Line Scan vs Area Scan Cameras for Inspection

Continuous materials and discrete parts need different cameras. Line scan vs area scan, how to choose, and what to prepare, with IntScan Pro and IntSight.

Should machine vision inspection use a line-scan camera or an area-scan camera?

Line scan is the starting point for materials that run without a break, such as paper, film, metal and textiles; area scan is the starting point for discrete parts such as coils and FPCs. Most cases are settled by whether the product comes in separate pieces, how small the defect is relative to the width, and whether the product can stop for imaging. If it is unclear, image samples and decide.

How the two cameras capture images

An area-scan camera captures a whole area at once, like an ordinary camera. The moment a part comes under the camera, it receives a trigger and takes one image, and the decision is made from that one image.

A line-scan camera has a sensor that captures only one line, and it keeps capturing lines and stitching them together as the material passes. The material has to move for an image to form, so imaging is usually synchronized to the movement with an encoder. That is why endless material can be viewed without a break.

Side by side

  • Item: Best suited to; Line scan: Materials running continuously, such as paper, film, metal and textiles; Area scan: Parts arriving one by one, such as coils and FPCs
  • Item: Imaging; Line scan: One line at a time, stitched together; Area scan: One whole image at once
  • Item: Imaging signal; Line scan: Trigger and encoder, following the movement; Area scan: PLC trigger, following the part's position
  • Item: Values that set resolution; Line scan: Width, defect size to find, line speed; Area scan: Field of view, defect size to find
  • Item: Lighting; Line scan: Long, along the imaging line; Area scan: Matched to the part's shape and the defect
  • Item: INTELLIZ product; Line scan: IntScan Pro; Area scan: IntSight

IntScan Pro and IntSight are two different products. Either one applies an inspection package (.izpkg) built in IntLearn Pro.

Three questions for choosing

  • Does the product come in separate pieces? If it unwinds from a roll and keeps running, line scan; if it arrives one piece at a time, start with area scan.
  • How small is the defect relative to the width? Finding small defects across a wide width is hard to fit into one image, so line scan gains the advantage.
  • Can the product stop for imaging? If it can stop or be positioned, area scan is simpler. Moving discrete parts can also be imaged by area scan with a short exposure or strobe lighting. A continuous process that cannot stop points to line scan.

Borderline cases

Even with discrete parts, if they are long, run on a conveyor without stopping, or have a cylindrical surface that must be rotated to inspect, it is hard to say right away which is better. Parts with several faces to inspect also call for working out the number and placement of cameras. In these cases, do not decide by discussion; image samples and decide.

In the Optics Lab, choose the material, the defect and the line conditions to see whether it can be inspected with IntScan Pro line scan or needs a sample demonstration, and you can also compare part lighting for IntSight area scan.

Values to prepare before a consultation

For line scan there are three: width, line speed and the smallest defect size to find. These values determine the number of cameras, the lines per second and the pixel size. The calculation is in the paper line-scan guide.

Illustrative example: if you capture one line every 0.1 mm in the running direction, a line speed of 600 m/min (10,000 mm per second) requires 100,000 lines per second.

IntScan Pro inspects with 1 to 5 cameras in parallel. If the width is large, the number of cameras is the first thing to look at together.

For area scan there are four: the field of view (the range to fit in one image), the smallest defect size to find, the time available to image and decide on one part, and the number of faces to inspect.

Illustrative example: with a horizontal field of view of 100 mm and 5,000 horizontal pixels, one pixel is 0.02 mm. A defect that covers only one or two pixels is easy to miss.

Limits and cautions

The numbers above are examples showing the calculation, not product specifications. The actual configuration is given in a quote after samples and site conditions are checked. Whether a defect shows up well often depends on lighting and angle more than on the camera type.