Camera Calibration Technical Report:
Hardware

Hardware

The image digitisation and analysis was performed on a Sun (Sun Microsystems) 3/160 computer fitted with a Primagraphics ``Virtuoso'' framegrabber (Primagraphics Ltd, Royston, Herts., UK). The video cameras tested and compared in this work were a Pulnix TM86 and a Sony XC-77CE, both of which are CCD array cameras. The camera was mounted on a Leitz Ortholux microscope fitted with a standard bright-field condenser and a $\times 10$ objective lens. The Primagraphics framegrabber was capable of digitising the full video image to a spatial resolution of 768x576 pixels and a grey-level resolution of 8-bits, i.e. values ranging from zero to 255. The microscope illumination was powered by a Roband ``Vareco 33-10'' DC power supply. It is particularly important that the lamp voltage should be stable for accurate densitometry. The theory outlined above assumes constant spectral charateristics of the light source. In practice this is very difficult to control therefore we use monochromatic light by inserting a narrow band-pass filter in the light path. For these experiments we have used a BALZER interference filter with measured response peaked at 563 nm (green). For the experiments described below we used a Kodak Wratten neutral density filter of OD 0.1.