input signals to be synchronized by the individual synchronizers independently of their frequency and resolution, so that the signals provided at the outputs of the synchronizers are synchronized down to pixel level. 
     The image processing device according to the invention may further comprise an external synchronization terminal for synchronizing the image processing device with other image processing devices. 
     The image processing device according to the invention further includes at least one distorter or rectifier for respectively individually distorting or rectifying the individual image input signals before they are combined to form the image output signal. Here, the distorter or rectifier is formed by the individual synchronizers, which therefore have two functions, namely on the one hand the synchronization of the image input signals and on the other hand the distortion or rectification thereof. This is provided for example by the chip type sxT1 from the company Silicon Optix, which also has the name “Reon”. However, with regard to the synchronization, the invention is not restricted to chips of this type but rather can also in principle be implemented with other types of chip. However, the synchronizers are preferably bifunctional in that they allow not only the synchronization of the input signals but also the distortion or rectification thereof. 
     The modules referred to as synchronizers within the context of this description may also be referred to as correction modules due to the fact that they are bifunctional, wherein the correction modules or synchronizers offer the following advantages. 
     Firstly, the grouping-together of a plurality of correction modules or synchronizers by using a single clock generator allows the synchronization of different inputs. Secondly, each correction module or synchronizer can correct different resolutions or clock rates of the image signal inputs, so that a uniform image signal is output at the output of each correction module or synchronizer and is passed on to the combiner. 
     Furthermore, the individual correction modules or synchronizers can correct the respective image signal individually with regard to geometry and/or brightness and/or color. 
     Finally, the individual correction modules or synchronizers can individually chop and change the size of (enlarge and reduce) the respective image signal, as a result of which just part of the respective image signal is passed on to the combiner. 
     The term “distortion or rectification” of image signals which is used within the context of the invention is therefore meant in the geometrical sense and not in the telecommunications sense and encompasses, in addition to the geometric correction of the image content, also the correction of the brightness and of the color information. 
     It should also be mentioned that the individual synchronizers preferably in each case have a control input, via which a change of image can be triggered, wherein the control inputs of the individual synchronizers are preferably jointly connected to the combiner in order to receive a common trigger signal from the combiner. This joint triggering of the individual synchronizers by the combiner permits a synchronous change of image, which is usually a prerequisite for the subsequent combining operation. 
     Moreover, the individual synchronizers can preferably be configured via a respective configuration input, wherein the individual configuration inputs of the synchronizers are connected to the combiner via a multiplexer. The combiner can in this case address and configure all the synchronizers via the multiplexer. 
     It should also be mentioned that the image processing device according to the invention is preferably integrated on a single chip or at least on a single printed circuit board. 
     Furthermore, the image signal output of the image processing device may be connected to an image display device, such as a projector or a monitor for example. 
     One advantageous field of application of the image processing device according to the invention consists in the split image calculation in a plurality of nodes of a graphics cluster, if the calculation capacity of the individual nodes alone is not sufficient. Here, the image calculation is split between a plurality of graphics computers such that each processes just part of the image. The coordination of this parallel image calculation may be carried out for example by a control computer. The subsignals processed by the individual graphics computers are then fed to the image signal inputs of the image processing device according to the invention, synchronized and subsequently recombined. 
     The invention also comprises an operating method for an image processing device according to the invention, as is already clear from the above description. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       Other advantageous further developments of the invention are characterized in the dependent claims or will be explained in more detail below together with the description of the preferred examples of embodiments of the invention which is given with reference to the figures, in which: 
         FIG. 1  shows a simplified block diagram of an image processing device according to the invention for combining eight image input signals to form four image output signals, 
         FIG. 2  shows the signal splitter of the image processing device of  FIG. 1 , 
         FIG. 3  shows a more detailed block diagram of part of the image processing device of  FIG. 1 , 
         FIG. 4  shows a graphics system according to the invention comprising a graphics cluster for the parallel processing of graphics signals, 
         FIG. 5  shows a graphics system for projecting image signals, 
         FIG. 6  shows a simplified block diagram of an image processing system according to the invention comprising a plurality of graphics computers as image signal sources and the image processing device according to the invention for combining these image input signals, and 
         FIGS. 7A ,  7 B show a timing diagram which illustrates the rough synchronization of the image input signals in the graphics computers of the image processing system shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The simplified block diagram in  FIG. 1  shows an example of embodiment of an image processing device  1  according to the invention for combining eight unsynchronized image input signals Video In  1 , . . . , Video In  8  to form four image output signals Video Out  1 , . . . , Video Out  4 . 
     In order to receive the individual unsynchronized image input signals Video In  1 , . . . , Video In  8 , the image processing device  1  has a plurality of digital input interfaces  2 - 9  (DVI-D: Digital Video Interface). Here, the individual pixel information items are in each case transmitted in the form of an 8-bit value, wherein the image value for the primary colors red, yellow and blue are transmitted in parallel for each pixel. 
     The individual input interfaces  2 - 9  are in each case connected in pairs on the output side to a plurality of signal splitters  10 - 13 , the structure of which is shown in more detail in  FIG. 2  and will be described in more detail below. 
