Appearance is critical for metal finishers such as Light Metals Coloring (LMC; Southington, CT, USA) that apply gold or clear (silver) anodized finish to decorative caps on perfume bottles. Obtaining the correct color is imperative, but variations in the anodizing process can cause color variations. "The process of bulk anodizing has variability," says John Schune-mann, president of Thames Engineering and Design (Wa-terford, CT, USA), "so there is variation in how the final part will appear. "Indeed," he says, "maybe 7% to 10% of the parts are hardly colored at all!" In the past, inspectors sat next to a conveyor to inspect gold-anodized parts, a job that was labor-intensive and impossible to perform without making mistakes. LMC hired Thames Engineering to develop an automated inspection system to replace the human inspectors. Although the company has C++ image-processing capability, Thames decided to tap the experience of engineers at Bloomy Controls (Windsor, CT, USA), who had previously used Lab-View software from National In-struments (NI; Austin, TX, USA). Bloomy Controls found that it is easier to perform color inspection when the pixel data are expressed in hue-saturation-luminance (HSL) color space, rather than RGB coordinates.
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