What is a line scan camera?

What a line scan camera is

A line scan camera is an industrial camera whose sensor is essentially a single row of pixels, sometimes a few rows for multi-line or TDI designs, rather than a full rectangular matrix. Instead of freezing a complete 2D frame in one exposure, it captures one thin line of the scene at a time. As the product moves under (or past) the camera, successive lines are stacked in software or hardware into a continuous two-dimensional image.

That architecture is why line scan dominates continuous material inspection. Film, metal strip, paper, textiles, printed webs, and high-speed conveyors rarely stop for a photograph. An area scan camera would either blur, miss sections, or require an impractically wide field of view at microscopic resolution. A line scan camera matches motion: the material supplies the second image axis.

In catalogues you may see line camera, linescan, web inspection camera, or linear sensor camera. In Sedeco’s taxonomy they sit under Cameras, alongside area scan, smart and 3D families. The buying decision is less about brand and more about whether your process is continuous and motion-synced.

How a line scan camera works

Think of four linked decisions: motion → line exposure → optics & light → interface & reconstruction.

1. Motion supplies the second axis

The product moves past a fixed camera (or a camera scans across a stationary object, less common in web lines). Each line corresponds to a thin cross-section of the material. If lines are taken at the wrong rate relative to speed, the reconstructed image stretches or compresses along the travel direction. That is why motion sync, typically an encoder on a roller or conveyor, is central to line scan, not optional.

2. Each line is a short exposure

Line rate is how many lines per second the camera can capture (for example tens of thousands of lines/s on modern sensors). Exposure time per line is short. Bright, uniform illumination across the scan line is therefore critical, often a high-power line light or strobe-capable bar matched to the optical path. Without enough light, you raise gain and add noise, or you lower line rate and lose spatial sampling at speed.

3. Optics map web width onto the line

Across-web resolution comes from how many pixels span the material width. A 4k, 8k or 16k line sensor is common language for “how many samples across the web.” Lens choice, working distance and magnification decide micrometers per pixel. Camera choice without optics is incomplete, see our lenses overview when you size field of view across a strip.

4. The interface streams lines continuously

Line scan often pushes high sustained bandwidth. Camera Link, CoaXPress and high-performance GigE / 10GigE variants appear frequently. Software or a frame grabber assembles lines into images (or processes them as a continuous stream). GenICam-style control still applies on many modern line scan cameras for exposure, encoder modes and ROI along the line.

Line scan vs area scan, smart, and 3D

Teams often ask for “an industrial camera” when they need a family decision. Use this comparison before you open a datasheet.

Line scan vs area scan: if the product is a discrete object that stops or moves slowly in a window, start with our area scan guide. If material streams continuously and you need fine defects along meters of product, or you need thousands of pixels across a wide web, line scan is usually the tool. Many factories use both: area scan on assembly cells, line scan on webs.

Line scan vs smart camera: web inspection is typically PC-based or vision-controller based because of bandwidth, encoder logic and continuous algorithms. Architecture still matters, see smart camera vs PC-based vision, but for classic line scan webs, expect a PC or dedicated vision PC path.

Line scan vs 3D: line scan answers “what does the surface look like along the travel?” 3D answers “what is the height or shape?” Some lines combine a 2D line scan for print/coating with a separate 3D profiler for thickness or warp.

Where line scan cameras are used

If you are buying Computer Vision for continuous product, these patterns cover most successful line-scan projects:

• Web and film inspection, Coating streaks, gels, holes, contamination and gauge marks on plastic film, foil and paper.
• Print and converting, Register, missing print, color bars, splice detection and barcode/OCR on continuous packaging material.
• Metal strip and steel, Surface scratches, roll marks, edge defects and scale on continuous strip at high line speeds.
• Textiles and nonwovens, Holes, thick spots, contamination and weave defects across wide webs.
• High-speed conveyors, Sorting or surface checks where parts never pause and a single area-scan FOV cannot cover width at the required resolution.
• Flat panel and glass (selected lines), Long, continuous scanning of large sheets where stitching many area frames is less practical.

