Image processing
- the more mega pixels the better the quality?
The widespread use of image processing systems for the inspection of products has developed into a real race to incorporate the latest technical advances. Production lines are updated with mega pixel chips and gigahertz computers in an effort to bring an end to complaints.
Many of us have already learnt in other areas that it is not only the technical specifications which count. Those of us who have bought a digital camera with 4 mega pixel in the past have often realized that a high resolution does not always guarantee good pictures. By comparison a camera with a lower resolution but a superior lens can sometimes produce better results. Word has also got round in the computer world that a gigahertz computer alone is no guarantee for effective operation. The capabilities of a modern computer can only be used efficiently with the correct combination of many hardware components and the corresponding software.
This also applies to inspection technology. The correct combination of illumination, lens, camera and image processing is decisive for the inspection result.
When HEUFT SYSTEMTECHNIK GMBH were considering the further development of their inspection technology using CCD cameras technical specifications were not at the top of the list but the aims resulting from the user´s requirements:
- optimum detection quality combined with
- a low false rejection rate
- an insensitivity towards changes to the ambient conditions
- minimum maintenance
It quickly becomes clear that a higher resolution is only of secondary importance in order to achieve these goals when bearing in mind that HEUFT was already working with resolutions ranging up to 0.2 mm/pixel at the beginning of the nineties. Visible fault sizes are quickly detected with this but also production faults which are within the manufacturers´ permissible tolerances for packaging materials such as bottles, closures, labels etc. Consequently a completely different aspect came to the fore - image processing. In this case it is important to make the time available for each product to be inspected to permit sufficient calculations to be carried out for the fault analysis in order to decide whether this is a fault or a permissible tolerance in the manufacturing process.
It was possible to base the new HEUFT reflexx image processing technology on an important advantage of the HEUFT SPECTRUM TX series. In contrast to PC-based inspection systems the processing speed is independent of other system components due to the separation of operating surface and inspection system. In other words: each module only carries out the work for which it was designed. The image processing card deals exclusively with the processing of data supplied by the camera. This structure guarantees high speed and maximum reliability and stability for the system. Data inquiry via the production data acquisition or additional access via a remote terminal e.g. from the foreman´s office do not influence the inspection accuracy. Even if the operating surface fails, which hopefully will never happen, the inspector will still continue to detect faulty products and reject them.
The second important difference to the systems of other competitors is the complete development of the hardware and software for the image processing . The answer to the question "what should an image processing card achieve" resulted in a list of requirements based on years of experience that allows the conclusion that the "impossible" must be developed. The implementation of this was only possible using the most modern, highly integrated processor technology. Today these programmable microprocessors enable the experienced developer to design the appropriate hardware exactly according to his requirements without having to become involved with the manufacture of chips. In this way it is possible to optimise the image processing hardware for the most varied inspection tasks and at the same time keep to the essentials. For example for a case inspection greater importance is attached to a high colour resolution and for a bottle inspection to a higher product frequency.
The uniqueness of the HEUFT reflexx image processing technology is therefore not the large number of software tools, similar to those available for the image processing in general use today, but the possibility to adapt the hardware to actual requirements. As a result the evaluation is extremely fast and effective. This can be compared to the graphics card in the PC sector. It is this and not the gigahertz that makes the realistic impression of many complicated computer games possible.
By using several "graphics processors", which work together via a pipeline structure and are supported by large-scale main memories, a simultaneous processing of several product shots as well as the simultaneous examination by means of different algorithms is possible. Ever-growing libraries with hardware and software tools e.g. in order to suppress knurling marks or mould seams, help to further reduce the false rejection rate. It is only possible with this combination of in-house developed hardware and software to provide the customer with systems which on the one hand take problems, that is the requirements of the market, into consideration and on the other hand yield high performance.
The success of this inspection quality combined with a greatly reduced false rejection rate cannot be acquired with mega pixels and gigahertz processors alone. It is the know-how regarding the complete process chain which makes the HEUFT reflexx image processing technology a market leader in the inspection sector.