Presentation on theme: "Electronic Projection Mapping using Warp & Blend"— Presentation transcript:
1 Electronic Projection Mapping using Warp & Blend Introduction by:Tim Brooksbank, CEO, Calibre UK Ltd.Technical Presentation by:Paul Carey, President, MSI Inc.
2 Background Modern projectors used fixed pixel numbers and positions To shape the picture to fit a screen or to overlay an object it is necessary to modify the shape of the image content in that signalTo seamlessly blend multiple projectors to create very large or different shape images, the intensity of overlapping pixels must be accurately controlledThis presentation discusses how this can be achieved
3 The Ideal WorldProjectors should be central and perpendicular to a flat screenProjectors should be the correct distance from the screen such that the picture just fills the screenThe screen should be flatScreen aspect ratio should match projector’s native aspect ratioOne projector is bright enough with suitable optics to generate the whole imageIn real world use this is often not the case
4 The Real World The screen is not always flat Projection is used in many applicationsother than cinemas and traditional lecturetheaters: Immersive Caves and Domes,for Simulation, Themed Entertainment,Museums and Architect Designed Spacesas well as for Creative Use on Stage/Set.Screen aspect ratio and shape is often a creativedecision of the presentation or experience designer
5 Warp & Blend or Projection Mapping Warp or Projection Mapping is the manipulation of the projected signal to correct for distortions due to screen geometry and off axis projection. This is the mapping of the projector onto the surface.Blend is the term used to describe the lightness or intensity mapping of multiple projectors such that the array appears as a single projector. This is the mapping of several projectors into one image.Important note - Warping does not change the optical characteristics of the projectorDepth of field is an optical function, the image needs to remain focused, this cannot be corrected electronically
6 Why warp or map Warping by small amounts examples are overlaying one projected image on top of another for extra brightness or 3D alignmentTwo projectors cannot be in the same space so will have some errors in overlayWarping can be extremean example from a London museum is making the image overlay an object shaped to look like a stained glass window in a church
7 Why warp or map A steeply angled and off center mount warped so that the imageprojected shows thecircle correctly
8 Why warp and blendWhen using two 4:3 projectors for a 16:9 screen or two 16:9 projectors for a 2.35:1 film applicationArchitects often curve a screen to fit the buildingHere is an example in a Londonbank where the screen at the frontof the theatre continues aroundtwo curves to the side wall
9 Why warp and blendDesigners of public interactive exhibits are not restricted by conventionIn a London museum visitorswalk on the exhibit,the screen is both on a walland on the floor.There are five projectors, the threeon the wall project at extreme angles
10 Why warp and blend Another example in a museum: 3 projectors used, 2 project on wall, 1 on floorAll located high in the ceilingproducing an image that interactswith physical scenery
11 Multi-Projector Arrays Multiple projectors are indicated when:- Aspect ratio of the design differs significantly from the aspect ratio of the projector- Projector placement (short throw or position) does not cover the surface design with a single projector- Brightness is desiredThe brightness of the image on the screen is a function of the amount of light produced by the projector(s) divided across the area of your screenTiling an array of projector images is a method of getting more light on the screen, each projector covers a small area thereby increasing the overall brightnessBlending the tiled array of projectors makes the image look like one image
12 Blend and Warp - Three Options Create dedicated source material or modify content at sourceModify the source material using an external processing boxModify the source material within the projector
13 Blend and Warp – How it Works Blending relies on feathering the light from each projector in the overlapping areasThis process is achieved by controlling light intensity, this differs from video level as it must take account of projector gammaMatched projectors are important to achieve good results, including matching lamps and lamp-burn hoursContrast and color enhancing projector effects such as Vivid Color and “Brilliant Color” must be disabled as these cause gamma errors
14 Blend and Warp – Option 1 Create dedicated source material Used in permanent displaysCostly and inflexibleInappropriate where content is changed regularlyAlternate content cannot be presentedMay be harder or more expensive to re-calibrate as that process is interactive with content producerCan be advantageous with screen shapes which cannot be mapped using curve fitting or are discontinous
15 Blend and Warp – Option 2Modify the source material between source and projector using and external boxFlexibleCan be used with any projectorAny content can be shownAllows extremes of adjustment, provided the surface is continuous without hard angles – uses curve fittingWorks with any source, doesn’t require application specific video servers
16 Blend and Warp – Option 3Modify the source material within the projectorSome high end projectors now offer this optionOption stays with projectorRequires expensive projector optionsLimited projector choiceHard to transition to alternative projectorsRange of adjustment usually limitedUser interface to control warping is usually rudimentary
17 Projector Choice and Utilization Multiple projector arrays can improve projector utilization on the screen to improve image performanceIf the overall aspect ratio of the display is for example 3.5:1 then a single 16:9 projector would only utilize 1.78/3.5 of the imager. 50% of the light and pixels would be lost (not contribute to the image.)If that 3:5:1 aspect ratio display was formed with 3, 4x3 projectors then 3 x 1.33 ~ 4:1 88% of the imager is utilized (12% overlap to equal 3.5). The latter maximizes lumens per sq foot.
