Disclosed are a cost-effective light source device that can eliminate highlights or hotspots and reduce halo phenomenon on resistor surface and a method for reading resistor value with computer vision, in which an image of a body of a resistor is extracted through irradiation by an annular light source and reflection by a replaceable diffuse reflection hood such as paper box, paper bowl, or paper cup inside pasted with white paper and extraction by an image extraction device, followed by a series of image processing operations conducted by a control unit to calculate a disposition angle of the resistor in an image. Luminous elements on opposite axial ends of the resistor are activated, according to the disposition angle, for illumination, while luminous elements on opposite lateral sides of the resistor are shut down so that a clear color resistor image can be obtained.

A shunt resistor according to the present invention includes a pair of electrode plates spaced apart from each other in a plate surface direction and a resistive alloy plate that connects the pair of electrode plates and that has a predetermined set resistance value. A surface of the resistive alloy plate is provided with a visually recognizable character string pattern that is formed by laser processing and that indicates the set resistance value of the resistive alloy plate, and a surface area and a carving depth of the character string pattern are set in such a manner that the resistive alloy plate has the set resistance value.