Calibration Guide

Calibration Guide

About Pixellot

Pixellot offers automated sports production solutions that provide affordable alternatives to traditional video capture, production, and distribution systems for professional and semi-professional sports events. Founded in 2013, Pixellot’s AI technology solution streamlines production workflow by deploying an unmanned multicamera system in a fixed location, with additional angles as required, to cover the entire field, offering a stitched panoramic image. Advanced algorithms enable automatic coverage of the flow of play and generate highlights. Pixellot systems are deployed by broadcasters, production companies, clubs, federations, universities, high schools, sports portals, and coaching solution providers around the globe.

For more information visit: www.pixellot.tv


Legal Notice

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The material furnished in this document is believed to be accurate and reliable. However, no responsibility is assumed by Pixellot Ltd. for the use of this document or any material included herein. Pixellot Ltd. reserves the right to make changes to this document or any material included herein at any time and without notice. 

For more information visit: www.pixellot.tv 

Copyright © 2022 Pixellot Ltd.

All Rights Reserved.


1.0 Introduction

As part of the initial setup and configuration of the system, it is necessary to configure the calibration and color balance for the system. This procedure should be performed by a trained Pixellot support engineer. The purpose of this procedure is to assist the Pixellot algorithms in stitching the input from the two cameras into one seamlessly integrated image and to configure the desired color balance. The calibration procedure also defines the areas of the image that are relevant to the game action, enabling the Pixellot Automatic Production AI algorithms to focus on the essential activity.

There are two elements of this procedure: 

  1. Calibration - aligns the two images so that there is no visible 'seem' where the two images meet. It also defines the Field Region which enables Pixellot Automated Production to identify relevant game.

  2. Color Balance – compensates for discrepancies in the coloring of the images from the two cameras. It also enables adjustment of the overall color settings.


1.1  About the Pixellot S2 System

The Pixellot S2 system is comprised of a specially designed CHU (Camera Head Unit) that captures a panoramic image of the entire playing field and a VPU (Video Processing Unit) which processes the image feed and prepares it for distribution.

  1. CHU - The CHU consists of two wide angle cameras which combine to provide up to 180° video coverage capturing a panoramic view of the entire playing field. It also contains two mics which capture the stadium sounds.

  1. VPU - The VPU receives the feeds from the two cameras via Ethernet cables and stitches the feeds into a unified video capture of the entire playing field. The VPU applies Pixellot's patented Automatic Production AI algorithms to produce a professional quality broadcast of the sports event for cloud-based distribution to mobile devices and web platforms.


2.0  Calibration Prerequisites

The calibration procedure can only be done after the installation has been completed. For an explanation of the installation process, see the relevant Pixellot Installation Guide. Before beginning the Calibration procedure make sure that the following elements are in place:

  1. The CHU is properly installed
  2. The VPU is installed and powered on
  3. The camera has been paired and the CHU settings have been finalized
In addition, the following prerequisites must be in place in order to do the Calibration procedure.
  1. The entire court/field is lit up by daylight or full stadium lighting (with no areas covered in shadow)
  2. The sidelines and corners are clearly marked (for a soccer field, it is preferable for the corner flags to be in place)
  3. The VPU is accessible with a monitor, keyboard and mouse attached


3.0  Logging into the Engineering Station

The calibration and color balance procedures must be performed at the venue, accessing the VPU directly by connecting a monitor, keyboard and mouse. The operation is performed using Pixellot's Engineering Station application.

To login to the Engineering Station:
  1. In the Pixellot Applications folder on the Desktop, click VPU Management.
    The VPU Management UI opens. 
  2. Select the Configuration tab
  3. In the Configuration tab, click Enter Setup Mode. The VPU is activated and the Engineering Station application opens, showing the Configuration tab.
It takes a few minutes for the system to initialize. Once the initialization has been completed the Engineering Station will become active. You may need to minimize some windows showing technical data to make the Engineering Station window visible.


