User manual

Table Of Contents

Small Vision System User Manual 46

4.1 Calibration Procedure

An automatic calibration procedure using five image pairs of a planar calibration target is included as

part of the

smallv program. Given the image pairs of the calibration object, the system automatically

locates corner features in the target, fits a model of the target to the images, and finally produces an

estimate for the left and right camera intrinsics, the stereo head extrinsics, and the rectification matrices

, , , and H . These values are then used by smallv, and can also be saved as a parameter file

for later re-use. More information about the calibration procedure can be found in the Calibration

Addendum to the User’s Manual.

4.1.1 Calibration procedure steps

1. Create the calibration object. Print out a copy of the file data/check.pdf (Figure 4-1) and

paste it to a surface that is as flat as possible. We use a wooden cutting board as a backing surface

at SRI.

2. Start the

smallv application and start capturing video. It is recommended that you set the video

resolution to at least 320x120 in order to get enough detail of the calibration object. A calibration

computed when capturing video at a higher resolution can be used for future video captured at any

resolution with the same cameras.

3. Bring up the calibration window by pressing the

Calibrate… menu button. Fig. 4-4 shows the

calibration dialog window (the figure shows the dialog after an image has been captured and

processed).

4. Determine the appropriate characteristics of the camera imagers and enter them into the four boxes

in the middle of the dialog. If you have one of the Videre Design stereo heads, check the

appropriate box and the parameters are loaded automatically.

5. Acquire five stereo pairs of the calibration object at different rotations and translations. Try to

avoid views that differ by a simple translation, as they are less informative than views with

variation in rotation. As shown in Fig 4-4, there is a tab control that shows only one pair at a time;

choose a tab to select another pair. To capture the current video feed into a stereo pair box, simply

press the capture button. You can also save and load images to and from disk using the

load and

save buttons.

Figure 4-1 Checkerboard calibration object.