The default settings in PhotoModeler are to calibrate and solve for the K1, K2, P1 and P2 lens distortion parameters. Some lenses will not require all these parameters to be solved and some lenses may require the addition of the K3 radial distortion parameter. This section describes how one determines the best set of lens distortion parameters.
• A wide angle lens (fisheye or high distortion) may require K3
• Good quality non-distorting lenses may not need K2 or K3, and
• Some telephoto lenses may not require P1 and P2.
The general approach is to calibrate the camera using the standard and default settings with the Automatic Processing Parameter Assignment and ‘Deviation and Correlation Check’ options turned on and then study the results:
• if the calibration processing fails and the lens is non-standard (telephoto or very wide angle) one should try reducing the parameters and rerun the calibration.
• if the deviation value for a parameter is larger than the parameter itself (see Project Status Report) then that parameter should be removed and the calibration rerun.
• if the camera parameters are very correlated (over 90% or 95%) (see Project Status Report) then they cannot be solved well independently and one or more of them should be removed and the calibration rerun. For instance, if K1 and K2 are highly correlated then remove K2.
• if the marking residuals are large (esp. the RMS residual (over 0.5 pixels)), all other possible errors have been taken into account, and it is a wide angle lens then K3 may need to be added.
Automatic Processing Parameter Assignment will automatically adjust the parameters that are solved if they are causing processing failure. Also, when the Deviation and Correlation check option is on, parameters that have high deviations or high correlations will be removed from the calibration automatically. Processing will be repeated automatically until a suitable calibration is solved. If you have either of these options turned off (or if a calibration fails after automatic adjustments) and if you want to manually experiment with calibration settings you can change which stages are completed and which parameters are solved during a Camera Calibration using the Camera Calibration Options Dialog.
Calibration uses two stages of processing. If you have Automatic Processing Parameter Assignment turned off, you can set which camera parameters to solve/calibrate in each stage on the Camera Calibration Options Dialog by selecting the processing stage in the drop down box at the top of the dialog. It is usually a good idea to allow PhotoModeler to do this automatically, but if you want to experiment with the calibration you should typically solve for the more basic parameters in Stage 1 (e.g. Focal Length, Format Size Width, Principal Point and K1) and the rest in Stage 2 (e.g. Focal Length, Format Size Width, Principal Point, K1, K2, P1, P2, and sometimes K3). Once these changes have been made, the calibration can be run or rerun.
When comparing calibrations to determine which is better you will study values found in the Project Status Report and compare:
• Parameter deviation values - the calibration with smaller values is better
• Parameter correlations - the calibration with no correlations between parameters is better (or significantly lower correlation values)
• Marking residuals (largest and RMS) - the calibration with significantly lower RMS marking residual is better.
If you need further assistance do not hesitate to contact your seller for support.