4.0   Step 1 - Calibration

The Calibration 'teaches' the VPU how to process the video feed from the two cameras in order to create a unified image of the entire playing field.

There are two parts of the Calibration procedure.
  1. Stitching the Image – this procedure aligns the two images so that there is no visible 'seam' where the two images meet.
  2. Frame Calibration – this procedure defines the Field Region which is monitored by Pixellot Automatic Production for identifying game action. It also sets a Panoramic Image Frame that designates how the full panoramic image is shown.

4.1   Calibrating UI Elements



The Calibration screen contains the following UI Elements:

  1. Navigation Tab – the main navigation for selecting various tabs in the Engineering Station UI.

  2. Top Command Bar – includes command buttons for selecting the sport type and controlling the overall progress of the calibration procedure (e.g. Approve, Undo and Reset).

  3. Main Image Window – shows the full panoramic image of the field, combining input from both cameras. Clicking on the image shows a zoom-in view of the selected area, which is used for marking key points throughout the configuration procedure.

  4. Calibration Controls – contains the input fields and buttons that are used for the various stages of the calibration procedure.

  5. Panorama Adjustment Controls – contains the buttons used for adjusting the panoramic frame shown in the Main Image window.

  6. Calibration Details Pane – view and edit details of the field dimensions and view details about the various points marked for calibration.

  7. Field Region Schematic Diagram – a schematic diagram of the field dimensions with indicators for marking the various field points.


4.2   Calibrating the System (multi camera)

The following procedures describe the basic work flow for performing the initial calibration for the Pixellot S2 system.

For the sake of clarity, the procedures are described in a specific order moving from top to bottom, left to right and Camera 2 to Camera 1. This is for the sake of clarity only and is not a required order of activity. 
  1. In the Engineering Station application, select the Calibration tab.
    The Calibration screen is displayed, showing snapshot images from each of the two cameras, separated by a red line down the middle.
  2. Click Sport Type in the top command bar.
    The Sport Types window is displayed.

  3. Click Add next to the sport type for which the system is being configured.

  4. Click Close.


4.3   Stitching Images (multi camera)

Stitching is performed by creating a frame of reference by which the system can identify places where the two images overlap and align the images accordingly. This is done using an iterative approach by which each calibration increases the precision of the integration. The initial calibration is done by identifying sets of Tie Points, i.e. points in the two images that represent an identical location. Then, the calibration is refined by identifying points that run along straight lines in both the vertical and horizontal directions.

Marking Tie Points involves identifying landmarks that appear in the images from both cameras (i.e. the overlapping area). Carefully mark several pairs of points in the images from both of the cameras. Use the following guidelines for selecting Tie Points:

  1. Use clearly identifiable landmarks to ensure that the points are in the identical location.
  2. Mark a specific corner or edge of the landmark.
  3. Make sure that points are marked at more or less regular intervals from the top of the image to the bottom.
To set the initial tie points:
  1. Click on the red line dividing the two images in the Main Image window.

    The Pair Inspection window opens showing an image from each of the cameras zoomed in on the overlapping border area.

  2. Mark several (approx. 5) tie points evenly distributed along the border of the images, using the following procedure:

    1. Identify a clearly recognizable landmark that appears near the top of the screen in the images from both cameras (i.e. in the overlapping region). 

    2. Click the image of the landmark in Camera 2. The marked point is indicated by a blue circle.

    3. Click on the identical location in the image from camera The marked tie points are indicated by a red circle in each image.

    4. Scroll down by clicking and dragging each image

    5. Identify additional tie points and mark them using the above procedure.
  3. Click Close.
    The  Main Image window is displayed  with the marked tie points indicated in blue on the image.

  4. Click Calibrate. 
    The system executes the initial calibration, stitching the images together. The number of calibrations done is shown as (1).
  5. Click Find tie points.
    The system identifies additional Tie Points and marks them on the image.

