Small Color Differences in the Very Pale and Dark Grayish Regions Measured by Camera

Abstract

The camera capability to measure small color differences between sample pairs is evaluated by comparing the camera performance with a reference instrument. To this end, the appropriate working conditions are established, the camera spectral sensitivities and imaging noise are characterized, and the transformation to obtain a device independent representation of color is calculated considering two approaches: one, on the basis of the camera spectral sensitivity (CSS), and two, on the basis of the unified measure of goodness of the camera (UMG) that involves an imaging noise model. The camera performance is assessed from the measurement results of a large number of varied small color differences in the very pale and the dark grayish color regions, the involved uncertainty, the absolute discrepancy, and the relative discrepancy with respect to the reference instrument. In the experimental application, the three CCD camera SONY DX-9100P is assessed and compared with the spectroradiometer Photo Research PR-715 as reference instrument. The results reveal a high quality performance of the camera system, with absolute discrepancies in the estimation of color differences around the camera tolerances (CIELAB 0.5ΔE*ab or CIEDE2000 0.6 ΔE00). The color uniformity in textile dying is evaluated by analyzing some pairs of extreme center fabric samples. Although the camera is more sensitive to the texture effects than the spectroradiometer, both instruments yield consistent and satisfactory Pass/Fail results.