When to choose a trilinear line scan color camera

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When you’re building a machine vision system that requires the performance and flexibility of color line scan technology, there are two different camera types you can consider: a trilinear or a prism camera. This blog explains in what situations a trilinear camera is the best choice.

Trilinear line scan camera technology

Trilinear technology uses three separate imaging lines to capture RGB images. In the past, three distinct linear sensors were mounted as close together as possible, but today most newer cameras feature a single sensor with three closely-spaced lines of pixels. Each line is equipped with polymer color filters over its pixels to capture one of the three primary colors (R, G, or B). By synchronizing the camera with the movement of the target, the images captured as each line passes over the same point on the target can be combined to provide RGB values for each pixel in the target line.

When is a trilinear camera the best option for your machine vision application?

  • When the price of the camera is an important decision factor: Especially now that most trilinear cameras are built around a single, multi-line sensor, trilinear cameras offer a less expensive option than prism cameras. In addition to the lower camera cost, trilinear cameras also offer savings over the recommended lenses needed for prism cameras. Together, this can result in savings of 50% over a comparable prism camera. Be advised, however, that several factors such as the need to use higher intensity lighting and the more rapid degradation of polymer filters vs. prism filters, may negate many of these cost savings over the lifetime of the system.
  • When your application requires high-speed imaging: Trilinear cameras are known for their ability to deliver accurate (non-interpolated) RGB image data at fast line rates. The latest 4K models (4096 pixels per line) can operate as fast as 50 kHz to 70 kHz (50 to 70 thousand lines per second). Comparable prism cameras have traditionally not been able to match those line rates, though new prism cameras are now available with almost the same speed as the fastest trilinear camera.
  • When you can guarantee a roughly perpendicular alignment: When trilinear cameras are tilted relative to the target, the distance from the target to each of the three sensor lines becomes different, slightly changing the length covered by each line on the target. If the tilt is small, compensation algorithms in the camera can make adjustments. But for larger angles, the offset can create color fringes (“halos”) or other artifacts in the image. A trilinear camera will perform best when the angle to the target is close to perpendicular and will not require frequent changes.

Need help selecting the right color camera for your application? 
Download our Tech Guide: Color Imaging
, and walk through the steps of selecting the right color imaging camera for your application.

  • When working with a flat surface with minimal undulations: Because the three lines needed to collect full RGB information must be captured at slightly different points in time, ripples or other surface vibrations can cause the target to be closer or farther away when each line is captured. This can create pixel offsets and “halos” as described above. Similarly,  discrete objects that might wobble or roll when moving on a conveyor can cause inconsistency between the three lines captured. For best results, trilinear cameras should be used when the target is flat and any fluctuations are small.
  • When your system requires a resolution above 4k: The highest resolution for a prism line scan camera today is 4K. If your line scan system calls for an 8K or 16K line resolution, trilinear will be the only option.
  • When your system requires a small-sized and lightweight camera with low power consumption: Trilinear cameras are generally smaller than prism cameras which must accommodate the prism and multiple imagers. On top of that, because a prism camera is bigger and has separate control of 3 imagers, it is naturally heavier and requires more power to operate. 

Application examples

Here are a few applications where Sweep Series trilinear cameras are especially suitable:

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Inspection of color print materials on web
presses including magazines, brochures,
flyers, packaging, etc. 

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High-speed inspection of roll-based products
including colored films, plastics, textiles,
roofing materials, and more .

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Sorting of lumber by color and grain pattern,
color matching on laminates and other flooring products.  

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Color uniformity on wafer surfaces, patterned
wafer inspection, and other wafer/IC defect inspections.

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Sorting of small parts by color, checking of
resistor values, inspection of wiring and
component placement on printed circuit boards.

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Inspection of tiles looking at color uniformity
and flaws in the glace.

Trilinear or prism camera?

Need help selecting the right color imaging camera for your application? Read our Tech Guide: Color Imaging, and walk through several steps to select the right color imaging camera for your application.

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