    The auto-generated tie points are marked as follows:
    1. Blue – Good Tie Points
    2. Pink – Acceptable Tie Points
    3. Red – Poor Tie Points
  6. Verify that the vast majority of auto-generated Tie Points are marked in blue.
    If there are a lot of pink and red markings, click undo on the top right corner of the screen to cancel the initial calibration, then click Render Panorama and return to step 3 of this procedure.
  7. Click Calibrate.
    The system executes an additional calibration, optimizing the quality of the image stitch. The number of calibrations is shown as (2).
  8. In the Calibration Profile field, select Tight from the dropdown menu.
  9. Click Find Tie Point
    The system identifies additional Tie Points and marks them on the image.
  10. Proceed to the next stage of the calibration procedure, Marking Lines.

4.4   Marking Lines (multi camera)

Marking lines involves identifying  clearly marked straight lines (i.e. lines that are known to be straight in reality, although they currently appear to be curved in the image) that run across the entire length and width of the playing field. Mark a series of points along each of the lines.
Use the following guidelines for marking the lines:
  1. Mark along a clearly defined edge of the line.
  2. In places where the line is not clearly visible (e.g. rubbed out), it is better to leave a gap between markings rather than approximating.
To mark lines for calibration:
  1. In the Calibration screen, in the Point Addition Type field, select Line Points from the dropdown list.
  2. Identify a line that runs horizontally across the entire playing field. Choose which edge of the line is most clearly marked.
  3. Mark several (approx. 20) Line Points evenly distributed along the entire length of the field, using the following procedure:
    1. Click on the Main Image Screen near the location of the far left end of the line.
    2. The Line Point Window opens for Camera 2.
    3. Click on a point at the edge of the line on the far left side of the field.
    4. Mark additional points at regular intervals along the line until you reach the far right side of the field.
  4. Click Add Line.
    The marked line is saved in the system. The points marked along the entire line are marked as locked (with a line through the middle), showing that the line has been completed.
  5. Identify a line that runs vertically down the middle of the field (e.g. the mid-field line) across the entire playing field. Choose which edge of the line is most clearly marked.
    To be effective, at least some segments of the line must appear in the images from both Camera 1 and Camera 2.
  6. Mark several (approx. 20, 10 for each Camera) Line Points evenly distributed along the entire width of the field, using the following procedure:
    1. Click on the Main Image window in an area of the image from Camera 2.
      The Line Point Window opens for Camera 2.
    2. Scroll up by clicking and dragging the image to view the top end of the line.
    3. Click on a point at the edge of the line on the far side of the field.

    4. Mark additional points at regular intervals along the same edge of the line.
    5. When you reach the edge of the screen, scroll the image down to view the next section of the line.
    6. Continue marking points at regular intervals along the line until you reach the near side of the field or until the line that you are marking stops appearing in the image from Camera 2.
    7. Click Close.
    8. The 
    9. Repeat steps b-f for Camera 1.
    10. The marked line is saved in the system. The points marked along the entire line are marked as locked, showing that the line has been completed.

7. Click Calibrate.

The system executes an additional calibration, optimizing the quality of the image stitch. The number of calibrations is shown as (3).
At this point when Show Points and Show Frames are selected, the Main Image should show a dense display of blue markings along the midline and locked markings for vertical and horizontal lines. 



4.5   Frame Calibration 


Frame Calibration defines the region of the image that is relevant to the game action. This enables the Pixellot Automatic Production algorithms to focus only on the relevant parts of the image. This procedure comprises the following elements:

  1. Defining the Field Region
  2. Panoramic Frame Adjustment

4.5.1  Defining the Field Region

The field region is the part of the image that shows the actual playing field. By inputting data about the size and shape of the field and identifying key points that define the borders of the playing field you 'teach' Pixellot where the playing field is located. This enables Pixellot to apply AI algorithms to the action on the playing field while disregarding off-field activity.

