Setting Up the Warp System File: Warp Theater Set-up.doc 25 MAY 04

Setting Up the Warp System File: Warp Theater Set-up.doc 25 MAY 04 Initial Assumptions: Theater geometry has been calculated and the screens have been marked with fiducial points that represent the limits of the final image. Refer to the tutorial Marking the Wall, for overall, theater/visuals design explanations. You are using stand-alone VMS-100 1RU ScreenShaper units. By necessity you will be communicating with each one over RS-232 serial communications links. If you need to control more than two units, we recommend the purchase of a multiple channel RS-232 card for installation in the Host computer. The ScreenShaper GUI now has the ability to allow the user to switch between up to 10 COM ports. Definitions: Host computer This is the computer graphics source. It can be a single channel source or the host for a multi-headed graphics card. This is the personal computer that the ScreenShaper Graphical User Interface (GUI) will run on. Fiducial Marks A series of marks applied to the theater screen to enable the click-and-drag method of developing warp maps. Horizontal and Vertical Anchor Lines These are the grid lines that when the intersections are dragged to the fiducial marks will determine the final warped image shape. A 3:4 aspect-ratio image (1024x768) will use four lines that run horizontally (horizontal anchors) and five lines that run vertically (vertical anchors.) This will divide the image up into four pieces horizontally and three pieces vertically. Single Channel Setup Procedure: 1. Set up the projector to overscan the area into which the image will be warped. 2. Provide computer graphics input to the ScreenShaper system. While the ScreenShaper processor will output test patterns without an input, it is best to capture the input timing from the image source. 3. On the Output Setup page, set the output format of the ScreenShaper to the native resolution of the projector. 4. In the ScreenShaper GUI, Output Setup page, turn on the Output Raster Box. The image will be distorted but that is okay. Adjust the projector size and position controls to capture the entire raster box, first and last columns of pixels and the top and bottom lines. This will guarantee that the projectors will display the entire incoming image. 5. Turn off the Output Raster Box. On the Output Setup page, turn on the one-on-one-off pixel test pattern. For analog inputs, adjust the projector s pixel clock phase control to eliminate phase noise from the image. This step is important to do before warping is finally enabled. Digital (DVI-D) inputs do not require phase compensation. 6. On the Input Setup page, turn on the Input Graphics Border. This is a yellow one-pixel-wide raster box that originates from the computer graphics source. Adjust the Hstart and Vstart controls so that

the ScreenShaper will capture the entire raster box, first and last columns of pixels and the top and bottom lines. This will guarantee that the ScreenShaper will display the entire incoming image. On the Output Setup page, turn on the Output Raster Box. The Output Raster Box should exactly overlay the Input Graphics Border. 7. Turn off the Input Graphics Border. On the Warp Map Setup page, set the number of horizontal and vertical anchor lines according to the theater geometry plan. 8. Press the Edit Grid button. You will now see the set of grid lines at will cover the entire illuminated projector image. When you place the mouse pointer on any given grid intersection and click the left mouse button, it will turn red. This means you have hooked the grid point. Click and drag each grid intersection to its proper fiducial mark. Do this fast and don t pay attention to absolute accuracy at this time. When you have gotten the basic shape, press Shift-Up Arrow. This will turn the upper left grid point red indicating that you have hooked it. Up-Arrow, Down-Arrow, Right-Arrow and Left-Arrow will move the grid point in one pixel increments. This function will allow you to finetune the grid point positioning on its fiducial mark. Shift Right-Arrow, Shift Down-Arrow, etc. will let you navigate to each grid point where you will fine tune its position with Right-Arrow, Down- Arrow, etc. Do not be concerned that the grid lines sag between grid intersection points. The mathematics will only use the grid intersections for its calculations and the lines will end up being straight after the warp map has been calculated. 9. Hit Escape to exit the fine-tuning mode. Hit F1 to exit the grid editing mode. You will be prompted to give this initial grid a name. The extension type *.grd will be added automatically. This.grd file will contain your initial work and you may need to refer to it during the final phases of alignment, so make it an individual name such as screen_1_initial.grd. Once you have given the file a unique name, you can call it up at a later time by using Recall Existing Grid. If you have been working with a grid smaller than a 5x5, this pattern will have to be interpolated to a 5x5 or greater pattern in order for the Generate Warp Map mathematics to work. When you enter the number of horizontal and vertical interpolation grid lines, you will be prompted for a new file name. Make this file name different from the original working grid: screen_1_int.grd. for interpolated grid. 10. This grid file is in memory now and when you press the Generate Warp Map button, this is the grid that will be used. The software will perform the calculation and advise you that the warp map has been generated correctly. If the warp map generation has failed, press the Edit Grid button and inspect the grid map. If there are any grid line fold-overs the map will not be created. If you have performed the grid point mapping with great accuracy, this fold-over should never happen. However, if it does, please call us here at the factory and we will help with figuring out what caused the fault. 11. Press the Load button and the map will be loaded into the warp engine. Turn the warp on and the image will be compressed into the fiducial mark outline. 12. Check your work: If you had originally started with a 4x5 grid, change one of the anchor line numbers to some other value, hit Enter to change it, then change it back and hit Enter. This action forces the software to reset the grid to its original extent, in other words, you are starting over with a grid that stretches from all four corners of the input image. But, you now have warping turned on, and so the new grid will fill the fiducial-mark pattern. The grid will now be exactly registered on the fiducial marks.