     On the output side, the individual signal splitters  10 - 13  are connected to eight synchronizers  14 - 21 , which in each case receive two image signals from the individual signal splitters  10 - 13  and synchronize said signals. In this example of embodiment, the synchronizers  14 - 21  are chips of the type sxT1 from the company Silicon Optix, which are also referred to as “Reon”. 
     The image signals synchronized by the synchronizers  14 - 21  are then fed to a combiner  22 , which is an FPGA (Field Programmable Gate Array) of the type Virtex-II from the company XILINX. The combiner  22  combines the image signals received on the input side in accordance with predefined programming (not shown here) to form the image output signals Video Out  1 , . . . , Video Out  4 , and outputs these signals at a plurality of output interfaces  23 - 26 . 
     The image processing device  1  further has a parallel interface  27  and a serial interface  28  for configuring the image processing device  1 . 
     The image processing device  1  also has a central clock generator  29  which is connected on the output side to the synchronizers  14 - 21 . This common clocking of the individual synchronizers  14 - 21  makes it possible for the image input signals Video In  1 , . . . , Video In  8  to be synchronized independently of their frequency and resolution, so that the signals provided at the outputs of the synchronizers  14 - 21  are synchronized down to pixel level. 
     Furthermore, the combiner  22  is connected to the individual synchronizers  14 - 21  via a multiplexer  30 , so as to configure the synchronizers individually. 
     Moreover, the combiner  22  is connected to the individual signal splitters  10 - 13  in order to be able to switch them between two operating modes. In one operating mode, the signal splitters  10 - 13  are inactive, so that the two respective image input signals applied on the input side are switched through to the associated synchronizers. On the other hand, in another operating mode, the signal splitters  10 - 13  are switched to the active state, so that only the image input signal applied to one of the two signal inputs is split between the two synchronizers connected on the output side. In this operating mode, it is also possible to process image input signals having a bandwidth greater than the maximum processing bandwidth of the synchronizers  14 - 21 . 
     Hereinbelow, the structure and functioning of the signal splitter  10  will be described in more detail with reference to  FIG. 2 , wherein the other signal splitters  11 - 13  have the same structure. 
     On the input side, the signal splitter  10  has two TMDS receivers  31 ,  32  which are connected on the input side to the two input interfaces  2 ,  3  and generate an RGB signal having a width of 48 bits. 
     The TMDS receiver  32  in one of the two parallel branches can be switched to the inactive state by the combiner  22  via a control line  33  and an inverter  34 , so that the TMDS receiver  32  does not output an image signal. 
     An amplifier  35  is moreover arranged between the two signal processing branches, which amplifier can pass the image signal output by the TMDS receiver  31  to the synchronizer  15  of the other signal processing branch. The amplifier  35  can in this case also be switched to the inactive state by the combiner  22  via the control line  33 , the inverter  34  and a further inverter  36 . The two inverters  34 ,  36  thus ensure that either the TMDS receiver  32  or the amplifier  35  is switched to the active state. This means that, depending on the actuation via the control line  33 , either the two image input signals Video In  1 , Video In  2  received on the input side are passed to the downstream synchronizers  14 ,  15  without any further modification or else only the image input signal Video In  1  received on the input side is split and distributed between the two synchronizers  14 ,  15 . 
     This splitting of the image input signals received on the input side makes it possible to circumvent bandwidth limitations of the synchronizers  14 - 21  and to process image input signals of higher bandwidth. 
     Hereinbelow, the detailed example of embodiment shown in  FIG. 3  will be briefly described, wherein for the sake of simplification just part of the image processing device  1  comprising the input interfaces  2 ,  3  is shown. 
     For the sake of simplification, the same references are used here as in  FIGS. 1 and 2 , wherein reference is largely made to the above description in order to avoid repetitions. 
     It can further be seen from this block diagram that each input interface  2 ,  3  has a respective DDC-EEPROM  37 ,  38  which provides a DDC string. 
     Moreover, each of the synchronizers  14 ,  15  is connected to a random access memory  39 ,  40 , in which the image data are buffer-stored. 
     The combiner  22  is also connected to a memory  41 , in which the start configuration for the combiner  22  is stored, wherein the start configuration is loaded into the combiner  22  from the memory  41  at the time of switch-on. Here, the memory  41  is a JTAG Flash memory. 
     Hereinbelow, the example of embodiment of a graphics system according to the invention which is shown in  FIG. 4  will be described. 
     Here, a plurality of graphics computers  44 - 47  calculates respective image sections of a high-resolution image. A control computer  43  carries out the coordination of the image calculation on the individual graphics computers  44 - 47 . Due to the fact that the image signal to be processed is split in this way between a plurality of graphics computers  44 - 47 , it is possible to achieve a high processing capacity using simple graphics computers. 
     On the output side, the individual graphics computers  44 - 47  are connected to an image processing device  48  according to the invention, which synchronizes and combines the unsynchronized output signals of the individual graphics computers  44 - 47  so that a combined image output signal Video Out is provided at the output of the image processing device  48 . 
