Camera Accuracy: Guidance on Camera Intrinsic Parameter Correction

Problem Description

Some cameras on-site experience problems including intrinsic parameter deviations due to environmental changes or prolonged usage and picking errors after stable operation. If the scalar difference exceeds the factory standards by a significant margin (more than 50%), you can quickly correct the camera’s intrinsic parameters to avoid sending the camera back to the factory and address on-site issues more promptly.

How to Use Intrinsic Parameter Correction Tool

This tool is used to check the accuracy of intrinsic parameters, correct intrinsic parameters, and restore factory intrinsic parameters. Only when the intrinsic parameters are accurate can the calculated coordinates of various points be precise. Currently, the primary function being utilized is the intrinsic parameter correction.

Preparation

Before checking the intrinsic parameters, please ensure you have the accompanying calibration board.

Place the calibration board within the field of view and capture both the 2D image and depth map of the board. Make sure that the captured 2D image and depth map meet the following criteria:

  • The area where the circles are located on the calibration board is fully captured.
  • The 2D image is neither too bright nor too dark, ensuring clear and complete circles on the calibration board.
  • The grayscale values of the corresponding LSR L/LSR S/DEEP color image channels are between 180 and 255.
  • The circles on the calibration board are fully visible in the depth map.

Examples of 2D images of the calibration board:

Image too dark, the circles on the calibration board cannot be easily discerned. Circles on the calibration board are complete, and circle boundaries are clearly visible. Image too bright, the circles on the calibration board cannot be easily discerned.
image imageimage image

If the obtained 2D image does not satisfy the requirements, please adjust the parameters for the 2D image.

Examples of depth maps of the calibration board:

Exposure time too short, the circles on the calibration board are incomplete. Circles on the calibration board / the entire calibration board are complete. Exposure time too long, some or all the circles on the calibration board are lost.
image imageimage image

If the obtained depth map does not satisfy the requirements, please adjust the parameters for the depth map.

Checking Intrinsic Parameters

Click on the Tools menu in the menu bar, select Intrinsic Parameter Tool, and enter the Intrinsic Parameter Tool window.

When checking intrinsic parameters using the Intrinsic Parameter Tool, please follow these steps:

  1. In 1. Place calibration board and check image quality, click Acquire images to obtain the 2D image and depth map of the calibration board. Check if the images satisfy the requirements.
  2. In 2. Select calibration board model, set the specifications of the calibration board:
    • If using a standard calibration board model, click the small triangle on the right to select the calibration board model.
    • If using a custom calibration board, select Customized, and then set the model, rows, columns, and spacing based on the information provided.
  3. In 3. Check intrinsic parameters, click on Check intrinsic parameters to start the inspection. After the check is complete, a pop-up window displaying the inspection results will automatically appear.
    • If the intrinsic parameter check results in the pop-up window show green data, the intrinsic parameters are valid, and the tool can be used normally.
    • If the intrinsic parameter check results show red data or there are other error prompts in the pop-up window, there is a significant intrinsic parameter error, or the check is not passed. Please follow the prompts in the pop-up window to resolve the issue.

For projects with high accuracy requirements, you can use the high-accuracy mode: switch to the Administrator account, in Intrinsic Parameter Tool, check High-accuracy mode in 3. Check intrinsic parameters, and place the calibration board according to the displayed distance. If the calibration board is not placed at the designated distance, the intrinsic parameter check may fail.

Troubleshoot Common Problems

The following issues may be encountered while checking the intrinsic parameters.

Errors in the Intrinsic Parameters Are Large

Symptom:

The intrinsic parameter check results are displayed in red, indicating that the errors in the intrinsic parameters are large.

Solution:

Please try the following solutions:

  1. Check if the calibration board specifications are correct.
    • If incorrect, enter the correct specifications. Then, check the intrinsic parameters again.
    • If correct, proceed to the next step.
  2. Check if the 2D image and depth map meet the image requirements. Please refer to the image requirements.
    • If the 2D image does not satisfy the requirements, please adjust the parameters for the 2D image. If the depth map does not satisfy the requirements, please adjust the parameters for the depth map. Then, check the intrinsic parameters again.
    • If the images satisfy the requirements, proceed to the next step.
  3. Use the Correct intrinsic parameters function to correct the intrinsic parameters. Please follow these steps:
    1. Place the calibration board within the camera FOV.
    2. Check the Correct Intrinsic Parameters option, and then click Acquire data.
    3. Move the calibration board, and click Acquire data again.
      • Note: The calibration board used here must meet the following requirements:
        1. The board’s height should generally fall within the camera’s working area, positioned near the bottom at approximately 1/3 of the total height, as illustrated in the diagram below:
          :red_square: : Camera Working Area
          :blue_square: : Camera Projection Range
        2. Please provide a minimum of five sets of calibration board poses. Ensure that the board is placed horizontally without any upward tilt. The fundamental placement requirements are as follows:
          :red_square: : Camera Working Area
          :blue_square: : Camera Projection Range


