Camera parameters for different resolution

Hardware ZED2
1

Hi,sir

I’m using ZED 2i to do stereo camera calibration and depth measurement . Here is my idea:
I catch the raw image, calibrate the stereo camera myself, compare the calibration result with your calibration file, and use this parameter as the basis for depth measurement, but I have problems in the calibration stage and have not yet moved to the next step.

If set the resolution to HD720, then I should get the corresponding values under [LEFT_CAM_HD] and [RIGHT_CAM_HD] in the SN file, right?

When I get the camera parameters from your SDK, the results do not seem to correspond to the parameters under HD720, why? And how should I do?

Here is my code :

Camera zed;

InitParameters Init_Para;
Init_Para.camera_resolution = RESOLUTION::HD720;
Init_Para.camera_fps = 15;
Init_Para.depth_mode = DEPTH_MODE::ULTRA;
Init_Para.coordinate_units = UNIT::MILLIMETER;
Init_Para.camera_disable_self_calib = true;

ERROR_CODE returned_state = zed.open(Init_Para);
if (returned_state != ERROR_CODE::SUCCESS)
{
  std::cout << "Error " << returned_state << ", exit program." << endl << endl << endl;
  return EXIT_FAILURE;
}

while (i < 5)
{
  if (zed.grab() == ERROR_CODE::SUCCESS)
  {
   zed.retrieveImage(Left_image, VIEW::LEFT_UNRECTIFIED);
   zed.retrieveImage(Right_image, VIEW::RIGHT_UNRECTIFIED);
   auto timestamp = zed.getTimestamp(TIME_REFERENCE::IMAGE);
   Left_image.write((Left_Image_Directory_name + "\\" + to_string(timestamp) + ".png").c_str());
   Right_image.write((Right_Image_Directory_name + "\\" + to_string(timestamp) + ".png").c_str());

   i++;
   }
 }

CameraParameters Camera_para_left = zed.getCameraInformation().camera_configuration.calibration_parameters.left_cam;
CameraParameters Camera_para_right = zed.getCameraInformation().camera_configuration.calibration_parameters.right_cam;


//the changing code,and the ohter code is remained
CameraParameters Camera_para_left = zed.getCameraInformation().camera_configuration.calibration_parameters_raw.left_cam;
CameraParameters Camera_para_right = zed.getCameraInformation().camera_configuration.calibration_parameters_raw.right_cam;


cv::Mat DistortionL(8, 1, CV_64F);
//k1,k2,p1,p2,k3
DistortionL.at<double>(0, 0) = Camera_para_left.disto[0];
DistortionL.at<double>(1, 0) = Camera_para_left.disto[1];
DistortionL.at<double>(2, 0) = Camera_para_left.disto[2];

//the other distortion parameters... ...
//my calibration......

the result is:

image
image349×527 2.98 KB

and the changing code result is:

image
image337×528 5.83 KB

Some values ​​of the SN file are as follows：

[LEFT_CAM_HD]
fx=534.59
fy=534.455
cx=632.085
cy=356.9815
k1=-0.0680342
k2=0.0484897
p1=-0.000230024
p2=0.000412872
k3=-0.0191863

[RIGHT_CAM_HD]
fx=533.31
fy=533.135
cx=623.805
cy=357.3375
k1=-0.0708259
k2=0.0545271
p1=-0.000345875
p2=-9.04287e-05
k3=-0.0228891

[LEFT_DISTO]
k1=-1.29351
k2=2.42123
k3=0.174327
k4=-1.19905
k5=2.26309
k6=0.340436
p1=-0.000353254
p2=7.36605e-05

[RIGHT_DISTO]
k1=-1.49879
k2=2.89675
k3=0.0692749
k4=-1.40798
k5=2.74192
k6=0.242784
p1=-0.000280535
p2=0.000144192
2

Hi @hhp
Welcome to the Stereolabs community.

This is not always true. The calibration file stores the RAW camera parameters.
The ZED SDK when opening the camera performs a quick recalibration, so the raw parameters can slightly change.
You can disable this behavior: see camera_disable_self_calib

This is expected for what I’ve written above, and if you use the wrong API to retrieve the camera parameters

You are indeed retrieving the parameters of the rectified images (distortion parameters are 0.0).

You must use calibration_parameters_raw instead of calibration_parameters to retrieve the raw parameters.

3

Hi, @Myzhar

I’ve been disable the selfcalibration here.

//the changing code,and the ohter code is remained
CameraParameters Camera_para_left = zed.getCameraInformation().camera_configuration.calibration_parameters_raw.left_cam;
CameraParameters Camera_para_right = zed.getCameraInformation().camera_configuration.calibration_parameters_raw.right_cam;

And I have also tried using [calibration_parameters_raw], but the result is the second picture, which is the [LEFT_DISTO] and [RIGHT_DISTO], not the [LEFT_CAM_HD] and [RIGHT_CAM_HD]

So should I do to get the raw parameters for the resolution of HD720?

4

Distortion parameters are the same for each resolution.
Only focal and biases values change.

The values seem to match the values of the conf file.
Where do you see differences?

5

If the distortion parameters are the same for each resolution, what do the parameters k1、k2、p1、p2 and k3 under CAM_HD in the SN file mean?

6

They are used internally. You can ignore them

7

thanks for your kind.