Automatic Calibration

Overview

The automatic calibration (or auto-alignment) is recommended for multi-projectors setups to visually combine several projected images into a single seamless image. This technique is recommended for non-planar screens like domes or cylindrical panoramas. It can also be effectively used on planar and rectangular screens to speed up image warping and the blending process as well as to achieve more precise results in geometry and brightness.

In Screenbrerry both manual and automatic calibrations can be applied either separately or combined together.

Creating a Node Graph for Automatic Calibration

To create a node graph for automatic calibration:

  1. In the Node Graph, add a Canvas node.
  2. Add the Canvas Editor widget to your workspace and make sure that the Displays option is selected in the view mode dropdown menu.
  3. In the Canvas Editor, press the Create Display Array button. In the dialog box, enter the number of Rows and Columns to create a grid with a number of cells that matches the number of projectors* in your setup, select CalibratorPatch as the Patch Type, and press OK. As a result, a node tree in the Node Graph is created that consists of the Calibrator node connected to the CalibratorPatch nodes, each of which is connected to one of the Display nodes, which in turn are connected to the Canvas node.
  4. In the Node Graph, add a MediaPlayer node (or any other media source node) and connect its Image output parameter to the Source input parameter of the Calibrator node.
  5. In the Node Graph, add a Camera node, then:
    • Connect its Camera output parameter to the Camera input parameter of the Calibrator node, and
    • Connect its Image output parameter to the Camera Image input parameter of the Calibrator node.

*The number and arrangement of displays in a display array should match the settings and topology of the GPU driver settings.

Creating the Calibration Node Graph for a typical 4-projector set-up

Setting Up Projectors

The following steps should be performed to set up projectors properly:

  1. Ensure that the projectors have equal or comparable lamp life. Replace the lamps if necessary. For projectors with solid-state laser light source, select the same brightness mode.
  2. Ensure that the projectors are fixed firmly and will not move during the calibration process.
  3. Connect the projectors to the corresponding video card outputs of the Screenberry Server with the help of video signal cables.
  4. Turn on all projectors.
  5. Using the projector’s menu, turn on Test Patterns to confirm that the projected images cover the whole surface of a target projection area (screen) and overlap sufficiently. The recommended overlap region is 5 to 15% on each side of the adjacent images. Adjust the zoom, lens shift, focus, and position of the projectors, if necessary.*

Example of the correct projections overlapping in a 4-projector dome setup

  1. Ensure that all additional correction settings on the projectors are turned off (like Auto Keystone Correction, Keystone and Geometry Corrections, unnecessary Color Corrections), and no additional functionality (like Picture-in-Picture mode, etc.) is being used. Confirm that the projector’s dynamic contrast and auto-brightness features (Auto Iris, Dynamic, Smart Eco, etc.) are turned off.
  2. Verify that all projectors are switched to the same Color Mode (sRGB, Presentation, Cinema, etc.).**
  3. To ensure that the signal is passing correctly and that the projectors are connected to the correct video card ports, use the Test Pattern option of the Calibration Wizard:
    1. Add the Calibration Wizard widget by selecting Window > Calibration Wizard from the main menu.
    2. Open the Show Test Pattern drop-down list.
    3. Select the White (No Blends) test pattern to check that the projectors are displaying images within the intended area and are overlapping correctly.
    4. Select the Focus Grid test pattern to check that all projectors are in focus.
    5. Use other test patterns available in the Show Test Pattern drop-down list to check the contrast, brightness, color and sharpness settings of the projectors.

*Refer to your projector manufacturer’s user guide for details.
**The names of the color modes can vary depending on the projector model and manufacturer.

Setting Up the Calibration Camera

Equipment required for the single camera automatic calibration:

  • DSLR Camera (see the list of the supported cameras),
  • Tripod with a Ball Head,
  • USB Cable of a sufficient length for connecting the Camera to the Screenberry Server,
  • Data Interface USB Cable compatible with the camera,
  • Memory Card compatible with the camera.

List of Supported Cameras for Windows

 NikonD33, D3s, D3x, D300, D300S, D3500, D3400, D3300, D3200, D3100, D3000, D4, D40, D5, D500, D5600, D5500, D5300, D5200, D5100, D5000, D60, D600, D610, D700, D750, D7500, D7200, D7100, D7000, D80, D810, D810A, D800, D800E, D850, D90, Df, Z50, Z6, Z7
 CanonEOS-1D Mark III, EOS-1D Mark IV, EOS-1D X Mark II, EOS 100D, EOS 1000D, EOS 1100D, EOS 1200D, EOS 1300D, EOS 200D, EOS 2000D, EOS 40D, EOS 450D, EOS 4000D, EOS 5D Mark II, EOS 5D Mark III, EOS 5D Mark IV, EOS 50D, EOS 500D, EOS 550D, EOS 6D, EOS 6D Mark II, EOS 60D, EOS 600D, EOS 7D, EOS 70D, EOS 77D, EOS 700D, EOS 760D, EOS 80D, EOS 800D, EOS 90D, EOS M, EOS M50, EOS M5, EOS M6, EOS M6 Mark II, EOS M100, EOS M200, Rebel T3, Rebel T5, Rebel T6, EOS R, EOS RP, PowerShot SX70 HS, PowerShot G5 X Mark II, PowerShot G7 X Mark III
 Sonyα7, α7 II, α7R, α7R II, α7S, α5000, α5100, αv6000, α6300, α6500, NEX-5R, NEX-5T, NEX-6, HX60, HX80, HX90, HX400, WX500, RX10 II, RX100 III, RX100 IV, RX100 V, FDR-X3000R, FDR-X1000V, HDR-AS50, HDR-AS300R, DSC-QX30, DSC-QX100