          :point_up: From left to right: Center, Upper Right Corner, Lower Right Corner, Upper Left Corner, and Lower Left Corner.
    4. After adding the data, click Correct intrinsic parameters. When the correction is completed, a window of the correction results will pop up.
      • If the correction succeeded, click Check intrinsic parameters in this window to check the intrinsic parameters again.
      • If the correction failed, click Confirm in this window, and retry the correction or contact Technical Support.

Circles on the Calibration Board not Detected

Symptom:

The intrinsic parameter check result window displays this message: Circles on the calibration board not detected.

Solution:

Please try the following solutions:

  1. Check if the calibration board specifications are correct.
    • If incorrect, enter the correct specifications. Then, check the intrinsic parameters again.
    • If correct, proceed to the next step.
  2. Check if the 2D image and depth map meet the image requirements. Please refer to the image requirements.
    • If the 2D image does not satisfy the requirements, please adjust the parameters for the 2D image. If the depth map does not satisfy the requirements, please adjust the parameters for the depth map. Then, check the intrinsic parameters again.
    • If the images satisfy the requirements, proceed to the next step.
  3. Use the Draw aid circle to facilitate the detection. Please follow these steps:
    1. In 3. Check Intrinsic Parameters, click Draw aid circle.
    2. Find a complete circle on the calibration board in the 2D image. Click while holding the Ctrl key and then move diagonally up or down to adjust the size of the aid circle. Click again to finish drawing the aid circle.
      • Only one aid circle can be drawn. The aid circle should be as close possible to the boundary of the circle on the calibration board.
      • If you need to re-draw the aid circle, click Draw aid circle again.
      • To zoom the 2D image, move the cursor onto the 2D image and scroll the mouse wheel.
    3. In 3. Check Intrinsic Parameters, click Check intrinsic parameters to check the intrinsic parameters again.
      • If the check succeeded, the troubleshooting has been completed.
      • If the intrinsic parameter check result window still displays Circles on the calibration board not detected, proceed to the next step.
  4. Use the Edit Feature Detection Parameters function to facilitate the detection. Please follow these steps:
    1. In 3. Check Intrinsic Parameters, click Edit Feature Detection Parameters (Advanced).
    2. Adjust the displayed feature detection parameters according to the actual situation.
    3. If not all the circles on the calibration board can be captured, check Allow absence of some circles, and adjust the newly displayed feature detection parameters.
    4. In 3. Check Intrinsic Parameters, click Check intrinsic parameters to check the intrinsic parameters again.
      • If the check succeeded, the troubleshooting has been completed.
      • If the intrinsic parameter check result window still displays Circles on the calibration board not detected, please contact Technical Support.

Valid Feature Points Not Found in Depth Map

Symptom:

The intrinsic parameter check result window displays this message: Valid feature points not found in depth map.

Solution:

Check if the depth map satisfies the requirements. Please refer to the image requirements.

  • If the depth map does not satisfy the requirements, please adjust the parameters for the depth map. Then, check the intrinsic parameters again.
  • If the depth map satisfies the requirements, please contact Technical Support.

Intrinsic Parameter Tool: Failure to Restore Normal Parameters

In the case of extreme situations, if the intrinsic parameters remain abnormal even after using the Intrinsic Parameter Tool, please contact technical support. If the camera has a significant intrinsic parameter deviation that cannot be resolved through calibration, it may be necessary to return it to the factory.

Extrinsic Parameter Calibration Setup After Intrinsic Parameter Calibration

Following the calibration of the camera’s intrinsic parameters, it is essential to reset the camera the compensation parameter values offset to a unit matrix before proceeding with extrinsic parameter calibration. During extrinsic parameter calibration, ensure that the option for Recalculate compensation parameters is unchecked. With this step, the camera calibration process is complete.
image