Calculate calibration parameters

Calibration-Set Manager

Clicking on the button "Calibration Set Manager" on the main form or alternatively on File >> Calibration Set Manager opens following window:

The Calibration Set Manager manages the Calibration Sets of the different cameras respectively camera-lens-combinations. If an entry is selected, apart from the camera and lens designation also the corresponding distortion values are displayed, which give information about the distortion extend before and after calibration parameter application.

Because these values are not reliable with downloaded Calibration-Sets, they are displayed in gray in this case.

Residue distortion

By re-application of the produced calibration parameters to the point positions, which were determined from the Calibration-Pictures, a parameter accuracy estimation can be made. Accordingly the residue distortion information only applies to corrections in the captured focal lengths. Thus no statement can be made about the residue distortion for interpolated focal lengths.

The residue distortion reliability for the HQ-mode is quite high, since a variable safety factor was added here. The residue distortion is indicated higher, if for instance only one Calibration-Picture has been evaluated for the appropriate focal length. If on the other hand multiple Calibration-Picture are used, on which slightly different views of the Calibration-Map are visible, the residue distortion approximates to a smaller value.

In the LQ mode however no safety factor is added. The indicated value is a minimum value and therefore the real residue distortion is somewhat larger in all probability.

Interpretation of residual distortion

Using the high quality Calibration-Map usually the average residual distortion after HQ-mode calibration approximately amounts 0.1 pixels and the maximum residual distortion approximately amounts 0.5 pixels (with a camera with a resolution of approximately 4 megapixels).

If a lower quality Calibration-Map is used, where the points are not arranged accurately for example due to a lack of flatness, the residue distortion is accordingly higher in the HQ-mode, since ImageIron presupposes an optimal and thus plausible point arrangement on the Calibration-Map.

In contrast to the HQ-mode, in the LQ-mode neither the radial asymmetrical, nor the tangential distortion is removed. Assumed, the used camera would contain lenses, which have an ideal, to the optical axis symmetrical, surface, and assumed, these lenses and the optical chip would be ideally aligned, then the residue distortions would be equal in HQ- and LQ-mode. Since cameras and lenses in actuality show manufacturing inaccuracies however, the residue distortion values of HQ- and LQ-calibration differ from each other. The higher the residue distortion is in the LQ mode in contrast to the HQ mode, the more inaccurately the lens respectively the camera has been manufactured.

Calibration-Set Manager features

Create new / edit Calibration Set

The Calibration-Pictures form the basis for the calibration parameter calculation. Use the button Add Calibration-Pictures ... to add them to the list in the currently opened tab. If particular pictures shall be removed, select them in the list and click Remove selected Calibration-Pictures.

If the Calibration-Set shall not be created for a shift-lens, it is only allowed to append the list under the tab Shift = 0.

In order to reach a satisfying Calibration-Set build result, it is required that the Calibration-Pictures are not preprocessed and are available in (original) landscape format.

The calculation is started with Calculate calibration parameters.

Before the form is closed with OK, the new Calibration Set can be named with a user postfix (upper text box), in order to enable unique identification.

The Calibration-Sets will be available on the next application start and just need to be exported with Save for backup purposes. The data is filed in the user´s application-data folder.

It is recommended to keep the used Calibration-Pictures since ImageIron probably will be upgraded with further correcting functions, for which the Calibration-Pictures are probably required again.