The Field Region is established by setting the ground points. This involves marking several key points that define the area of the playing field.
  1. For standard rectangular shaped courts/fields such as basketball, soccer, football etc. this is done by marking the four corners as well as the two points where the midline intersects with the sidelines, as explained in the Marking Ground Points section. (Soccer, Basketball etc.) 
  2. For Hockey this is done by marking points in the four end zone face off circles, as explained in Marking Ground Points (Hockey)
  3. For Basketball, in addition to marking the Ground Points, as explained in Marking Ground Points (Soccer, Basketball etc.), you must also mark the Basket Locations, as explained in Marking Basket Location (Basketball).

4.5.2  Marking Ground Points (Soccer, Basketball, etc.)

  1. In the Point Addition Type field, select Ground Points from the dropdown menu.

  2. Set the field shape and size, using the following procedure.
    Make sure that the correct sport type is displayed in the Top Command Bar. If you need to change the selected sport type, follow the procedure described in Starting the Calibration Procedure

    1. In the Field Size pane, in the Field Type field, verify that user-defined is selected (default).

    2. Verify that the Use Pre Configured Points checkbox is selected (default).

    3. Click Set Field Size.
      The Set Field Size window opens.
      The values are set by default based on the standard field size for the selected sport type. In some sports such as soccer the actual field size may vary.

    4. In the Field Length field, enter the length of the playing field (in meters).

    5. In the Field Width field, enter the width of the playing field (in meters).

    6. Click Close.

  3. Mark the six essential ground points in the following order: Far left corner, intersection of far sideline and midline, far right corner, near right corner, intersection of near sideline and midline, near left corner.
    The point that should be marked next is indicated by the purple dot in the Field Region Schematic Diagram.

  4. Mark each ground point using the following procedure:

    1. Click on the Main Image window in the area of the Ground Point (i.e. for the first Ground Point click on the far left corner of the field).
      The Ground Point Window opens. 
    2. Click on the image at the precise location of the Ground Point.
    3. If necessary, adjust the location of the marker by clicking Mark Last Point and using the keyboard arrows to move the marker.
    4. Click Close.
    5. Repeat the above procedure for each of the Ground Points following the order described above.

  5. Once all six points are marked, click Calibrate.
    The system executes an additional calibration based on the Ground Points. The image in the Main Image window may shift position. The number of calibrations is shown as (4).

  6. If the image shown in the Main Image window does not include the entire playing field, use the Panorama Adjustment controls to re-position the image so that the entire field is included in the image.

  7. Click Show Field Region.
    The Main Image shows the Field Region highlighted in pink. Verify that the marked Field Region corresponds with the sideline markings on the field and that the midline marker corresponds with the midline of the field.
     

  8. If the correlation is not perfect, click Unlock Rig location and then click do free calibration.
    If the correlation remains imprecise, contact your Pixellot Support Agent.

  9. Click Close.

  10. For Soccer, Football etc. Proceed to  Panoramic Frame Adjustment
  11. For Basketball, you must first mark the basket locations, as explained in Marking Basket Location (Basketball)


4.5.3  Marking Ground Points (Hockey)

1. In the Point Addition Type field, select Ground Points from the dropdown menu.
2. Set the field shape and size, using the following procedure.
Make sure that the correct sport type is displayed in the Top Command Bar. If you need to change the selected sport type, see Starting the Calibration Procedure.
a. In the Field Size pane, in the Field Type field, select hockey-nhl (for a rink with NHL dimensions) or hockey-int (for a rink with IIHF dimensions).
b. Verify that the Use Pre Configured Points checkbox is selected (default).
3. Mark the four essential ground points in the end zone faceoff circles in the following order: far left, far right, near right, near left.
4. Mark each ground point using the following procedure:
5. Click on the Main Image window in the area of the Ground Point (i.e. for the first Ground Point click on the far left face off circle). The Ground Point Window opens. 
6. Click on the image at the precise location of the Ground Point. Mark precisely on the tip of the outer bracket markings as indicated by arrows in the diagram below.