13. Exit the "Edit Grid" function by pressing the F1 button. The input image should also fill the fiducial mark outline, be rectilinear and have the correct aspect ratio. 14. Save your work: Hit the Save button on the lower-left side of the GUI screen. This action will save all set-up parameters in non-volatile memory. If the device is turned off now and powered-up at a later time, these system settings will be restored exactly as they were saved. This completes the setup procedure for one channel of warp. This procedure is applicable to singleprojector displays such as sharply-curved, half-cylinder "kiosks," half-spheres, gently-curved screens, flat screens with a projector that is off-axis in two directions or rolled, both front-projected and rear-projected. Multiple Channel Warp and Edge-Blend Setup Procedure You will be following the same procedure for multiple channels of warp as you do for a single channel, except that you will be matching blend-areas on adjacent channels and edge-feathering the overlap areas. Overlap Regions When designing a theater you will have to decide how many pixels of overlap you need. Generally, the more, the better, since if you allow very few pixels of overlap the steps in the gamma curve get steep. This can be an obvious artifact. Generally speaking, a 32 pixel overlap or greater will have the best chance of being non-discernible. More often than not, the required horizontal and vertical fields-of-view (FOV) of the entire array of projectors will drive the width of the overlap regions. For example, referring to the applications note "Marking A Wall," the customer had a 90 degree required horizontal field-ofview illuminated by two 1024x768 projectors spanning 12 feet and required that the vertical FOV fill 5 feet. The integrator therefore had a full 256 pixel overlap to exploit. Now, 256 x 4 = 1024 and 256 x 3 = 768, just the aspect ratio of the projectors. So the wall was marked off into squares, each 256 pixels on a side, 7 squares horizontally and 3 squares vertically. By the same token, SXGA projectors have a 5:4 aspect ratio and the squares would again be 256 pixels on a side. The wall would be divided into 9 squares horizontally and 4 vertically. Assumptions: I will assume that the two images have "common data," that is, that the images have been "data doubled" so that you will have something to overlap and blend with. During the warping process turn off the "datadoubling, since you will need to use every pixel of both channels to accomplish the warping. First I will explain the overall procedure for warping a 256 pixel overlap and then discuss refinements such as fine-grain convergence within the overlap region as well as smaller overlap areas and nonstandard blend regions. 1. As before, illuminate the left-hand 4x3 group of squares with the first projector and the right-hand group of squares with the second projector. Again, slightly overscan the 4x3 blocks to maximize available pixels. 2. Perform the projector calibration and capture the entire image from the graphics card channels. The graphics card must be set to "Clone" mode for this step, since the GUI has to be run on each channel. The GUI will then appear in both projector's FOV.

