Abstract:
The present invention utilizes a new and inexpensive method for stereoscopic demultiplexing from a single computer data source. The invention provides a means to switch the routing of left and right image data, if necessary. Additionally the invention provides for an internal swap of the green data signal between the two channels permitting the device to be used with polarized output projection systems in which the green light output is polarized orthogonally to the red and blue light output.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to provisional application No. 60/317,260 filed on Sep. 5, 2001 and is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention is a stereoscopic multiplexer and in particular a stereoscopic multiplexer creating two separate signals from a single source for connecting a stereoscopic image to a dual projector system.  
           [0004]    2. Description of the Related Art  
           [0005]    Stereoscopic image presentation using dual projection systems has been popular in the past for the presentation of 3D video content. Efforts have also been made in the area of projecting stereoscopic data from a computer system using dual-projector 3D displays. In both cases, special stereoscopic image demultiplexing equipment has been required to split 3D content coming from a single source into two separate signals for the dual projector system. Historically stereoscopic image demultiplexers have been expensive and difficult to find. Other alternatives have involved the use of dual sources that must be synchronized. Examples of prior efforts include: a video 3D image demux that converts field sequential stereo to two separate VGA channels made by 3D ImageTek; and a device that converts computer page-flipped stereo into two VGA channels by Cyviz.  
           [0006]    The present invention utilizes a new and potentially inexpensive method for stereoscopic demultiplexing from a single computer data source.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention solves the problem of stereoscopic image demultiplexing from a single computer source by using a novel line-attenuation approach. Stereoscopic image demultiplexer products based on the present invention have the potential to be much more inexpensive than current technologies. There are trade-offs involved in image quality verses cost, however there is a gain in the applicability of the product to existing computer and projection systems.  
           [0008]    A computer system transmits stereoscopic 3D content using the common “row-interleaved” 3D format at any resolution and any vertical refresh rate. The preferred embodiment splits the signal into two channels using a distribution amplifier technology. Since the left-right stereoscopic image information is encoded in the rows of the image, a special circuit is utilized to attenuate or “blank out” the odd rows in one image channel and the even rows in the other image channel. The resulting signals contain only left or right image information that is sent to the appropriate projection system. For example, in one embodiment, image channel A is assigned to pass only the left perspective image data and image channel B is assigned to pass only the right perspective image data. If the left perspective image data is encoded on odd lines and the right perspective image data is encoded on even lines, then the line attenuation circuit will attenuate even lines in image channel A and will attenuate odd lines in image channel B. Since the native computer data signals are analog and since the line attenuation circuit works equally well for either analog or digital signals, a product based on this simple concept can be made very inexpensively since it does not require a costly analog-to-digital conversion step.  
           [0009]    The present invention also provides a means to switch the routing of the left and right image data if necessary. For example, if left image data is being routed to channel A and right image data is being routed to channel be, there are instances when the routing would need to be reversed such that right image data is routed to channel A and left image data is routed to channel B. This function is variously called “field-swap” or “pseudo-stereo swap”.  
           [0010]    An additional embodiment provides for an internal swap of the green data signal between the two channels. This functional permits the device to be used with polarized output projection systems (such as polysilicon based projection systems) in which the green light output is polarized orthogonally to the red and blue light output. This functionality opens up a much broader range of application for products based on the present invention. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other features, aspects, and advantages of the present invention will be become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0012]    [0012]FIG. 1 illustrates a stereoscopic image demultiplexer functional block diagram;  
         [0013]    [0013]FIG. 2 illustrates a distribution amplifier block diagram;  
         [0014]    [0014]FIG. 3 illustrates a schematic diagram of the line attenuation circuit in the preferred embodiment;  
         [0015]    [0015]FIG. 4 illustrates a demux control system block diagram; and  
         [0016]    [0016]FIG. 5 illustrates a green swap system block diagram. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 illustrates a functional block diagram the Stereoscopic Demultiplexer  100  of the present invention. A single RGB computer data signal enters the system from the right. In order to properly direct left and right eye image information to the proper output channel, the input RGB signal must be formatted such that left eye information is present on even (or odd) lines only and right eye information is present on odd (or even respectively) line only. The Distribution Amplifier block  102  splits the single input channel data from the computer  104  into two separate RGB output channels. In the figure R represents the Red color analog data signal, G represents the green data signal, B represents the blue data signal, H represents the horizontal synchronization signal, and V represents the vertical synchronization signal. Both outputs of the distribution amplifier are electrically buffered and terminated separately. However the data in both channels remain mutually synchronized. The function of both Line Attenuator A  106  and Line Attenuator B  108  is to attenuate to black alternate lines of data in channel A and channel B respectively. When the unit is in 3D mode, Line Attenuator A  106  attenuates even (or odd) lines while Line Attenuator B  108  attenuates odd (or even) lines. When the unit is in 2D mode, no lines of data are attenuated in either channel. Attenuation is controlled by the Controller system  110 . Because of the nature of some projection systems (e.g., certain polysilicon projectors), it is necessary to swap the green data signals between channels A and B in order to display 3D stereoscopic images. Therefore the Green Swap System  112  has been included to support those projection systems for which the Green light output has a polarization axis at a different angle than the red and blue light output. Under normal circumstances the Green data signal from Channel A passes straight through to the Channel A output. Likewise the Channel B Green data signal normally passes to the Channel B output  116 . However, when the device is required to run in Green Swap Mode, the Controller commands the Green Swap System to route the Channel A Green data signal to the Channel B Green data output and the Channel B Green data signal to the Channel A Green data output. The Controller system receives input from the User Interface system  112 , interprets the input according to a predefined truth table, and generates the appropriate control signals for Line Attenuator A  106 , Line Attenuator B  108 , and the Green Swap System  112 .  
         [0018]    [0018]FIG. 2 illustrates a functional block diagram of the distribution amplifier  200 . The purpose of the Distribution Amplifier is to split the single RGB computer data input into two separate and electrically independent output channels with identical information. The Input amplifier  202  receives the RGBHV input and is properly terminated for the best quality signal. The output of the input amplifier is routed to two more identical Output Amplifiers  204  and  206 . The Output Amplifiers boost each signal and provide proper 75-ohm termination on the outputs for best signal quality.  
         [0019]    [0019]FIG. 3 illustrates a schematic diagram of the Line Attenuation System  300  of the preferred embodiment. A Line Attenuation Control signal controls the operation of three transistors  302 ,  304 , and  306  whose purpose is to clamp the data line voltage close to zero when the control signal is “high”. The result is a voltage value that represents “black” or “dark gray” on the display. The resistors at the base of each transistor eliminate image ghosting and tear that sometimes occurs when only one or two color channels are transmitting “black” (i.e., low voltage). This represents an improvement in the system presented in previous patent applications.  
         [0020]    An a Itemative to the line attenuation circuit described previously is the analog switch based mechanism shown in FIG. 6. The mechanism  600  shown is based on three analog switch components  608 ,  610  and  612  corresponding to the red, green, and blue color channels respectively. One input of each of the three analog switches is connected to one color channel input. The other input of each of the three analog switches is connected through a termination resistors to system ground  602 ,  604  and  606 . The output of each analog switch is connected to an output color channel. This mechanism functions exactly as the line attenuation block described previously. The analog switch may be implemented using the PIV330Q video multiplexing chip from Pericom or other similar analog switch.  
         [0021]    [0021]FIG. 4 illustrates the functional block diagram of the Demux Control System. In the preferred embodiment this system is implemented using a digital logic circuit that implements the function represented in Table 1. The purpose of the Demux Control System is to interpret user interface signals and the horizontal and vertical synchronization signals to generate the appropriate Line Attenuator and Green Swap system control signals.  
         [0022]    Table 1 is a Demux Control System Line Attenuator Truth Table that illustrates the functionality implemented by the Demux Control System. When the 2D/3D input is 0, the device is to operate in 2D mode. Therefore all other inputs are ignored and the CTRLA and CTRLB outputs are set to 0 to disable line attenuation. When the 2D/3D signal is high, the device is in 3D mode. In this case the FSWAP, Vs, and Hs inputs are no longer ignored. The purpose of the FSWAP input is to switch the lines that are attenuated by each Line Attenuator. For instance, in the preferred embodiment, when the FSWAP input is 0, Line Attenuator A is commanded to attenuate even lines and while Line Attenuator B is commanded to attenuate odd lines. When FSWAP is 1 Line Attenuator A attenuates odd lines and Line Attenuator B attenuates even lines. When the Vs (vertical synchronization input) is 1 (that is the synch signal is active), CTRLA and CTRLB outputs are reset to an initial value that depends on the state of the FSWAP input. In the preferred embodiment, when Vs is 1 and FSWAP is 0, then CTRLA is set to 1 and CTRLB is set to 0. Alternately when Vs is 1 and FSWAP is 1, the CTRLA is set to 0 and CTRLB is set to 1. This functionality ensures that the appropriate lines are attenuated during each frame of image data. Finally, when Vs is 0 (the vertical synchronization signal is not present or active) the state of both CTRLA and CTRLB are toggled with each successive Hs signal pulse. This function identifies the lines that are to be attenuated for each channel.  
                                         TABLE 1                           Demux Control System Line Attenuator Control Truth Table            2D/3D   FSWAP   Vs   Hs   CTRL A   CTRL B               0   X   X   X   0   0       1   0   1   X   1   0       1   0   0   ↑   {overscore (CTRLA)}   {overscore (CTRLB)}       1   1   1   X   0   1       1   1   0   ↑   {overscore (CTRLA)}   {overscore (CTRLB)}                  
 
