Fig. 1. Several lighting observation conditions specified in DIN 6175-2 standard

Fig. 2. Schematic of experimental device

Fig. 3. Relative spectral energy distribution curves of LED

Fig. 4. Parameter distribution. (a) Color distribution of samples in a^*b^* plane; (b) sparkle grade distribution of samples

Fig. 5. Histogram of image signal intensity distribution under D65 light source

Fig. 6. Results of relevant parameters of the proposed threshold algorithm. (a) Sparkle area fitting; (b) sparkle intensity fitting; (c) sparkle grade fitting

Fig. 7. Visual experiment. (a) Schematic of visual experiment; (b) visual experiment physical picture

Fig. 8. Data analysis. (a) BYKmac data and visual data under light source D65; (b) experimental device data and visual data under light source D65; (c) BYKmac data and visual data under light source A; (d) experimental device data and visual data under light source A