7.  If necessary, adjust the location of the marker by clicking Mark Last Point and using the keyboard arrows to move the marker.
8.  Click Close.
9.  Repeat the above procedure for each of the Ground Points following the order described above.
10. Once all four points are marked, click Calibrate.
The system executes an additional calibration based on the Ground Points. The image in the Main Image window may shift position. The number of calibrations is shown as (4).
11.  If the image shown in the Main Image window does not include the entire rink, use the Panorama Adjustment controls to re-position the image so that the entire field is included in the image.
12. Click Advanced.
The Advanced Options window is displayed.



13. Click Show Field Region.

The Main Image shows the Field Region highlighted in pink. Verify that the marked Field Region corresponds with the sideline markings on the field and that the midline marker corresponds with the midline of the field.
{screenshot}

14. If the correlation is not perfect, click Unlock Rig Location and then click Do Free Calibration.

If the correlation remains imprecise, contact your Pixellot Support Agent.

Click Close and proceed to Panoramic Frame Adjustment.


4.5.4  Marking Basket Location

For a basketball court, after marking the Ground Points as explained in the Marking Ground Points location section, (For Soccer, Basketball, etc...) Use the following procedure to mark the Basket Location.

  1. In the Point Addition Type field, select Basket Location from the dropdown menu.

    Make sure that the sport type that is selected is basketball. If basketball is not set as the sport type then the Basket Location option is not shown.
  2. In the Selected Basket field, select Left from the dropdown list.

  3. Mark the left basket using the following procedure:

    1. Click on the Main Image window in the area of the left basket.
    2. The Mark Left Basket Location window opens.
    3. {screenshot}
    4. Click on the image at the precise location of the basket hoop.
    5. A basket location is marked by a yellow rectangle.
    6. {screenshot}
    7. Verify that the entire basket is shown inside the yellow rectangle. If it is not, then click on a different location until the basket is marked correctly.
    8. Click Close.

  4. In the Selected Basket field, select Right from the dropdown list.

  5. Mark the right basket using the following procedure

    1. The Mark Left Basket Location window opens.
      {screenshot}
    2. Click on the image at the precise location of the basket hoop.
    3. A basket location is marked by a yellow rectangle.
      {screenshot}
    4. Verify that the entire basket is shown inside the yellow rectangle. If it is not, then click on a different location until the basket is marked correctly.
    5. Click Close.
  6. Once both baskets are marked, click Calibrate.
    The system executes an additional calibration based on the Ground Points. The image in the Main Image window may shift position. The number of calibrations is shown as (5).
  7. If the image shown in the Main Image window does not include the entire court, use the Panorama Adjustment controls to re-position the image so that the entire field is included in the image.
  8. Click Advanced.
    The Advanced Options window is displayed.
  9. Click Show Field Region.
    The Main Image shows the Field Region highlighted in pink. Verify that the marked Field Region corresponds with the area of the rink.
    {screenshot}
  10. If the correlation is not perfect, click Unlock Rig location and then click do free calibration.
    If the correlation remains imprecise, contact your Pixellot Support Agent.
  11. Click Close.

4.5.5  Panoramic Frame Adjustment

Adjust the frame of the playing field that is shown in the panoramic view. This determines the maximal area included in the image shown in the video output. It also determines what area is monitored by the Pixellot Automatic Production algorithms to identify relevant game action.

The goal of the Panoramic Frame Adjustment is to zoom the frame in as close as possible on the playing field without cutting off any relevant areas of the field. The Panoramic frame must include at a minimum.

  1. All four corners of the field
  1. A bit in front of the near sideline
  1. The height above the far sideline in which the ball may travel (e.g. approx. 10m for soccer, 3m above the backboard for basketball etc.), this varies greatly between sports
To adjust the panoramic frame:
  1. Click Show Frames  to show the red line down the middle of the Panoramic image.
    Use the Panorama Adjustment controls to implement the following procedures.

