IPTEK, Journal of Engineering, Vol. 2, No. 1, 2015 9 The Comparisson between LBP and SQI Methods in the Surface Roughness Measurement Using ESPI Method Mohammad Khoirul Effendi 1 , Agus Sigit Pramono 1 , Pandu Pratama 1 , and Rifki Wardana 1 Abstract Surface roughness measurement using direct contact methods raises several issues, for examples stylus wear and size limitation problems. Furthermore non-contact methods are proposed to solve these problems. One of them is Electronic Speckle Pattern Interferometry (ESPI), which use Helium-Neon (He - Ne) as laser light source. A speckle pattern is produced by scattered light on the surface of the measuring object due to the interference of laser beams, and it will be captured by Charge Coupled Device (CCD) camera. Afterwards Linear Binary Pattern (LBP) and Self Quotient Image (SQI) methods are used to reduce illumination effect in the captured image. The average gray-level from the previous process will be converted into a surface roughness value by gray level to surface roughness conversion formulation. It is obtained from correlation value between gray level and a set of standard roughness. The standard roughness value range is start from 0,05 μm to 12,5 μm. It is measured from five different final machining process, which are flat lapping, grinding, horizontal milling, and vertical milling. As verification, the results of ESPI method will be compared with the result of direct contact tools using Mitutoyo Surftest 301 and 401 Keywords Surface Roughness, ESPI, LBP, SQI, FAR, FRR I. INTRODUCTION 1 uality of a product is determined by several indicators, one of them is the value of surface roughness. In the direct contact method, surface roughness is measured by moving a sensor (stylus) on the surface of the measuring object. Measuring time, the limited size of stylus tip and wear are weaknesses that must be considered when using this method. In the measurement using the direct contact method, the stylus must be driven over the surface slowly to ensure the accuracy. This condition allows surface measuring time in direct contact is longer than indirrect contact method. The limited size of the stylus tip is another factor must be considered. Radhakrishan, 1970 [1] and Mc Cool, 1984 [2] state that the size of the stylus tip has a considerable effect on the accuracy. The accuracy increased by decreasing the size of stylus tip, but in the other side the damage probability will increase too. Poon and Bhushan, 1995 [3], stating the occurrence of damage on the object surface and stylus tip caused by friction each other which is referred as micro-scratches. The occurrence of micro-scrathes in surface roughness measurement lead to inaccurate measurement. In this condition the stylus tip does not measure the roughness value, but also scratch the surface of the measured object. 1 Mohammad Khoirul Effendi, Agus Sigit Pramono, Pandu Pratama, and Rifki Wardana are with Department of Mechanical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia. E-mail: khoirul_effendi@me.its.ac.id; pramono@me.its.ac.id ; rifkiwardhana@ymail.com ; pandutama1989@yahoo.com. As the result, the roughness value will be different in the repeated measurement. Non contact method are method which are developed to solve problem in surface measurement using contact methods. Laser is common light that used as a tool to measure the surface roughness of an object, which is known as Electronic Speckle Pattern Interferometry (ESPI). In the previous study, Rakiman 2007 [4], stated that the influence of illumination is neglected, so that the sampling area for measurement should be selected manually. Furthermore the measurement of the surface roughness can not be done automatically. In this study, the method of Linear Binary Pattern (LBP) and the Self Quotient Image (SQI) will be used as illuminate compensation to increase the accuracy of measurement by compensate the dark side of surface image in order to make measurement runs automatically. II. METHODS In the ESPI method, a laser beam is used to display an image of surface roughness of an object which isthe standard of surface roughness comparator in industry. Afterwards the images are processed through several stages of image processing to produce the gray level values. Finally a converting equation from gray level to the actual surface roughness will be produced. As verification, the results of surface roughness measurements using ESPI method will be compared with the results of direct contact measurement method (Mitutoyo Surftest 306 and 401) to determine the accuracy level of this method. In addition the value of FAR (False Accepted Ratio) and FRR (False Rejected Q