3. Turn off the second projector's video by selecting Test Pattern: Black on the Output Setup page. Now you can work on warping projector one's image. 4. Complete the warp as noted above. Turn the Test Pattern to OFF on the second channel and restore the ScreenShaper GUI on the second projector's image. 5. On the first channel bring up the 4x3 rectilinear grid that overlays the fiducial marks exactly. This time, exit the grid using the F2 key. This restores the GUI on channel 2 but leaves the grid pattern "frozen" on the first channel. 6. Proceed with the warping process on channel 2 and use the grid points that surround the overlap region on channel 1 as the fiducial marks. It may be that you were not able to place the grid points exactly on top of the fiducial marks when working with channel 1. Now is the chance to exactly register channel 2's grid points with channel 1's. Excellent convergence in the overlap region is what you need at this point. 7. Complete the warp process on channel 2 and put up the rectilinear grid. The entire screen will be filled with the grids, the "frozen" grid on the left-hand, channel 1 projector and the new grid on the right-hand, channel 2 projector. The overlap area will be double-lit. 8. Check your work. It may be that you need to tweak the grid point locations on channel 2 to improve convergence. Exit the Edit Grid function using the F1 key, turn off warping, put up the "screen_2_int" grid and make your corrections. I will move a given grid point side to side and up and down and watch for the best overlay of the lines. You can tell when convergence is getting bad by looking for separating lines and fuzzy grid points. Convergence is getting good when the lines look blacker. 9. Re-calculate the warp, load it, put up the rectilinear grid pattern and admire your work. 10. Exit the Edit Grid function on channel 2. Switch to channel 1 on the now-visible GUI, pull up the Output Setup page and turn Image Freeze off. You will now have two warped images showing the GUI in each FOV. 11. Turn the graphics card display scheme from "Clone" to "Horizontal Span." Turn on data doubling and you are ready to edge-blend. Additional Overlap Convergence Procedure There will be situations when additional convergence of overlap areas will be required. I will use the 256 pixel overlap region for the example. As you have noted, the overlap region is a strip 256 pixels wide and 3 squares tall. This technique will divide the strip into 4 vertical stripes 64 pixels in width. 1. Proceed as before to develop the grid for a 4:3 aspect ratio screen that is 7 squares across and 3 tall. 2. When it is time to develop the interpolated grid, use 4 horizontal anchors and 17 vertical anchors. This divides the screen into 16 64-pixel wide slices. Ignore the grid points outside of the overlap area. 3. Leave the left-hand set of grid lines alone, hit F2 to exit the gridding function and leave the grid frozen up on the left-hand screen.

4. Perform the same interpolation for the right-hand screen. On the right-hand screen, carefully align the overlap region to the left-hand overlap grid points. As you can see this technique results in the development of extra "virtual grid points" that are not required during the original screen marking procedure. The rest of the image outside of the overlap region does not need convergence with itself, of course, and so you can ignore those points. I arbitrarily decided on dividing the overlap region into 4 vertical stripes. You could just as well have used 2 or 3. Choose one, divide the screen up into equal pieces, get that number, add one and enter that as the numbers of vertical anchors. Non-Standard Overlap Widths There are some scenarios in theater design that require narrow overlap areas. In one installed theater, the customer required 7 projector channels arranged to illuminate 270 of cylindrical screen. The trigonometry resulted in each projector having a total horizontal field of view of 39 and a vertical field of view of 31. The desired overlap region was 2. The projectors used were 1280x1024 and had an aspect ratio of 5:4. Proportionally, 2 degrees equaled 65.64 pixels and the overlap region was adjusted to equal 66 pixels. An additional function was built into the Graphical User Interface to handle this requirement. It is known as "unevenly-spaced grid." When the "evenly-spaced grid" is unclicked on the Warp Setup page, this function is activated. This function allows the user to set the positions of the horizontal and vertical anchor lines by pixel position. The values entered in to the anchor position table on the Warp Setup page were: horizontal anchor position: 0, 65, 639, 1213, 1280; vertical anchor position: 0, 66, 511, 958, 1024. This results in a grid that is designed to fit the fiducial mark array pictured below. 2 39 35 31 27 2 HORIZON LINE AT ZERO DEGREES ELEVATION Standard But Narrow Overlap Regions There is another consideration to designing the screen and fiducial mark positions. This can make the

projectionist's job considerably easier and allow a high degree of convergence between adjacent projectors in the overlap region. There is a benefit to dividing the screen into regular size blocks and picking the size of the block to match the width of the overlap region. In the previous example, the requirement was for the overlap area to be 66 pixels wide. I simply had to work with that. I would have preferred to have used 64 pixels. Here is the method and it will be obvious why this is a valuable technique. Suppose that the overlap region will be 160 pixels wide, out of a horizontal 1280 pixels. This means that there can be 8 blocks 160 pixels wide across the SXGA image and 8 blocks 96 pixels vertically. Mark the screen as shown in the following diagram: 1280 160 160 96 1024 17 17 At this point, create an interpolated grid of 17x17. This will generate "virtual" grid points throughout the image, but most importantly throughout the overlap areas, allowing fine-grain positioning of adjacent grid point sets. The whole point of this exercise was to cut the number of required fiducial marks to a minimum, reducing the projectionist's work-load in marking the screen. The five by three array is the smallest number of elements required to accurately define the warp. Interpolation takes care of the points for overlap registration.