Image measuring instrument is mostly non contactmeasurement of optical, belonging to the two dimensional measurement; three coordinates are contact measurement, and belongs to the field of 3Dmeasurement.

Image measuring instrument by using the hardware itself(CCD, eyepiece, objective data line) which can capture the image through the data to the data acquisitioncomputer card, followed by the software on the computer display imaging, by the operator using the mouse on the computer for rapid measurement. Therefore the measured plane is more convenient; and the threecoordinates are obtained by the probe head and the workpiece to achieve the measurement of contact.

They each have advantages and disadvantages. Non contact measurement using image measuring instrument,the use of cold light source system, can avoid the easy deformation of the workpiece is the error because of the heat and the deformation produced in the measurement.Detection of rubber, soft plastic workpiece, and the workpiece can be arbitrarily placed. The three coordinateis three-dimensional workpiece can be measured easily.High precision measurement of geometric surface,complex shape parts and mechanical parts, free surface,may select the contact or non-contact probe scanning.

In addition some high-end image measuring instrument(like we usually say 2.5D, 3D optical image measuring instrument), can add the probe, the Z axis height measurement purpose. It is a supplement to the optical image of two-dimensional measurement.