Comparative Analysis of Low-Cost Portable Spectrophotometers for Colorimetric Accuracy on the RAL Design System Plus Color Calibration Target

Novel low-cost portable spectrophotometers could be an alternative to traditional spectrophotometers and calibrated RGB cameras by offering lower prices and convenient measurements but retaining high colorimetric accuracy. This study evaluated the colorimetric accuracy of low-cost, portable spectrophotometers on the established color calibration target-RAL Design System Plus (RAL+). Four spectrophotometers with a listed price between USD 100-1200 (Nix Spectro 2, Spectro 1 Pro, ColorReader, and Pico) and a smartphone RGB camera were tested on a representative subset of 183 RAL+ colors. Key performance metrics included the devices' ability to match and measure RAL+ colors in the CIELAB color space using the color difference CIEDE2000 <i>ΔE</i>. The results showed that Nix Spectro 2 had the best performance, matching 99% of RAL+ colors with an estimated <i>ΔE</i> of 0.5-1.05. Spectro 1 Pro and ColorReader matched approximately 85% of colors with <i>ΔE</i> values between 1.07 and 1.39, while Pico and the Asus 8 smartphone matched 54-77% of colors, with <i>ΔE</i> of around 1.85. Our findings showed that low-cost, portable spectrophotometers offered excellent colorimetric measurements. They mostly outperformed existing RGB camera-based colorimetric systems, making them valuable tools in science and industry.