Advanced Mathematical & Computational Tools in Metrology & Testing VIII, p.p. 243-248 World Scientific, ISSN: 1793-0901, ISBN-130976-981-283-951-0, ISBN1-10 981-283-951-8, Cachan, France, Jun 2008 ROBUST LINE DETECTION FOR LINE SCALE CALIBRATION JOSÉ ANTONIO MUÑOZ-GÓMEZ Universidad de Guadalajara - CUCSUR, Av. Independencia Nacional 151 Autlán de Navarro, Jalisco, C.P. 48900 MEXICO, e-mail: jose.munoz@cucsur.udg.mx CARLOS GALVAN Centro Nacional de Metrología (CENAM), km 4,5 Carretera a los Cues Mpio El Marques,Querétaro C.P. 76241, MEXICO, e-mail:cgalvan@cenam.mx A novel method for detection of lines in a digital image used in line scale calibration process is described. The line images are recorded by a moving microscope and a CCD camera. This method is based on the center of the line instead of the edges of the line. Line detection is one of the most important problems in the line scale calibration. This method uses a Gabor filter for each row in the digital image. Likewise, based on robust statistics, some outlier points due to imperfections in the mark on the scale are ignored. Keywords: Line detection, scale calibration, Gabor filter. 1. Introduction Historically, measurement of graduated lines scales is one of the most important tasks in the traceability chain for the measurement of the unit of length. Before 1961, the length of a meter was defined as the distance between two graduation lines on a platinum-iridium meter prototype based in Paris. The development of stabilized lasers and the methods for determining their frequencies leaded the Conference General des Poids et Mesures to redefine the unit of length in terms of the velocity of light in 1983. In practical measurements, the unit of length is often measured by using optical interferometry. There are several instruments designed to make line scale calibration using laser interferometers, some of them use a photoelectric microscope in order to observe graduation lines. The position of the microscope (or scale) is measured by the laser interferometer [4, 5]. Those measurements can be taken while the microscope is located on the graduation line or dynamically when the