The camera models highlighted in bold are the ones that have been tested and recommended for automatic calibration.

List of Supported Cameras for Linux

http://www.gphoto.org/proj/libgphoto2/support.php

Selecting a Camera Lens

It is recommended to use a lens with a focal length suitable for the projection screen topology:

  1. Normal or Wide-angle lenses are used for planar projection surfaces which are usually rectangular.
  2. Normal or Wide-angle lenses are used for non-planar projection surfaces such as a curved rectangular display.
  3. Circular Fisheye lenses are used for non-planar projection surfaces such as a dome or cylindrical panorama.

Camera Settings

It is important that camera post-processing parameters are switched off.

Example of correct Nikon camera* settings:

Set Picture ControlSD (Standard). All parameters should be set to zero, including sharpening.
Active D-LightningOFF 
High ISO NROFF 
Auto Distortion ControlOFF 
Long Exposure NROFF 
Automatic focusOFF 
Auto Sensitivity ControlOFF (Nikon 3400 only)
White BalanceCloudy

*For Nikon D5000/D5100/D5200.

If the camera prompts you to enter the date and time after being turned on, press the OK button.

Set the camera mode dial to Manual (M).

Switch the lens focus to Manual (M) and focus the lens manually using the Focus Grid test pattern of the Calibration Wizard as a reference.

Positioning the Camera

Camera positioning for Dome Projection

Camera position guidelines:

  • Mount the camera steadily on a tripod and position it in a way that it captures the entire projection area (screen).
  • Position the camera tripod on the floor surface below the dome so the camera lens is aligned with the dome’s zenith.
  • Ensure that the camera tilt matches the dome tilt.

Camera position. Side view.

Camera position. Zenith view.

  • Position the camera lens directly below the projectors’ lenses so that the camera does not cast shadows on the dome screen.
  • Orient the camera so that the bottom of the picture frame corresponds to the front of the dome and the top of the frame corresponds to the rear end of the dome.

Calibration camera position in the dome. Top view.

Note:
The camera tripod should be installed on a firm and stable horizontal surface to avoid movements and vibrations during the calibration process.

After positioning the camera:

 

  1. Remove the lens cap and anti-glare ring.
  1. Connect the camera to the Screenberry Server using a USB cable.
  2. Ensure that the camera memory card has sufficient free space for at least one photo in the RAW format.
  3. Ensure that the camera battery is sufficiently charged. In the case of using a power adapter, connect the camera to a power outlet.
  4. Ensure that there are no obstructing objects between the screen and the camera that could interfere with the calibration process.
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Warning:
The entire projected image should be within the camera view, and there should be no shadows on the screen.

Multiple camera calibration

Screenberry also supports multiple cameras’ automatic calibration. 

Automatic Calibration Presets

The Calibrator Wizard widget (Window > Calibrator Wizard) offers three calibration presets:

  • Geometry calibration provides geometry alignment and edge blending. It normally takes about 30 seconds per projector and includes the Masks, Geometry, and Blends calibration stages.
  • Geometry + Intensity calibration provides geometry alignment, edge blending, and black and white level compensation. It normally takes about 1.5 minutes per projector and includes the Masks, Geometry, Blends, and Intensity calibration stages.
  • Geometry + Intensity + Gamma calibration has all the Standard calibration features with the addition of gamma correction to ensure image color uniformity within blends. It usually takes about 15-30 minutes and includes the Masks, Geometry, Blends, Colors, and Intensity calibration stages.

Note:
The initial Standard and Standard with Colors Stage calibration may take longer as more pictures at a slow shutter speed should be taken for automatic adjustment of the camera for black calibration.

Note:
The Standard with Colors Stage mode is required only if you are using DLP single-chip projectors with Brilliant Color enabled. This calibration is required for the initial setup, or in any of the following cases:

  • After the projector lamps have been replaced following extensive use.
  • When visible color shifts in the blends between projections become apparent.
  • After the projector color mode (Presentation (Game, PC), Cinema, sRGB, etc.) had been changed.

Note:
Once the Colors calibration stage is completed, the gamma correction maps are stored in the LUT tables and applied every time that the Geometry and Geometry + Intensity calibrations are run.

Checking Projectors and Camera Positioning

When the calibration mode is selected, the system automatically takes a test photo.

