Knowledge · Cameras
Line scan vs area scan
The decision starts with motion and the smallest relevant feature. Define inspection width, required resolution in both axes and maximum speed before comparing sensors or interfaces.
Decision frame
Two motion models, two sensor geometries
Area scan captures a complete 2D image per trigger. Line scan builds an image line by line while the material or camera moves. It can create a practically unlimited image length in the direction of travel; cross-web coverage remains limited by sensor width, optics, working distance and installation geometry.
Continuous web or belt
Film, textile, paper, steel strip and conveyor surfaces keep moving. Line scan uses pixels across the inspection width and builds length in the direction of travel. This can avoid image tiling or an impractically large area-scan sensor.
Typical fit: line-scan camera, lens for the required scan width, uniform line lighting and an encoder when speed varies.
Discrete field of view
A stopped or predictably presented part is often simpler with area scan. A moving part can also be captured with multiple triggers when product spacing, field of view and data volume remain manageable.
Typical fit: area-scan camera, suitable lens, trigger and short exposure or light pulse per frame.
Synchronisation
Resolution and encoder belong in the same calculation
First calculate object-space pixel size across the width from field of view and sensor pixels. Then define the required sampling distance along travel. Required line rate equals transport speed divided by that sampling distance. Check that exposure time, camera interface and processing retain sufficient margin at maximum speed.
- Without encoder: a fixed line rate assumes constant speed. Acceleration and belt slip distort the image in the direction of travel.
- With encoder: a line trigger ties sampling to measured travel. Encoder resolution, mounting position and mechanical slip determine actual accuracy.
- Area scan alternative: one or more triggered frames are often simpler when the product fits the field of view and overlap, timing and motion blur are controlled.
See also triggering and timing once geometry is fixed.
Technical boundaries
Compare the complete acquisition chain
| Situation | Line scan | Area scan |
|---|---|---|
| Long image in direction of travel | Strong fit; image length follows from line count | Multiple frames or tiling required |
| Stopped, compact part | Requires added motion and synchronisation | Complete image per trigger |
| Resolution across a large inspection width | Pixels concentrated across width; line rate defines the second axis | Larger sensor, more cameras or tiling |
| Lighting and focus | Check uniformity across scan width and focus line | Check uniformity and focus across the full field of view |
| Data volume and buffering | Depends on line rate and image length | Depends on frame size and trigger frequency |
Have the geometry calculated
For selection, also include available space, working distance, product guidance, permitted motion blur, maximum image length and required storage.