Projector Calibration Manager

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Projector Calibration Manager

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Navigation:  Widget Designer > Tools >

Projector Calibration Manager

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The Projector Calibration Manager is a Tool that allows to setup the connection between a Calibration Link and other Pandoras Box software components. It is a fundamental item in the entire Re-Calibration process.

The principle behind "Re-Calibration"

Currently only projections onto 2D-planes can be re-calibrated. The automation for 3D structured screens will follow. However, the general principle behind the calibration applies to any screen shape.
The fibre cable ends are mounted into the screen in the below described way. Then the projector setup is done as usual, followed by the warping or keystone step and / or softedge. Now, the image fits onto the screen. After a while, this might not be the case anymore, because the projector or the screen have moved. A typical scenario is a lamp change for a projector in a fixed installation. It is important that the projector still covers about 90% of the screen area. At least the projector needs to hit all calibration points.
This is when the Calibration Link is used as the screen- /projector-shift can be evened out with an automated re-calibration. This works with fiber cables measuring the light from the projector which projects different testpattern. The process does not include any cameras, only fibre cables and the Calibration Link. Based on these light measurements, the exact pixel location can be determined and necessary changes can be applied (automatically) to Pandoras Box software.
In short, the re-calibration is not an automated warping for the first setup. Once the projectors are setup by a technician who knows the system but a projector- or screen-shift has occurred, the re-calibration allows anybody to adjust the new output offset within a couple of minutes. The entire process can be started with one button click and no further manual settings are necessary. This is useful when the installation is serviced by staff who does not know how to reset the warp and blend properly.

The pixel accuracy that can be achieved in a best case scenario is 1mm / +- 1pixel accuracy.

There are different modes for both, 2D and 3D re-calibration, some are restricted to Server features whilst others are accessible for Pandoras Box Player as well.

Currently, the calibration points are fibre tips. However, in the near future, they can be alternatively replaced with markers or digital markers seen by cameras.

Mounting the fibre cables

The Calibration Link is a device that allows to measure the light intensity levels of a 1mm fiber cable. The Re-Calibration process is based on these measurements. Hence, the quality of light transmission effects the quality of the process significantly.

The cable ends are mounted into the screen in a way that the fibers "look" straight at the projector to catch as much light as possible. The more offset the cable ends have, the more precise the calibration can be. At best, they are mounted into the corners.
A minimum number of four cables is required per projector. However one can be shared by several projectors. That is, if you have a softedge blend with two projectors then you can use six fiber cables (two in the overlap, and the other four near the corner of the screen).

Direct sun light needs to be avoided. By the very nature of the cables, they should be bend as less as possible. Also, the fibre cables that form a group for one projector should be equally long. The minimum length depends on the brightness of the projector. The longer the fibre cable is, the more light needs to hit the tip of the cable. As a rule of thumb, a 10m fiber cable requires at least 100lux. If you have 20m cables then you need to have a minimum brightness of 200lx and so on.

The cable ends must be clean and cut as straight as possible. It is highly recommended to use a professional fibre cutter to do so as other tools squeeze the fibre and reduce the transmission quality. Neither end from the glass itself must stick out from the cable sheath! Simply hold to isolated end into the fibre input and move slightly forwards until it withstands, then tighten the screw-able input.

It is recommended that the projector pixels are in a best focus position for all fiber points.

Hardware and software setup

This depicts the communication between Pandoras Box (PB) components, Widget Designer (WD), Calibration Link and fibre cables.

First of all, a PB Master (e.g. a Manager) is connected with a PB Client (Server or Player) or a Server / Player run in stand-alone mode. The PB Menu runs in the background of the PB Client. Widget Designer may run on the same or a separate hardware and is connected to the PB Master and the Calibration Link. Fibre cables run from the Calibration Link to the screen and detect light from a projector that is connected to the PB Client.

1. The user starts the re-calibration process by clicking a button in WD.
2. WD tells PB Client via network to leave fullscreen.
3. WD tells PB Menu via network to start slide show of calibration testpattern.
4. Each testpattern is shown by the projector(s).
5. According to their position, the fibre cables receive a certain light amount per each testpattern.
6. The Calibration Link measures the light amount and transmits that information via network.
7. WD calculates the position from the fibre tips (markers) based on the light measurements for each testpattern.
8. WD calculates the necessary re-calibration settings.
9. WD applies the changes to the PB Master (via network). The changes are defined by the chosen mode:
 a) WD calculates and applies new parameters for the Camera layer.
 b) WD creates and applies a new warp object for the Output layer.
10. WD toggles the PB Client into fullscreen mode. The re-calibration process is finished within a few minutes.

Software components

The following software components are needed and should be connected to each other:
- a running Pandoras Box Master with Camera Layer / Output Layer settings for the Client
- a running Pandoras Box Client
- a running PB Menu on the Client
- for some modes, an installed Warper on the Client
- a running Widget Designer project with the following two nodes and a tool

Create > Nodes > Input > Devices > Calibration Link - one node per Calibration Link device
Create > Nodes > Input > Pandoras Box > PB Menu - one node per Client
Tools > Projector Calibration Manager


In the Projector Calibration Manager "Add a new Output" and the according "Edit" dialog opens. Each projector is to be managed individually. If you like to open the Edit dialog, simply double-click on an existing entry.