18 How to blend and warpFor more detail the example being used is two dedicated processors to two projectorsLet’s assumeThe projectors aremounted off angleTwo 4:3 projectors areavailableA 16:9 image is required
19 How to blend and warp 2 Align the projectors optically Maximize the number of pixels on the screen area but use the same amount of zoom on each projector if possible, this ensures the lumens per square foot per projector are equalEnsure the optical image covers the screen, warping can only operate within the projected area.Choose a suitable amount of overlap, this should be at least 10%, preferably 20% or more to get good results. In the special case of making a 16:9 image from two 4:3 projectors it is 2/3.Ensure focus is accurate before you start to warp and blend - many projection lenses change the size of the projected image as focus is adjusted
20 How to blend and warp 3 Choose the native resolution of the projector The projector has a fixed display resolutionA dedicated scaler will generally do a better job of scaling than an inbuilt scaler
21 How to blend and warp 4Choose the position of the projectors in the matrix. This defines which blend regions are appropriateIt defines the section of image to be displayed by each projector when ‘Auto Zoom’ mode is used
22 How to blend and warp 5 Choose the test alignment pattern This highlights the blend region to make it easy to seeThis is also an adjustable cursor positioned at the edge of the blend (follows ‘blend width adjustment’)
23 How to blend and warp 6 Choose the Cross Hatch test pattern The cross hatch is scaledto fit the tiled imageThe ‘F’ confirms theprojection orientationCross hatch is an easy wayto align the warpColour is alternates to aidalignment
24 How to blend and warp 7Warp the images to fit the screen or projection target object with either four corner adjustment or via the warp map application
25 How to blend and warp 8There are two methods available to achieve the warpFour Corner adjustment is very efficient for alignment on a flat screen as linearity is automatically compensated when implemented wellIndependent X and Y adjustmentof each corner, sometimescalled four corner pinning
26 How to blend and warp 9 Warp Map PC drag and drop mesh application This is very efficient for complex shapes & curved surfaces as well as for correcting lens distortionEase of use depends on quality of configuration tools
27 How to blend and warp 10Auto-calibration software systems also exist for some hardware systems:These rely on camera feedbackFast and efficient, ideal for systems which need accurate alignment or need re-calibrating regularlyA must for stacked projectors if sub-pixel precise alignment is required, e.g. 3D & 2D compatible stereoExpensive, usually priced per channel (projector)Require controlled ambient lighting conditions to achieve reliable results
28 How to blend and warp 11 Choose S-Curve blend The alignment shading disappearsThe brightness of the blended regions each follow an S shaped curve to maintain 100% signal brightness across the blended region, crossing in the middle each at 50%.The S curve is performing lightness mapping such that at any point in the overlapping region the sum of the two contributing projectors is unity (equal lumens per sq ft)
29 Display input signal Choose how to display image: ● preserve original content aspect ratio● fill the available screen,ignoring content aspect ratio● fill the screen but crop image(zoom) to preserve content aspect ratio – this is often desired
30 Additional options Black level correction of a tiled image: Where projectors are tiled and the ambient light level is well controlled black level leakage” is visibleAll projectors pass some light even when the signal is blackSome processors offer compensation for this effectBlack levels are raised in individual areas to provide a smooth overall imageRequires very high processing bit depth if greyscale banding and quantization noise are to be avoided, 48 bits/pixel typicallyReduces image contrast ratio drastically so should be avoided except where essential, e.g. in dark viewing environment.Very Important: Before correcting black level, the black balance must be confirmed on all projectors. If there is an R,G or B bias, no amount of correction can be applied that will achieve an acceptable blend or seamless image.
31 Additional options Black level correction of a tiled image Note central projector requires 9 separate correction zones!