<p>Lubricating oils have been used in various machines and are essential for the normal operation of the machines. Still, they degrade with operation time, and various lubricating oil analyses are performed in the field. Notably, monitoring solid particles in lubricating oil is important because solid particles significantly impact the machine's life. Thus, analyses of solid particles in lubricating oil have been widely used in the field, whereas these analyses still leave room for improvement in terms of cost and convenience. Therefore, we developed a Lubricating oil Image Analysis (LIA), which uses the color information of the lubricating oil itself. This method makes it possible to indirectly monitor the residual rate of oxidation inhibitors by RGB values and is expected to be used in the field for lubricating oil analysis easily and at a low cost. In this study, we proposed on-site measurement technology for solid particles in lubricating oil by binarization as a new diagnostic technology for LIA and investigated its usefulness. Consequently, the binarized area ratio made it possible to diagnose the degree of contamination of lubricating oil. Additionally, the particle diameter distribution by binarization has high sensitivity over a relatively large particle diameter range. Furthermore, it was shown that particle measurement using LIA can quantitatively evaluate sludge in simulated oxidized oil with different degrees of oxidation.</p>