  2. Center the frame using the Right/Left buttons.

  3. Tilt the frame using the Roll Left/Roll Right buttons so that the red dividing line is perfectly vertical.

  4. Use the Zoom In/Zoom Out buttons to zoom the frame to include all four corners of the field.

  5. If to achieve this you need to zoom out to the point that the playing field (and required space above the far sideline) doesn't fill the frame from top to bottom, then adjust the distortion using the following procedure.

    1. Click Set Distortion.
      The Distortion window is displayed

    2. Verify that Wide Angle Distortion is selected (default).

    3. Enter a value for the distortion, estimating the required degree of distortion. See examples below.

      There is no fixed rule for determining the optimal degree of distortion. It varies depending on the field size, camera location, sport etc. It is recommended to experiment by making incremental changes in the value until you discover the optimal setting. 

      Examples of Distortion:
      0.0 - No distortion (i.e. near and far sidelines appear perfectly straight). When the frame is zoomed in, this is likely to cut off the near corners.

      -1.0 - Dramatic convex distortion (i.e. the near and far sidelines appear as convex arcs). When the image is zoomed in this is likely to cut off the near and far sidelines.


      Positive values of distortion cause the image to curve in a concave arc, which is not a useful configuration for this system.

      After entering a value that seems effective, click Close in the Distortion window.

    4. Re-adjust the Zoom and positioning so that the frame is properly aligned.

    5. Verify whether the selected distortion setting enables you to maximize the zoom without cutting off any relevant areas of the playing field.

    6. If necessary, repeat the above procedure adjusting the distortion until you find the optimal setting.

4.5.6  Finalizing Calibration

To finalize the calibration:
  1. Click Approve, in the top left corner of the screen.
    The configured Field Region is marked in pink. A confirmation window appears.
  2. In the confirmation window, click Yes.
    A second confirmation window appears asking if you would like to activate the settings by restarting the VPU.
  3. Click Yes.
  4. The VPU restarts using the new calibration settings.
    It may take a few minutes for the VPU to re-activate.

Once the calibration is complete, you need to configure the color balance to optimize the coloring of the image. This procedure comprises of two elements.

  1. Synchronizing image color
  2. Configuring the CCU

5.1  Color Balance UI Elements


The Color Balance screen contains the following UI elements:
  1. Navigation Tab – the main navigation for selecting various tabs in the Engineering Station UI.
  2. Top Command Bar – includes command buttons for selecting the sport type and controlling the Color Balance configuration procedure.
  3. Main Image Window – shows the full panoramic image of the field, as it was configured in the calibration procedure. Clicking on the image shows a zoom-in view of the selected area in the Color Balance window.
  4. CCU Controls – controls for adjusting the specific color control settings. Click and drag a button up or down to adjust the level of a specific parameter.
  5. Preset CCU Profiles – a list of preset CCU profiles.
  6. Color Balance Window – a zoomed-in view of the selected area of the Main Image. The RGB balance is shown for the selected point.

5.2  Configuring the Color Balance

5.2.1  Synchronizing Image Color

This procedure synchronizes the color of the images from the two cameras to create a seamlessly integrated image. 
  1. Open the Color Balance tab.
  2. Mark an oval shaped 'mask' around the red line dividing the two sides of the image. The mask should extend over the entire width of the field. Use the following procedure to mark the 'mask':
    If there is a significant defect (e.g. indentation) within the field region, it should not be included in the 'mask' region.
    1. Click Mask Marking
    2. Click on the Main Image window at the top of the Field Region near the red dividing line.

    3. Mark additional points following a clockwise direction, creating an oval shaped 'mask'.

  3. Click Approve.
    The color settings are saved.

5.2.2  Configuring the CCU

Set the CCU settings to optimize the image coloring. You can select a preset color profile that is appropriate for your sport type. You can also adjust specific color settings such as saturation, contrast or coloration.

To adjust CCU settings:
  1. In the Presets pane, select the desired color profile.

  2. In the CCU Controls pane, click and drag a button up or down to adjust the specific color setting.

  3. Click Approve CCU.

    The CCU settings are saved.





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