Machine Vision Glossary
Short definitions of terms commonly used in machine vision and camera-based quality control.
We have collected the terms that come up most often in camera-based quality control projects, grouped by topic. Each term is defined briefly; follow the link to the related article or page for details.
Basics
- Machine vision
- Analysing camera images with software to make decisions about a product. In manufacturing it is used for defect detection, measurement, reading and robot guidance.Learn more
- Visual quality control
- Quality control based on the appearance of a product. It can be done by hand or automatically with camera systems.Learn more
- Camera inspection system
- A system of camera, lighting, software and rejector that images the product, evaluates it, removes defective products and records the decision.Learn more
- Automated optical inspection (AOI)
- Automatic camera inspection of component presence, position and solder joints in electronics assembly.Learn more
- OK / NOK
- Marking a product as accepted (OK) or rejected (NOK) after inspection. A NOK decision is stored with the reject reason.
- False reject
- A good product that the system flags as defective and removes. The false reject rate is one of the measures that determines production loss.
- Escape
- A defective product that the system accepts as good. It is the most critical measure for quality, and acceptance limits are set around it.
- Reference sample
- Good and defective product samples of known status used to define inspection criteria and validate the system.
- Product profile
- The set of inspection settings and criteria defined for one product. The matching profile is selected at product changeover.
- Region of interest (ROI)
- The area of the image where inspection takes place. Examining only the necessary area improves both speed and reliability.
- 100% inspection
- Inspecting every product produced instead of sampling. Camera inspection systems can carry out 100% inspection at line speed.
Camera and lens
- Industrial camera
- A camera built for production environments that captures images on a trigger signal, with fixed settings and in a repeatable way.Learn more
- Area scan camera
- A camera that captures the image in one shot as a rectangular frame. Widely used for discrete products.Learn more
- Line scan camera
- A camera with a single row of pixels that builds the image line by line as the product moves. Used for continuous materials such as fabric, film and sheet.Learn more
- Global shutter
- A shutter type in which all pixels on the sensor are exposed at the same time. It prevents distortion of moving products.Learn more
- Rolling shutter
- A shutter type in which sensor rows are exposed one after another. Fast-moving products can appear tilted or distorted.
- Resolution
- The number of pixels on the sensor. The required resolution is calculated from the field of view and the size of the smallest defect.Learn more
- Monochrome camera
- A camera that captures greyscale images without colour information. At the same resolution it is sharper and more sensitive to light.
- Exposure time
- The time during which the sensor collects light. Short exposure prevents motion blur on moving products but needs stronger light.
- Motion blur
- Blur caused by the product moving during exposure. It is usually kept below one pixel.
- Frame rate
- The number of images a camera can capture per second. It is chosen for the number of products passing on the line.
- Triggering
- Capturing the image the moment the product arrives in front of the camera, on a sensor or PLC signal.
- Encoder
- A sensor that measures the movement of a conveyor or material. With line scan cameras it matches the image to material speed.
- GigE Vision
- An industrial camera interface standard over Ethernet. It supports long cables and power over the cable with PoE.
- USB3 Vision
- An industrial camera interface standard over USB 3. It offers a high data rate with short cable lengths.
- Focal length
- The value that sets a lens’s angle of view. It is chosen from the working distance and the required field of view.
- Field of view (FOV)
- The size of the area the camera covers in the image.
- Working distance
- The distance between the front of the lens and the product.
- Depth of field
- The range of distances over which the image stays sharp. It increases as the aperture is closed, but less light reaches the sensor.
- Telecentric lens
- A lens that keeps the product’s size in the image constant even when its distance changes. Preferred for precise measurement.Learn more
- 3D camera
- A camera that captures height information of a surface. It works with laser triangulation, structured light or stereo methods.
- Laser triangulation
- A 3D method that measures height by imaging a laser line projected on the surface from an angle.
Lighting
- Bright field
- A lighting geometry in which light reflects off the surface into the camera. Flat surfaces look bright; defects that scatter light look dark.Learn more
- Dark field
- A lighting geometry in which light hits the surface at a very shallow angle. Flat surfaces look dark; scratches and embossing look bright.Learn more
- Ring light
- A light placed around the camera that illuminates the surface directly.
- Dome light
- Lighting that spreads light from all directions for a shadow-free, glare-free image. Used on glossy and curved surfaces.Learn more
- Coaxial light
- Lighting that shines along the camera axis through a half mirror. Used on flat, glossy surfaces.Learn more
- Backlight
- Lighting from behind the product that creates a sharp silhouette. Used for contours, dimensions and checking inside transparent products.
- Strobe lighting
- Light that is on only briefly while the image is captured. It freezes moving products and can be driven brighter than continuous light.
- Polarising filter
- A filter fitted to the light and lens to reduce reflections on glossy surfaces.
Software and AI
- Rule-based inspection
- Machine vision using fixed thresholds, measurements and rules. Used for clearly defined tasks such as measurement, counting and presence checks.Learn more
- Deep learning
- An AI method that learns from example images. Used to detect textures, patterns and defects that vary in shape.Learn more
- Anomaly detection
- Training a model on images of good products only and flagging anything that deviates from them. Suited to rare defects.Learn more
- Classification
- Assigning an image or defect to one of several predefined classes, for example sorting by defect type.
- Segmentation
- Assigning every pixel of an image to a class. This is how the location and size of a defect are determined.
- Data labelling
- Marking the location and type of defects in training images. Model accuracy depends on the accuracy of the labels.
- OCR (optical character recognition)
- Reading text and numbers in an image. Used to check date codes, lot numbers and serial numbers.Learn more
- OCV (optical character verification)
- Verifying that the text read matches the expected content and checking print quality.Learn more
- DataMatrix and 2D codes
- Codes that store data in a two-dimensional square pattern. Used on pharmaceutical packs to carry serial numbers.Learn more
- Calibration
- Mapping image pixels to real-world dimensions and positions. Needed for measurement and robot guidance.
Quality and production
- Rejector
- The device that removes defective products from the line. It can work as an air jet, a pusher arm or a diverter gate.
- PLC
- The programmable controller that runs a production line. A camera system can receive its trigger from the PLC and send the result and reject command back.
- Traceability
- Being able to trace back from records when, on which line and with what result a product was inspected.
- Non-destructive testing
- The general name for inspection methods that do not damage the product. Visual testing, X-ray, ultrasonic and penetrant testing are among them.Learn more
- 4-point system
- A fabric grading method in which defects get 1 to 4 points by size and the total is calculated against the inspected area.Learn more
- Poka-yoke
- An error-proofing method that prevents a defect from occurring or moving to the next step. Camera inspection can act as poka-yoke in assembly.Learn more
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