Basic Knowledge of Vision Sensors

Basic Terms You Should Know

Glossary

Term	Description Term	Term	Description Term
Resolution	Describes the ability of a system to distinguish, detect, and/or record physical details by electromagnetic means. Normally, described by number of pixels in X and Y.	Effective pixels	Pixels actually used effectively. Normally, edge part of image sensor chip would have noise or image on those parts would be distorted so pixels at center area will be used actually.
Focal length	The distance between center of the lens and the point that collimated light beams are brought to focus. The wider angle lens have the shorter focal length. Described as f25mm for example.	Depth of field (DOF)	Distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Reducing the aperture size increases the depth of field.
Field curvature aberrations	The image points near the optical axis will be in perfect focus on the flat image sensor, but rays off axis will come into focus before the image sensor, this creates image distortion as curvature aberrations.	Angle of view (AOV)	Describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view. The smaller AOV, the smaller distortion.
Working distance (WD)	The distance from the front of the lens to the target object.	Field of view (FOV)	The area of the inspection captured on the camera's image sensor. The size of the field of view and the size of the camera's image sensor directly affect the image resolution.
Optical magnification	The ratio of size of the FOV and the size of the image formed on the image sensor.	Binalization	Binalization is distinguishing colors to black or white separate by a threshold. It makes data size very small though, resolution of the image will be reduced.
Shutter time	The period that the shutter is open. It will be defined depending on the moving speed of the target object and brightness of the lighting. When the moving speed of the object is fast, shutter time should be short. In that case, lighting should be bright enough to capture bright image in that short period.	Gray scale image processing	Image processing using multiple gradation gray scaled data. It can keep image resolution high though, processing time will be long because data size will be big.
Progressive scan	A way of displaying images in which all the lines of each frame are drawn in sequence. This is in contrast to interlaced scan. All the lines to be processed for one frame so the data size will be bigger and taking time for processing.	Sub pixel processing	A 10th of the pixel. Calculate brightness or color of each sub pixel from brightness or color of neighbor pixels. This enables very precise measurement.
Interlaced scan	A way of displaying images used in traditional analog television systems where only the odd lines, then the even lines of each frame are drawn alternately, so that only half the number of actual image frames are used to produce video.	Pattern searching	Searching image shape close to the stored image as search model in the captured image. It provides correlation level, how much the image is resemblant to the search model, and coordinate of the image.
Polarizing filter	The filter that let only one direction wave of light go through. For machine vision purpose, mainly it is used to manage reflection so that the camera can capture clear image.	Extension tube (Extension ring)	Ring or tube shaped spacer put between lens and camera to adjust focal length used especially when shorten the focal length.

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