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 tab, add a Canvas node.
  2. In the Display Editor tab, 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 fields that match 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 is connected to the Canvas node.
  3. In the Node Graph tab, 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 (see Creating Links Between Nodes Manually).
  4. In the Node Graph tab, 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 typical 4-projector set-up

Setting Up Projectors

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

  1. Make sure 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. Make sure 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. Make sure 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. Be sure to turn off the projector dynamic contrast / auto-brightness features (Auto Iris / Dynamiс / Smart Eco, etc.).
  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. Select Media Player tab > Window > Calibration Wizard.
    2. Open the Show Test Pattern drop-down list.
    3. Select White (No Blends) to check that the projectors are displaying images within the intended area and are overlapping correctly.
    4. Select Focus Grid test pattern to check that all projectors are in focus.
    5. Use other test patterns available in the 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

Highlighted in bold are the camera models that are 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’s recommended to use a lens with a focal length appropriate 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’s 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:

  • The camera should be mounted steadily on a tripod and positioned in a way that the camera can capture the full 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.
  • The camera tilt should correspond to the tilt of the dome.

Camera position. Side view.

Camera position. Zenith view.

  • The camera lens should be positioned right below the projectors’ lenses and the camera should not cast shadows on the dome screen.
  • Orient the camera so 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 via USB cable.
  2. Make sure that the camera memory card has sufficient free space for at least one photo in the RAW format.
  3. Make sure that the camera battery is sufficiently charged. In the case of using a power adapter, connect the camera to a power outlet.
  4. Make sure there are no obstructing objects between the screen and the camera that could interfere with the calibration process.
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Warning:
The whole projected image should be within the camera view, and there should be no shadows on the screen.

Multiple camera calibration

Screenberry also supports multiple camera automatic calibration. See Link for more details.

Automatic Calibration Modes

The Calibrator Wizard (Media Player tab > Window > Calibrator Wizard) offers three calibration modes:

  • Geometry (Fast) calibration provides geometry alignment and edge blending. It normally takes about 30 seconds per projector and includes Masks, Geometry, and Blends calibration stages.
  • Geometry + Intensity (Standard) calibration provides geometry alignment, edge blending, and black and white level compensation. It normally takes about 1.5 minutes per projector and includes Masks, Geometry, Blends, and Intensity calibration stages.
  • Geometry + Intensity + Gamma (Standard with Colors Stage) 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 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, after projector lamps replacements, following extensive use, when visible color shifts in the blends between projections become apparent, or after the projector color mode (Presentation (Game, PC), Cinema, sRGB) is changed.

Note:
Once Colors Stage is calibrated, the Gamma Correction maps are stored in LUT tables and applied each time when Fast and Standard calibrations are run.

Checking Projectors and Camera Positioning

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

If the camera is not connected or not working properly, an Error message will appear. (See Troubleshooting )

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

  • 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 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 affect the calibration results distorting calibration geometry or influencing black level compensation and brightness balance. That’s why it is important to define the exact projection area everything inside the specified area will be calibrated, while everything outside it will be ignored.

Open the Calibration Area drop-down 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 define the projection area by creating a more precise bounding shape manually. This approach substantially improves calibration quality by excluding unwanted areas which should not be covered by the projection. To adjust the mask, you can scale it by dragging the handles in Bounding Box mode or switch to Circular mode by checking the Bounding Box Off checkbox and dragging the handles on the curve for fine adjustments.

Bounding Box mode

Circular mode

The edges of the mask should be aligned exactly with the borders of the projection area. For more precision, zoom in and out or pan the view using the mouse scroll wheel or by clicking the Zoom and Pan buttons in the top right corner. 

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 whole 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 (Chosen Calibration Mode) button to start the calibration. The Calibrator Wizard displays the calibration progress bar, the current calibration stage, and photos of 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:

For achieving the best results during the calibration:

  • No object/person should obstruct the projectors’ light beams. If during the calibration the presence of personnel is required, they must position themselves below the projection line and out of camera view range.
  • No light sources should be present in the dome. Lamps, monitors and 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 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

Reviewing Calibration Images (for Advanced Users)

If the calibration results are not satisfactory or the calibration process was interrupted with an error message, the calibration images could be reviewed to identify the problem.

To review the Calibration data, press the Open Calibration Images Viewer button in the Calibrator Wizard and open the Select image dropdown list to choose the image file for the required calibration stage.

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 pixel data in floating-point numbers.

See more information on Front Pictures SDK.

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