If the camera is not connected or not functioning properly, an Error message will appear.

Based on the test photo, adjustments can be made, if necessary, to:

  • Camera rotation and tilt.
  • The positioning of projectors and projected images overlapping.
  • The positioning and focus of the camera.

After adjustments are made, press the Capture button to take another test photo. Make further adjustments if necessary. Repeat these steps until the camera and projection layout are set up as required.

Defining the Calibration Projection Area

The objects outside the projection area (light sources, trusses, etc) can reflect or emit light and, thus affecting the calibration results distorting calibration geometry or influencing black level compensation and brightness balance. Therefore, it is important to precisely define the projection area — anything inside the specified area is calibrated while everything outside is ignored.

Open the Calibration Area dropdown menu to select one of three screen area setting modes:

  • Automatic. Using the calibration patterns, the Calibration Wizard identifies the borders of the projection area automatically.
  • Manual (recommended). In this mode, a user can manually define a more precise bounding shape for the projection area. This approach significantly improves calibration quality by excluding undesired areas that should not be covered by the projection.
    To adjust the mask, do the following:

    • In Bounding Box mode, scale the mask by dragging the handles.
    • In Circular mode, apply fine adjustments to the mask by dragging the handles on the curve. You can switch to this mode by selecting the Bounding Box Off checkbox.

Bounding Box mode

Circular mode

For more adjustment precision, zoom and pan the view by using the mouse scroll wheel (scrolling it to zoom, and holding it to pan) or by clicking the Zoom and Pan buttons in the top right corner and moving the mouse.

To reset the mask to its default state, press the Reset button .

Note:
The mask settings defined by the user are saved automatically, and loaded during the next calibration session.

  • Full Camera Frame. In this mode, the Calibration Wizard automatically recognizes the entire photo frame as a projection area and positions the content to fit within the borders of the test photo.

Running Calibration

Once the calibration projection area is defined, press the Start (Selected Calibration Preset) button to start the calibration. During calibration, the Calibrator Wizard displays the calibration progress bar, the current calibration stage, and photos of the calibration patterns projected on the screen.

The calibration process can be interrupted by pressing the Abort button . The Abort button stays active during calibration and deactivates once the calibration process is finished successfully.

Press the Finish button  when the calibration process is completed. The Finish button is inactive during the calibration process and activates when calibration is completed.

Important:

To achieve the best calibration results, during the calibration process:

  • No object or person should obstruct the projectors’ light beams. If during the calibration the presence of personnel is required, they must remain below the projection line and out of camera view range.
  • No light sources should be present in the dome. Lamps, monitors, phone screens, etc. should be turned off or, at the very least, set to minimum brightness.

Stages of Automatic Calibration

  1. During the Masks stage, a series of black and white line patterns is generated to define a projection area for each projector.

Black and white line pattern

Resulting mask

2. During the Geometry stage, a series of blob patterns is projected to generate the displacement maps for each projector.

Geometry pattern blobs

Generated geometry displacement map

3. The Blends stage is used to generate brightness gradients for each projector to enable a smooth and even transition for the overlapping areas between projections.

Projector #1 blend map

Projector #2 blend map

4. The Colors (Gamma Correction) stage is used to compensate for visible color / brightness shifts caused by non-linear gamma distortions that can occur when color modes with “boosted gamma” (like Brilliant Color) are set on DLP single-chip projectors. A series of color patterns are projected, and as a result, a Look Up Table (LUT) for a specific projector model is generated.

Example of color patterns used for Gamma Correction

Note:
The Gamma Correction calibration stage is required for the initial setup, after projector lamp replacements, or following extensive use, when visible color/brightness shifts in the blends between projections become apparent, which can be checked by using the Red, Green, Blue test patterns.

5. The Intensity stage is used to adjust the brightness in low (dark) and high (bright) intensity ranges to equalize the brightness levels between projections.

Before Black Level Compensation

After Black Level Compensation

Before Brightness Balance

After Brightness Balance

Post-Calibration Dome Image Adjustment

After the completion of automatic calibration, further adjustments to compensate for the position, orientation, and lens distortion of the calibration camera can be made using the DomeTransform node. For more information, see DomeTransform.

Reviewing Calibration Images (for Advanced Users)

If the calibration results are not satisfactory, or if a failure occurred during calibration resulting in an error message, the calibration images can be reviewed to identify the problem.

To review the calibration data, press the Open Calibration Images Viewer button  in the Calibrator Wizard widget and choose the image file for the required calibration stage from the Select Image drop-down list.

Exporting Calibration Files

Calibration files may be exported with the help of the DomeSDKSaver node, which saves the calibration files of the combined projection image in the proprietary .sbraw and .png file formats. These files can be used in the Front Pictures SDK plugins developed for the Unreal® Engine 4, Unity®, and TouchDesigner applications. The .sbraw file format contains floating-point pixel values.

Note:
Export of calibration files is disabled in the demo version of Screenberry.