Camera Calibration Technical Report:
Discussion and Conclusion

Discussion and Conclusion

The two images shown in figure 4 were obtained with two different cameras which were found to have very different response functions. The calibration technique descibed in this paper has been applied in each case using in-house software and takes about three minutes for each camera. Once calibrated then by capturing a bright field image it is possible to estimate the true optical density on the slide although in this case we have not corrected for glare. The corrected images for both cameras shown in figure 5 illustrate how well the method works. There are differences between the images arising from digitisation artefacts and as explained earlier it may be advantageous within any particular application not to set the camera to respond linearly with respect to intensity.

In many applications, for example the determination of cell ploidy, it is important to increase the density resolution at the dark end of the scale and so choosing $\gamma \approx 0.5$ provides better resolution of the objects of interest.

In summary we have developed a convenient and accurate technique to calibrate video cameras for microscopic applications. The method relies only on the definition of optical density and can be applied to any camera with any response function, in particular it is not necessary to assume linearity. The only additional equipment requirement for a digitising system is a single neutral density filter and the calibration can be undertaken using typical slides for any application.

The authors would like to acknowledge and thank Mr Steve Farrow for many useful discussions on the subject of camera calibration.