Color calibration of scanners for scanner-independent grain grading

Scanner technology is emerging as a cost-effective and robust imaging alternative to camera-based systems in many applications. However, scanner technology is changing so fast that image quality can vary from model to model. It is critical that images scanned with different scanners be brought to a common basis for processing and measurement through a calibration process that eliminates scanner-to-scanner variability. The focus of this research was to investigate scanner-to-scanner variability and develop color correction or mapping functions to allow for machine-independent grain inspection. Various makes and models of scanners were compared for optical and color characteristics. Three different color correction methods were evaluated: grayscale (GS) transformation, redgreen-blue (RGB) transformation, and histogram matching. All three models of color correction worked within satisfactory tolerance for a multicolor Q60 chart. However, for grain samples of a limited color range, the histogram matching approach performed better than GS and RGB transformations for scanner calibration. The color-corrected test images matched the reference images within 3 grey values. Differences between the three models of color correction are discussed.