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3CCD cameras for industrial applications Presentation at Vision 2005 Industrial Vision Days Stuttgart Messe JAI Camera Solutions Gunnar Jonson

Scope of presentation u The history of 3CCD cameras u The principle of 3CCD cameras u Color vs Monochrome imaging in Machine Vision u Other color imaging technologies u Industrial 3CCD application areas

The history of 3CCD cameras Tube based cameras u In the beginning of video cameras, TV broadcasting was the driving force behind camera development. u Color cameras were introduced in the mid fifties, and were based on three image tubes (CCDs weren’t even invented yet), coupled to a set of mirrors and filters. u Later, a glass prism block was used to separete the RGB components.

The history of 3CCD cameras CCD based cameras u As CCD image sensors became a reality in the seventies, broadcast cameras were among the first to adopt these into prism based assemblies. u Over time, 3CCD cameras have also made their way into non- broadcast applications, primarily for use with microscopes. u Machine vision has been relatively slow to adopt 3CCD cameras, primarily for cost reasons.

The principle of 3CCD cameras u At the heart of the 3CCD cameras is the prism block. u It is built up of three glass wedges, with dichroic hard coatings separating the three color bands red, green and blue (RGB) Camera Lens IR-cut filter High-pass coating Low-pass coating

The principle of 3CCD cameras u The dichroic coatings on the prism provide excellent separation between the color bands. u Unlike mosaic (single chip) designs, the dichroic coatings do not degrade over time. Wavelength (nm ) Relative transmission IR stop B G R

The principle of 3CCD cameras u The same basic technology can also be applied to line scan cameras. u The precision of the alignment of the image sensors is in this case extremely critical. Red sensor Blue sensor Green sensor Lens IR-cut filter

Color vs. Monochrome u The majority of machine vision applications are solved using monochrome cameras. l The main reason is to conserve costs and processing power u Color is typically used in the Food. Pharmaceutical and Printing industry. u Where color information results in a more precise and robust solution, color cameras are also chosen.

Other color imaging technologies Bayer mosaic u This is the most common way of creating color images from an image sensor today. u In digital still cameras it is the dominant method. u Requires interpolation algorithm to ”de-mosaic” the image. Drawback: l Can never reproduce a true color image, as colors are interpolated. l Can result in edge artifacts in the transition from bright to dark. Advantage: l The cost is very reasonable and image sensors are available from several manufacturers u Patented in 1976, was invented at Eastman Kodak by Bryce E. Bayer. Illustrations courtesy of: Earthbound, Kodak

Other color imaging techologies Vertical layers u This techology mimics the way color is captured in photograpic film. u Designed for use in digital still cameras. Drawback l The charge storage capacity for each color is relatively small, which limits the dynamic range in each color Advatage l No interpolation required. The image is generated as a complete RGB image. u Patented by Foveon Illustrations courtesy of: Foveon

Other color imaging techologies Filter wheel u By taking 3 subsequent images through red, green and blue filters respectively, it is possible to create images with the same color fidelity as 3CCD cameras. u Not practical for use in machine vision applications. u Suitable for microscopy and similar. Drawback l The object must not move between the 3 captures. Advantage l No prism artifacts that need to be corrected for. Lens Filter wheel Image sensor

Industrial 3CCD application areas u 3CCD cameras have numerous advantages over other solutions, but as it is a more costly technology, it will be limited to use where the alternative color technologies are not suitable. u Food processing u Textiles, plastics u Lumber / wood u Pharmaceuticals u Print quality inspection u Ceramic tile inspection u Flat panel display inspection

Industrial 3CCD application areas Food processing u Inspecting fruit and vegetables for blemishes. u Quite often the blemish is hard to detect as it close to the color shade of the object itself. u 3CCD cameras are are preferrable to single-chip cameras, as they provide better resolution and color rendition. u Special transport mechanisms and ”unwrap” software is also required to process the whole surface. Picture courtesy of Vision Machines Inc / Photonics Spectra

Industrial 3CCD application areas Food processing u For food processing, 3CCD line scan cameras provide a unique solution. u This is particularly true when sorting bulk food, such as nuts, beans and similar. u 3CCD line scan cameras can be used to view the object as they fly off the end of a conveyor belt. u Using two cameras, the objects can be viewed both from top and bottom.

Industrial 3CCD application areas Print quality inspection u The objective is to provide a consistent quality with regards to color, defects registration and sometimes content (text and codes). u For high-end applications 3CCD cameras are preferred, as they provide the best color rendition. u Very often strobe lights are used to freeze the frame effectively.

Industrial 3CCD application areas Lumber / Wood u Often involves very fine variation in color shades u Inspection is instrumental for grading and cutting. u 3CCD line scan cameras are well suited for these types of applications. u Improves yields and makes better use of natural resources. Picture courtesy of Americal Walnut Company

Conclusion u 3CCD cameras have made the move into industrial machine vision. u No longer confined to broadcast and scientific / medical use. u 3CCD cameras are superior to single-chip cameras with regards to color rendition and resolution. u Modern 3CCD cameras for industrial use provide all the functionality (trigger, progressive scan, etc) and interfacing required by the applications. u Due to the higher cost of 3CCD cameras over single-chip cameras, they are mostly reserved for the more demanding applications.

Thank you for your attention! Further information in Hall 04 – Stand 620 or at

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