The common thread is continuous motion plus a need for across-web resolution that would force an area scan camera into either huge megapixel counts, multiple cameras, or unacceptable blur.

Specs that actually matter when you buy

Datasheets for line scan are dense. prioritize the list below. “8k” alone rarely decides success.

Pixels across the line (resolution)

Resolution here means samples across the web (2k, 4k, 8k, 16k and similar). Rough rule: plan several pixels across the smallest critical defect so detection stays stable when contrast varies. Combine pixel count with optical magnification to get µm/pixel across the material. Higher pixel counts raise optics cost, light demand and bandwidth.

Line rate

Line rate must keep up with material speed at the spatial sampling you need along the travel direction. If the web moves faster than your lines can sample, you under-sample defects along the machine direction. Marketing “max line rate” is often stated at reduced bit depth or ROI, verify for your pixel format and interface.

Encoder sync and trigger modes

Confirm the camera (or grabber) supports the encoder interface and frequency you need. Free-run line scan without encoder only works when speed is perfectly constant, rare on real lines. Quadrature encoders, gear ratios and electronic gearing are part of the design, not afterthoughts.

Mono vs color vs multi-spectral

Mono line scan is the workhorse for surface defects and geometry cues. Color line scan matters when print color or material tint defines the defect. Some applications use dual-line or multi-spectrum setups; treat those as application engineering, not catalogue browsing.

Interface and bandwidth

Sustained line streams need a clear path to the PC or vision controller. Camera Link and CoaXPress remain common for high line rates; GigE / 10GigE variants serve many mid-range webs. Cable plant, frame grabber and NIC tuning matter as much as the camera body.

Lighting dependency

Line scan fails quietly with poor light: uneven intensity across the web, specular hotspots, or insufficient photons per line. Budget time for line-light geometry trials, start from our lighting page when you design the station.

Building a working line-scan setup

A reliable station is a system, not a SKU:

1. Camera, pixels across, line rate, interface matched to speed and width.
2. Lens, magnification and resolution class for µm/pixel across the web.
3. Line lighting, uniform intensity, often high power; geometry matched to surface finish.
4. Mechanics, rigid mount, vibration isolation, precise alignment perpendicular to travel.
5. Encoder & sync, calibrated pulses per millimeter of travel.
6. Compute & software, grabber or NIC, continuous inspection recipes, reject marking or logging.

Common first-system mistakes

• Buying “8k” without calculating µm/pixel at the actual web width.
• Ignoring encoder sync, then wondering why images look stretched.
• Under-lighting the line and compensating with gain that hides small defects in noise.
• Mounting the camera at a slight angle so the optical line is not square to travel.
• Choosing an interface that cannot sustain peak line rate for a full shift.
• Skipping sample variation, shiny, dirty and translucent webs all appear on Monday morning.

How to read a line scan product page

On Sedeco product pages for line scan families you will typically see cues such as sensor resolution (pixels across), max. line rate, mono/color, and interface. Read them as answers to the eight questions above:

• Pixels / resolution, samples across the web; combine with optics for µm/pixel.
• Max. line rate, ceiling under stated conditions; confirm for your format and interface.
• Data interface, how lines reach the PC or controller continuously.
• Mono/color, intensity vs color decisions on print or coatings.
• Encoder / trigger features, whether motion sync is native or needs grabber support.

When you evaluate “line scan camera,” that phrase can link here so you can understand the category before comparing models in the camera catalogue. Do not treat catalogue numbers as a substitute for a speed-and-resolution calculation on your web.

Worked example: line rate and sampling

Suppose you inspect a plastic film that is 1 200 mm wide. The critical defect is a 0.5 mm hole. You want at least 5 pixels across that hole across the web.

Required spatial sampling across web: 0.5 mm / 5 = 0.1 mm per pixel. Across 1 200 mm you need 1 200 / 0.1 = 12 000 pixels, so an 8k sensor alone is not enough unless you narrow the FOV, use multiple cameras, or accept fewer pixels on the defect. This is why width and defect size drive pixel count before brand preference.

