Efficient Color Quantization Using Superpixels

We propose three methods for the color quantization of superpixel images. Prior to the application of each method, the target image is first segmented into a finite number of superpixels by grouping the pixels that are similar in color. The color of a superpixel is given by the arithmetic mean of the colors of all constituent pixels. Following this, the superpixels are quantized using common splitting or clustering methods, such as median cut, k-means, and fuzzy c-means. In this manner, a color palette is generated while the original pixel image undergoes color mapping. The effectiveness of each proposed superpixel method is validated via experimentation using different color images. We compare the proposed methods with state-of-the-art color quantization methods. The results show significantly decreased computation time along with high quality of the quantized images. However, a multi-index evaluation process shows that the image quality is slightly worse than that obtained via pixel methods.

[Study on quality identification of Curcumae Rhizoma from different origins based on quantitative analysis of appearance color and content of main components]

L~*, a~* and b~* values of prepared slices of Curcumae Rhizoma were measured by spectrophotometer. SPSS 21.0 was used for discriminant analysis to establish the color range and mathematical prediction model of prepared slices of Curcumae Rhizoma. The values of L~*, a~* and b~* of kwangsiensis ranged from 58.09-62.40, 4.53-5.66 and 23.61-24.29, while the values of L~*, a~* and b~* of phaeocaulis were between 64.02-70.71,-0.89-4.13 and 44.59-54.52, respectively. The values of L~*, a~* and b~* of wenyujin were 68.55-70.99,-0.11-1.47 and 28.26-32.19, respectively. The mathematical prediction model was proved to be able to realize 100% identification of Curcumae Rhizome of different origins through original and cross validation and external samples validation. A dual wavelength HPLC was established; the contents of 9 sesquiterpenoids and 3 Curcumae Rhizomes were determined simultaneously; and the contents of Curcumae Rhizome of different origins were determined. The results showed that kwangsiensis had higher contents of neocurdione, β-elemene and isocurcumaenol, phaeocaulis curcumin, furadienone, demethoxycurcumin and curcumin; and wenyujin mainly contained curdione, furadienes and guimarone. Pearson correlation analysis on L~*, a~*, b~* value and content of 12 components showed that curcumin, furadienone, demethoxycurcumin and curcumin had a significant positive correlation with b~* value(P<0.01). There was a significant negative correlation between neocurdione, β-elemene and isocurcumaenol and L~* value(P<0.01). Curdione, furadienes and guimarone were significantly correlated with L~* value(P<0.01),indicating that the appearance co-lor of Curcumae Rhizoma could reflect the change of the content of the internal components. This study provided reference for the rapid recognition of Curcumae Rhizoma and the establishment of quality evaluation system.

[Color quantification and evaluation of landscape aesthetic quality for autumn landscape forest based on visual characteristics in subalpine region of western Sichuan, China]

Evaluation of landscape aesthetic quality is a key step in the management system of forest resource. Color is an important component of autumn landscape forest, and quantitative analysis of color and scientific evaluation of landscape aesthetic quality are important for the management of autumn landscape forest. We assessed the aesthetic quality of autumn landscape forest using scenic beauty estimation and analyzed the effects of color characteristics on ornamental value of autumn landscape forest based on color composition and color spatial pattern according to human's visual characteristics. The results showed that the overall landscape quality of subalpine region of western Sichuan could be divided into five grades according to beauty value (I to V). About 71.5% of autumn landscape forests could be classified into grade I, II, and III, indicating that autumn landscape forests of subalpine region in western Sichuan had higher ornamental value. According to the scenic beauty estimation value, the landscape aesthetic quality of broadleaved mixed forests was higher than that of coniferous and broadleaved mixed forests and pure forests. In terms of the comprehensive index evaluation system of color elements, the index weight coefficient order was landscape patch heterogeneity factors>autumn main color factors>color saturation and brightness factors>color diversity and evenness factors. With cluster analysis, autumn landscape forests of western Sichuan could be divided into three types. The forests with higher ornamental value showed following characteristics: larger degree of patch fragmentation and heterogeneity, higher percentage of orange and yellow and lower percentage of green in autumn, higher percentage of color saturation and brightness, and higher color diversity and uniformity index. The communities with higher richness, species diversity and evenness index would have higher beauty values. We concluded that species diversity and fragmentation of colors should be considered in the construction of autumn landscape forests, and that aesthetic quality of autumn landscape forest could be improved by planting and cultivating tree species with various and bright autumn leaf colors.