Two-chip cameras are a peculiarity on the market and are offered only by few manufacturers. They are capable to capture the same object with two sensors. The advantage over two individual cameras is that the images are aligned without any offset sharp to the pixel. The machine vision user therefore receives additional image information from the second sensor for each pixel, which could not be obtained using only one camera.
Functional principle of the two-chip colour camera
The functional principle is similar to the known technology of three-chip cameras: in this case, the incident light is deflected by means of a prism block and elimination filter foils to two different sensors precise to the sub-pixel.
- Two monochrome sensors: can be operated with different exposure times. This results in images with a clearly higher dynamic range without overexposure or underexposure. This is a HDR (high dynamic range) camera. Extremely fast two-image exposure sequences are conceivable, too. Within micro-seconds, two successive images can be captured, which would not be possible using only one sensor.
- Colour sensor and NIR sensor: in addition to a colour image, the user gets an infrared image in which the colours of the objects are not visible, but other features are well depicted.
Fields of application and examples
Example: food industry
The colour information can be used for a common visual inspection, whereas the infrared radiation penetrates deeper into the material and makes defects visible there. Rotten spots and damage, for instance on fruits, can be better examined in the IR spectrum.
Colour image Avocado
Infrared image Avocado
Example: safety technology
Safety features are detected in IR light, while a conventional image in the visible range of light is additionally available. Whereas the colour information mostly vanishes when illuminated with infrared light, special IR-active dyes but also black imprints remain visible. Credit card numbers, for instance, can be correctly identified on coloured cards in this way.