User Manual Pages

Camera Calibration

Before you can scan objects, you have to calibrate the camera. The following steps will guide you through the camera calibration dialog of DAVID:

Make sure that the camera is connected to the PC and that the camera drivers are installed. Your camera must support WDM Video Capture Driver (i.e. DirectShow-Driver) for Windows.
Click on the upper rollout-box and choose your camera device. If your camera is not listed, try to reconnect it and open the rollout-box again. After you have chosen a camera device, you will be asked whether you want to allow DAVID to read and write camera parameters (description). This function greatly enhances comfort by remembering and switching between different camera settings for calibbration, scanning, and texture grabbing. Therefore it should be switched on - unless problems appear. Finally, a new window with a camera live view appears.
If the standard image format (e.g. resolution or frames per second (fps)) does not match your requirements, you can change the image format by pressing the “Change Format” button.
Place your camera in front of the calibration corner (see here for a construction manual), in such a way that the calibration pattern is completely visible in the camera image. The automatic camera calibration approach needs an image with a high contrast. (Usually the calibration points are black and the background is white. If you have bright points on dark background, check the “Inverted printout” option.) To get an adequate contrast, you have to adjust the camera setting (by pressing the “Camera Settings” button and/or switching on a light source). An optimal camera image looks like this:

Besides the 25 calibration markers, there should not be any too dark objects (image areas) in the camera image!

Usually you can skip step 5.
a) OPTIONAL: Use the Eraser to improve your calibration image! If the calibration fails in automatic mode, look at the error message. Often DAVID has found too many markers. You can easily help DAVID by selecting the “Eraser” calibration mode. The “size” refers to the size of the rectangular mouse eraser. Use your left mouse button to “clean” the camera image from false markers (dark image areas). You can “unerase” with the right mouse button. The following screenshots show a not-optimal calibration image where the user has erased dark areas (bright white):

b) ADVANCED: Manual calibration mode (not recommended)
If you have a very difficult environment where even the Eraser Mode does not help, you can define the marker positions manually. Select the manual mode. Use your mouse to define the calibration points:
- Left mouse button: Select a marker (click) or move the selected marker (press and hold).
- Right mouse button: Add a new marker (behind the selected marker)
- Middle mouse button: Remove selected marker.
  The order (0-24) is important! It must be like shown in the following image:
  
  You must position the markers precisely in the middle of each marker.
Assure that the scale of your printed calibration pattern is correct. The value in the input field labeled “Scale (mm)” and the distance (in mm) between the centers of two printed calibration points should match perfectly.
Press the “Calibrate Camera” button . If the camera calibration is successful, you should see small red crosses in the live image, which mark the centers of the calibration points:

If the calibration failed , first try to readjust the camera image (aperture, exposure time, light conditions). Use the Eraser Mode to clean “dirty” areas so that the 25 markers are the only dark image elements.(see steps 4 and 5).The calibration failure message should help you to find the problem.
Press “Next” button to enter the scanning dialog.