Photometric stereo image (left) can be combined with a texture image (right) to read different pharmaceutical packaging codes

full colour segmented ring light, the latter also being ideal for ultra-resolution colour imaging, another CI technique of growing interest. It works by taking three separate 8-bit red, green and blue images with a monochrome camera and then merging them to output a high-resolution 24-bit composite colour image. Composite colour images are much sharper than those produced by a single image capture with a Bayer or mosaic colour camera, as every pixel on the sensor is used to form the image – there is no interpolation of pixels as would be the case when using a Bayer filter. ‘Te images are of similar quality to

those from three-chip cameras without the expense, special prism or lens limitations, and are at much higher resolutions than that of available three-chip cameras,’ remarked Landman. ‘When zooming in on the composite image, edges appear much sharper, contrast and colour may be improved and noise is reduced compared to an equivalent Bayer colour image. In addition, other artefacts such as red and green aliasing are eliminated.’ While this CI technique has been around for a while, it has not been commonly used in factory automation, according to Landman.

‘Te need for illumination to be integrated within the machine vision system, rather than be a separate function, is so important’

Now, however, thanks to fast cameras and data interfaces, and higher computational power being more widely available, it is becoming more practical to use ultra- resolution colour imaging in online industrial applications. ‘It is now possible to do this at high frame

rates,’ Landman said. ‘We are strobing our red, green and blue full colour ring light sequentially at 180fps – 60fps red, 60fps green and 60fps blue – merging those together, and outputting the 24-bit colour image at 60fps, using a 12-megapixel CXP4 monochrome camera with a CXP4 frame grabber.’ Together with other CI techniques

A segmented full-colour ring light from CCS, suitable for both photometric stereo and ultra-resolution colour imaging | @imveurope

such as extended depth of field and HDR, photometric stereo and ultra-resolution colour imaging are already used in the automotive, pharmaceutical, food, healthcare, packaging, electronics and wood industries. Tey are being used for applications as varied as identifying small surface defects, revealing overlaid text and barcode information, reading braille characters, inspecting tyres, improving colour fidelity, highlighting pinholes in food packaging, and imaging objects of different heights in the same field of view. In addition to ring lights, another key

component developed by CSS for CI is its four-channel programmable lighting

controller, the Light Sequencing Switch (LSS), responsible for managing the necessary image capturing sequences in CI. ‘Te flashing of the light needs to be synchronised with the exposure of the camera, and coordinated with the part moving under the camera while shifting the focus of the lens,’ explained Landman. ‘A tracking algorithm is therefore used to track the object through each frame as it passes under the camera; you can then shift the pixels to merge the images together.’

Further integration needed Despite the greater uptake of CI in machine vision, Landman believes a higher level of integration between the components involved must first be achieved before it can fully take off in industry. ‘Te need for illumination to be integrated

within the machine vision system, rather than be a separate function, is so important,’ he said. ‘Te way I see it playing out over time is that the multiple components required to perform CI will become more tightly integrated within the camera. Tat’s the direction I hope this will go in the future. It will require camera, lighting and lens manufacturers to all work together in order to provide this tight integration and improved imaging capability.’ Landman is not alone in highlighting the

need to bring the separate components of CI together in one solution. John Trailkill, co-founder and CEO of

Advanced Illumination – another lighting firm making big moves into CI – also expressed a need for more mature solutions should CI wish to see greater uptake in industry. ‘We have every indication that this is a very

powerful imaging technology. However, it’s still fairly new,’ he said. ‘CI has to be easy to




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