         [0023]    Table 2 illustrates the Truth Table for the green swap control output. When 2D/3D is 0 (the device is in 2D mode), the green swap function is disabled by setting the CTRL GS signal to zero. In 3D mode (2D/3D is 1), the CTRL GS output follows the state of the GSWAP input. However, when a change occurs on the GSWAP input, the CTRL GS output state is switched at the following Vs to prevent image artifacts associated with swapping the green data signals between channels.  
                             TABLE 2                           Demux Control System Green Swap Control Truth Table            2D/3D   GSWAP   CTRL GS               0   0   0       1   0    0*       1   1    1*                          
 
         [0024]    [0024]FIG. 4 illustrates the block diagram of the Green Swap System. As shown in Table 3 when the CTRL GS signal is 0 the green data signals are not swapped between channels. However when the CTRL GS signal is 1 green data signals are swapped. In the preferred embodiment the Green Swap System is implemented using an RGB switch integrated circuit that has proper termination and amplification built in to the design. Other methods for swapping the green data signal between stereoscopic image data channels are also possible. Table 3 illustrates the truth table for the Green Swap system as previously discussed.  
                             TABLE 3                           Demux Control System Green Swap Control Truth Table            2D/3D   GSWAP   CTRL GS               0   0   0       1   0    0*       1   1    1*                          
 
         [0025]    The present invention has been shown and described in what are to be considered the most practical and preferred embodiments. It is anticipated that departures may be made there from and that persons skilled in the art will implement obvious modifications.