COTTON-COLOR INSTRUMENTATION ACCURACY: TEMPERATURE AND CALIBRATION PROCEDURE EFFECTS

Abstract

Government cotton classing offices and gins with state-of-the-art process-control systems conduct automatedcotton-color measurements. Calibration of the color instrumentation involves the use of five colored ceramic tiles asreferences for input to a multiple-linear-regression model. In this study, two commercial color-measurement instrumentsrecorded color values of a set of 18 colored ceramic tiles at various time intervals. The effects of calibrating with fewer ofthe calibration tiles, of using a simpler calibration algorithm, and of temperature fluctuation, were determined regardinginstrument accuracy. Both methods of simplifying calibration (reducing the number of tiles and using a simple-linearmodel) had the same effect: better accuracy in the brightness measurement (Rd) and lower accuracy in the yellownessmeasurement (+b). Whereas +b is the more critical measurement, the multiple-linear model with four or five tiles issuperior overall. However, the difference is not so great as to render the simple-linear model with only two tilesinadequate in a process-control system that demands greater simplicity. Temperature changes were found to be correlatedwith changes in measured color values. The measured value of Rd trended downward with increasing temperature, butthere was no predictable trend in measured +b. Use of similar color instrumentation in a cotton gin would require somemethod of compensation for temperature effects.