Colour Calibration of CCD Cameras for Machine Vision Inspection

Colour calibration of CCD cameras is essential for colour inspection systems based upon machine vision. A properly calibrated camera provides colour measurements that can be usefully compared with results from other suitably calibrated devices. Calibration ensures that maintenance or replacement of CCD cameras does not require re-establishing colour quality parameters.

Benefits of Using Calibrated Colour Cameras for Inspection

A colour CCD camera can be used to obtain detailed colour measurements for product quality assessment and control. Colour digital imaging is being applied in many areas such as food manufacture and timber and agricultural product quality assessment. However, an essential requirement for colour measurement with CCD cameras is that the cameras are calibrated to provide accurate and consistent colour measurements. The benefits of using a suitably calibrated camera are:

• Colour measurements and colour quality parameters have enduring value because they are related to objective standards.
• Separate imaging systems produce comparable colour measurements, allowing comparison of measurements made with separate systems. This makes it possible to ensure colour quality consistency between separate manufacturing sites.
• Colour quality parameters can be transferred between quality measurement facilities in conjunction with product transfers.
• Maintenance or replacement of components, especially the camera, does not affect colour measurements or quality parameters.

Techniques for Colour Calibration of CCD Cameras

Some colour calibration systems rely on matching one camera against another -- one camera is initially calibrated and other cameras are then calibrated to match the "master" camera. This approach can result in good short-term consistency between measurements made with separate systems, but cannot produce enduring quality parameters. When the "master" camera fails or its characteristics change, there is no longer a reference available for calibration of new systems. Drift in colour standards becomes inevitable.

A superior approach is to obtain independent but highly accurate colour calibration data for each individual camera. Hamey Vision Systems, in collaboration with the CRC for International Food Manufacture and Packaging Science, Access Macquarie Ltd. and Arnott's Biscuits Ltd., has developed a unique method of colour calibration for CCD cameras that provides colour measurements that agree to within 0.5% between independently calibrated cameras. This accuracy has been shown to be sufficient to obtain the benefits listed above, eliminating problems with colour quality measurement resulting from imaging system maintenance and product transfers.

Hamey Vision Systems: Experience with Camera Calibration

Hamey Vision Systems have integrated colour calibration into a system for assessment of biscuit bake colour quality. Deployment of this technology provided colour measurements with high agreement between separate systems. This made it possible, for the first time, to transfer colour quality parameters in conjunction with product transfers. We have also demonstrated that quality parameters are maintained when a camera is replaced with another calibrated camera.

The benefits of machine vision systems for colour measurement can only be fully realised with suitable colour calibration of the CCD camera. Contact Hamey Vision Systems today to discuss your needs for calibrated colour imaging.