RGB CALIBRATION FOR COLOR IMAGE-ANALYSIS IN MACHINE VISION

A color calibration method for correcting the variations in RGB color values caused by vision system components was developed and tested in this study, The calibration scheme concentrated on comprehensively est imating and removing the RGB errors without specifying error sources a nd their effects, The algorithm for color calibration was based upon t he use of a standardized color chart and developed as a preprocessing tool for color image analysis, According to the theory of image format ion, RGB errors in color images were categorized into multiplicative a nd additive errors, Multiplicative and additive errors contained vario us error sources-gray-level shift, a variation in amplification and qu antization in camera electronics or frame grabber, the change of color temperature of illumination with time, and related factors, The RGB e rrors of arbitrary colors in an image were estimated from the RGB erro rs of standard colors contained in the image, The color calibration me thod also contained an algorithm for correcting the nonuniformity of i llumination in the scene. The algorithm was tested under two different conditions-uniform and nonuniform illumination in the scene, The RGB errors of arbitrary colors in test images were almost completely remov ed after color calibration, The maximum residual error was seven gray levels under uniform illumination and 12 gray levels under nonuniform illumination. Most residual RGB errors were caused by residual nonunif ormity of illumination in images, The test results showed that the dev eloped method was effective in correcting the variations in RGB color values caused by vision system components.