Now speed: the web runs at 300 m/min = 5 m/s. If you also want 0.1 mm sampling along travel, you need a line every 0.1 mm → 5 / 0.0001 = 50 000 lines per second. That line rate must be available at your bit depth and interface, and lighting must deliver enough photons in each short exposure.

These back-of-envelope numbers explain why project teams should not start from “the highest k” in a brochure. Start from defect size, width and speed. Then confirm with real samples under real line lighting. Sedeco often runs a short feasibility pass for exactly this reason, see the feasibility checklist.

Industry snapshots

Line scan shows up differently by sector. The sensor family stays the same; lighting, encoder placement and acceptance criteria change.

Converting and flexible packaging

Coating, laminating and print inspection on continuous film. Defect maps, roll reports and splice handling dominate the software story. Color may matter for print; mono often wins for gels and holes.

Metals and steel

High line speeds, reflective surfaces and harsh environments. Lighting geometry and housing protection matter as much as pixel count. Edge and surface defects drive reject logic upstream of coiling.

Paper, pulp and textiles

Wide webs, dust, and long continuous runs. Multi-camera stitch across width is common. Maintenance access and calibration routines must be designed for operators, not only for engineers.

Logistics and high-speed sortation

When parcels or items never pause, a line-scan tunnel can build a continuous image for dimensioning cues or surface checks. Many sites still use area scan for codes; the family choice follows the task.

Machine builders and OEMs

You standardize on a line-scan family and encoder recipe across machines shipped worldwide. Long-term availability, grabber compatibility and documented optical recipes weigh as heavily as peak line rate.

Integrating with PLC, encoder, and IT

A line scan camera rarely stands alone. Typical industrial loops look like this:

• Encoder in, pulses proportional to travel drive line acquisition.
• Acquire, continuous lines under stable line light; stream to PC or vision controller.
• Decide, software finds defects, maps them to meter marks, and grades severity.
• Act, PLC marks, rejects, slows, or logs a roll report to MES.

Latency and buffering matter: continuous streams must not drop lines at peak speed. Switch quality, grabber settings and disk logging policies are part of commissioning.

If you are unsure whether processing should live on a smart device or a PC, settle architecture early, via the smart vs PC decision page, then freeze the line-scan interface.

Cost, quality, and what good enough means

Teams sometimes under-buy line lighting and mounts to save on the camera, then spend months fighting false rejects and stretched images. The inverse also happens: an expensive high-k sensor with a weak encoder path and ambient light. Image quality is a chain; the weakest link sets the false-reject rate.

Practical budgeting for a first web station often allocates meaningful spend to lighting, encoder mechanics and vibration control, not only to the camera body. A well-lit, correctly synced mid-resolution line scan routinely outperforms a higher-k camera that is starved of light or mistimed.

Define acceptance with samples: golden rolls, borderline fails, and dirty or reflective variants. If you cannot show the defect to a human under the proposed line light, software will struggle too.

Short glossary

Line rate

Lines captured per second, must match speed × desired sampling along travel.

Encoder sync

Using a motion pulse train so each line maps to a known distance of travel.

Web / strip

Continuous material moving through the process (film, paper, metal, textile).

Across-web resolution

Spatial sampling perpendicular to travel, set by pixels and optics.

TDI

Time Delay Integration, multi-line sensors that accumulate light while tracking motion.

Frame grabber

Hardware that receives high-bandwidth camera data (common with Camera Link / CXP).

Line light

Illumination shaped as a bright line matched to the sensor’s view of the web.

FAQ: line scan cameras

How this guide fits your selection

Use this guide when you are still deciding whether line scan fits your process, before you compare model options. Focus on encoder sync, line rate, web width and lighting across the scan line.

Related reading lives under Knowledge.

Next steps

You now have the category model: line scan builds a high-resolution image from successive lines on continuous material, provided motion sync, optics and line lighting are designed with the camera.

Related: Knowledge hub · Area scan guide · Feasibility checklist.