Vision Basics - Resolution A pixel can be thought of as a single cell in a matrix that the camera overlays on the field of view (FOV). For a black-and-white camera, the value that is placed in a cell (pixel) is a shade of grey that represents the intensity of the light reflected from the corresponding area in the field of view. Note that, in a line scan camera, one dimension of this matrix is retrieved by a row of sensors, each of which returns a pixel. The difference between matrix cameras and line scan is in the other dimension of the matrix. A line scan camera takes repeated images of a mov- ing target to build the second dimension.
The first dimension's resolution is just like a matrix camera, and dependent on the number of pixels that the camera returns. The second dimen- sion's resolution is dependent on how often an image is acquired relative to the amount of movement of the target, typically moving on a conveyor belt. Resolution The camera representation of our hypothetical 22 x 16 camera shows very poor resolution due to the low density of pixels. In addition to the number of pixels in the camera array, the lens focal length combined with the distance of an object from the camera has the greatest effect on the final resolution of whatever you are viewing.
The following figures show the relationship between focal length and viewing distance. In general, the best resolution comes when the object of interest fills as much of the field of view as possible while still being in focus. An important concept that is illustrated by these figures is the relationship between a pixel and the physical size of an object. A pixel always has a relative relationship to the size of an object. It has an absolute relationship only when you fix your viewing distance and focal length of the lens, and then calibrate the vision system.
The camera calibration process (Stan- dalone Camera Calibration on page 320) establishes an absolute relationship between a pixel and the actual dimensions of the field of view. ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 304