     This image output signal Video Out is fed to a projector  49 , which projects an image onto a curved projection surface  50 . The curvature of the projection surface  50  is compensated here by a complementary distortion in the synchronizers of the image processing device  48 , so that the image on the projection surface  50  appears to be undistorted despite the curvature of the projection surface  50 . 
     Hereinbelow, the example of embodiment of a graphics system according to the invention which is shown in  FIG. 5  will be described, in which two image input signals Video In  1 , Video In  2  are fed to an image processing device  51  according to the invention, which geometrically distorts the image input signals Video In  1 , Video In  2  in order to compensate the curvature of a projection surface  52 , and also corrects the brightness and color so as to compensate any differences between the projectors  53 ,  54 . 
     On the output side, the image processing device  51  is connected to two projectors  53 ,  54 , which project the two image output signals Video Out  1 , Video Out  2  onto the projection surface  52 . 
     Here, the two images projected by the projectors  53  and  54  overlap in an overlap area  55  on the projection surface  52 . The image processing device makes it possible to carry out a brightness correction for the image signals in this area, which permits so-called “edge blending”. 
       FIG. 6  shows a simplified block diagram of an image processing system according to the invention comprising a plurality of graphics computers  60 ,  61 ,  62 ,  63  which each supply an image input signal, wherein the image input signals provided by the graphics computers  60 - 63  are unsynchronized. 
     Furthermore, the illustrated image processing system has an image processing device  64  according to the invention comprising a plurality of image signal inputs  65 - 72  and a plurality of image signal outputs  73 - 76 . The image signal inputs  65 - 72  are supplied with the unsynchronized image input signals from the graphics computers  60 - 63 . 
     A respective so-called WARP chip  77 - 84  is connected downstream of the individual image signal inputs  65 - 72  in the image processing device  64 , wherein said chip is in each case essentially a synchronizer which synchronizes the unsynchronized image input signals received on the input side with one another. 
     On the output side, the WARP chips  77 - 84  are connected to a combiner  85  in the form of an FPGA. 
     The combiner  85  is in turn connected on the output side to the image signal outputs  73 - 76  via a plurality of TMDS transmitters  86 - 89 . 
     Furthermore, the image processing device  64  in this example of embodiment also has a plurality of analogue output interfaces  90 - 93 . 
     However, it is particularly important here that the phase difference between the image input signals received from the graphics computers  60 - 63  is determined in the image processing device  64  and coupled back to the graphics computers  60 - 63  via an interface  94 . The graphics computers  60 - 63  then carry out rough synchronization of the image input signals fed into the image processing device  64 , so that the image processing device  64  then has to perform only fine synchronization of the image input signals. 
     The image processing device  64  has a possibility for synchronization which can synchronize the image signals down to the pixel level (“GENLOCK”), so that the image input signals received via the image signal inputs  65 - 72  need not be provided in a synchronous manner down to the pixel level. However, in order to keep the latency of the image processing device  64  as low as possible, it is useful if the image input signals are provided in a manner such that they are already roughly synchronized. The only important thing here is that the time of the respective image start (“FRAMESYNC”) is phase-shifted by no more than 5-10° relative to the other image input signals (“FRAMELOCK”). The exact synchronization of the image input signals (“GENLOCK”) is then carried out by the WARP chips  77 - 84  of the image processing device  64 . 
     The rough synchronization of the image input signals fed into the image processing device  64  may be implemented in the graphics computers  60 - 63  by a software routine which increases or reduces the length of the vertical blanking interval of the image signals, as can be seen from the timing diagrams in  FIGS. 7A and 7B . All that is required for this is the information concerning the actual phase shift of the image input signals, which is provided by the image processing device  64  via the interface  94 . 
     The invention is not restricted to the preferred examples of embodiments described above. Rather, a large number of variants and modifications are possible which likewise make use of the inventive concept and therefore fall within the scope of protection. 
     LIST OF REFERENCES 
     
         
           1  image processing device 
           2 - 9  input interfaces 
           10 - 13  signal splitters 
           14 - 21  synchronizers 
           22  combiner 
           23 - 26  output interfaces 
           27  parallel interface 
           28  serial interface 
           29  clock generator 
           30  multiplexer 
           31  TMDS receiver 
           32  TMDS receiver 
           33  control line 
           34  inverter 
           35  amplifier 
           36  inverter 
           37  DDC-EEPROM 
           38  DDC-EEPROM 
           39  random access memory 
           40  random access memory 
           41  memory 
           42  -- 
           43  control computer 
           44 - 47  graphics computers 
           48  image processing device 
           49  projector 
           50  projection surface 
           51  image processing device 
           52  projection surface 
           53  projector 
           54  projector 
           60 - 63  graphics computers 
           64  image processing device 
           65 - 72  image signal inputs 
           73 - 76  image signal outputs 
           77 - 84  WARP chips 
           85  combiner 
           86 - 89  TMDS transmitters 
           90 - 93  analogue interfaces 
           94  interface 
         VIDEO IN  1 , . . . , 
         VIDEO IN  8  video input signals 
         VIDEO OUT  1 , . . . , 
         VIDEO OUT  4  video output signals 
         Video  1 , . . . , 
         Video  4  video signals