This paper presents an investigation into the color space and the recognition methodology for developing a non-contact approach to reading the value of a resistor by identifying the color bars from its color image. In this work, several color spaces for measuring colors are evaluated and compared. The uniformed color space known as the CIE-LAB color space is found to exhibit good properties for color recognition task. Hue(H)-Saturation(C)-Intensity(V) color space, which are calculated from CIE-LAB color space, provides an intuitive measure of color. Two color identification methods are investigated. The first method uses the Bayes classifier which defines color boundaries based on the variances of colors. The second method uses predefined fixed color region boundaries. A color is identified if it falls within a color region. A combination of both methods can achieve reliable recognition of color bars and hence correct resistor value can be derived.
Kap Luk Chan,
"Reading resistor values by color image processing", Proc. SPIE 3185, Automatic Inspection and Novel Instrumentation, (18 August 1997); doi: 10.1117/12.284040; https://doi.org/10.1117/12.284040