Item ID
The internal ID cannot be edited.

Choose a name for the output.

Menu Node ID
Enter the Node ID from the PB Menu node. Within the node itself, the IP address from the Client must be entered.

Output Mode
Choose the according output mode according to the Client's graphics card settings.

Output Preset and Resolution
Choose the resolution per output according to the Client's graphics card settings. You may use the preset list or enter a custom (pixel accurate) custom resolution.

Calibration Mode
Choose the calibration mode you wish to use.

2D Screen Offset (implemented and tested) - This mode the most simple one. It modifies the X & Y offset parameters in the Output Device Layer in the Master software to offset its warp object. The changes are based on the average offset of the projectors original home position and its new position. No scaling or rotation is applied in this mode.

2D Planar Perspective (implemented and tested) - This mode opens the defined warp file and modifies the mesh according to the projector changes (X & Y offset, rotation, size and perspective transformation). A new warp file is being generated, saved under the given name and applied to the output in the Master software.

3D Planar Calibration - (for future use) - This mode will use the 2D planar calibration method of Pandoras Box Warper. In this case the fiber points and the 4 coplanar (!) markers must match. The result of this process is that a new Camera Position will be calculated and applied in the Pandoras Box Master.

3D Object Calibration - (for future use) - This mode will use the 3D pose calibration method of Pandoras Box Warper. In this case the fiber points and the 4 non-coplanar (!) markers must match. The result of this process is that a new Camera Position will be calculated and applied in the Pandoras Box Master.

This interval determines the calibration image update rate. The default value is 200ms and can be increased when the network performance does not allow to change the calibration images that fast.

Warp and X File
Depending on the chosen Calibration mode, you are asked to name a Warp and X file. Click the [...] icon to choose the file directory on the Client. For the X file, please enter the File and Folder ID used in the Pandoras Box Master.
The Import Markers button is for future use.

PB Camera and Output ID
Depending on the chosen Calibration mode, select the Site and Device ID (as seen in the PB Master's Devices tab) for the camera or output layer.

Device Type
For future use. The current Re-Calibration process is based on the Calibration Link's measurements. Later, a camera-based process will be possible too.

PB Camera and Output ID
In order to get the home position data, a first initial calibration routine is required to calculate the pixel position of each fiber point per projector.

Calibration Point List
Create an entry for each Calibration point i.e. fibre tip. The order does not matter.
ID - the ID from the Calibration node
Input - the input from the Calibration device to which the cable is attached
Marker - the ID from a Marker in the Warper (only necessary for some Calibration modes)
Max: the maximum allowed brightness value as seen in the Calibration node's properties. The default value is 1024 and can be reduced to your expected value for a white pixel. If then a value above the maximum is measured, you know, that something unexpected occurred during the calibration process, e.g a moving light hit the screen.
Threshold - the minimum value difference between "white" and "black". Note that lowering the threshold might result in entirely wrong re-calibration results due to misinterpretations. Due to light noise, the default threshold of 50 is reasonable. Please read below passage "Possible error messages".

X, Y - The stored X and Y position per calibration point after the button "Store Home Position" was clicked. You may modify the number by clicking in the field and typing.

X', Y' and Z' - The new X, Y and Z position per calibration point after the button "Re-Calibrate and Apply" was clicked.

number  It is important to note that the physical fiber point location should not be changed after the home position has been initialized and stored.

Store Home Position
The process to find the home position is done by projecting a series of black and white horizontal and vertical images. This process takes minimum 30 sec per projector (the time depends on the systems signal latency and network speed). As a result the X and Y positions are stored in the above described Calibration Point List.

Re-Calibrate and Apply
The re-calibration process is done in the same way as finding the "Home Position". As a result the X', Y' and Z' positions are stored in the above described Calibration Point List. Depending on the chosen Calibration Mode, the necessary changes are calculated and applied.

Possible error messages

To find a "Home Position" or "Re-Calibrate Position" a series of black and white horizontal and vertical images is projected. With pure logical combination Widget Designer then determines where the fibre tip is located.
0,0 is the X and Y pixel position for the left upper corner. 1920,1080 would be the right bottom corner for an HD projector.
This entire process requires that "white" and "black" can be clearly distinguished. The above mentioned "Threshold" parameter in the Calibration Point List defines this minimum value difference.

If the minimum is not reached, the Calibration process fails and gives an according warning. Possible reasons why a black pixel cannot be distinguished from a white one could be that black is too bright or white is too dark or even black equals white:
- too much (side) light on screen that raises the value for black
- broken projector lamp
- poor cable transmission quality
 - broken Calibration Link
 - broken cables
 - too long cables
 - cables bend
 - cable tips dusty, dirty
In the worst case, the projector moved so much that its light does not hit the fibre tips any more. So before starting the process, ensure that the projector covers all of its related fiber points as well as all of its dedicated screen-space.

The minimum values in the Calibration Link node for white should be above 100, for black 30-40 and most importantly, the difference between white and black should be around 30-120.
If your value for white exceeds 1024 you may set the Calibration Link to coarse mode. It roughly doubles the value range. If you need to do that, open the Calibration Link and find a dip switch on the circuit board. If you need assistance, please contact coolux support.