## 2 Literature Review
### Color Landscape
#### 2.1.2 Elements of Color Landscape  
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Hue (H), Saturation (S) and Brightness (B)  
Using color quantitative index HSB data analysis of hue, saturation, and brightness for analyzing landscape color environment has special research significance [4]. It is believed that hue, brightness, saturation of color, and color-area ratio of constituent color can influence color harmony and users' perception of color design [14]. (1) Hue (H) is used to distinguish different types of colors and determine the characteristics of a color landscape, and is the most easily captured by people's vision; (2) Saturation (S) is the freshness of the color perception, reflecting the vividness of the city's colors in the external space, and the purity of a city's color can fully demonstrate ambiguity and express emotion; (3) Brightness (B) refers to the perceived degree of lightness and darkness of colors, and is key objective in urban color visual design [4; 26]. This article uses the HBS as an essential factor to extract color information from photographs for the next step, analysis.  
(2) [leftmargin=*]  
This study adopts the color-area ratio, a color design element in product color design [14], to study landscape color. The color ratio refers to the proportional relationship between each part's length and area in the color combination design [14]. It is produced with the changes in form, position, and space, and plays a decisive role in the overall style and beauty of the color design scheme [27]. Due to the different color ratios, it is possible to create diverse landscape appearances despite using the same color. The proportion of the area occupied by the color greatly influences the effect of color layout in the landscape. [PERSON] and [PERSON] (2019) pointed out that a color layout form should match the users' emotions for product design [15]. All in all, color layout is the spatial arrangement and distribution of colors within a composition, focusing on how colors are positioned relative to each other to achieve visual balance and harmony. In contrast, color ratio pertains to the quantitative relationship between different colors in a composition, emphasizing the proportion of one color to another to create desired visual effects or to convey specific emotions and meanings.  
(3) [leftmargin=*]  
The three constituent colors are main color, auxiliary color, and decorative color, occupying about 70%, 25%, and 5% of the surface area of the product, respectively, which is widely adopted in the color design of color-area ratios [14]. The dominant color features determine landscapes' presentation and visual experience [24]. Urban tones are the overall effect constructed by the three colors and their combined relationships [28], as follows: (1) the primary color is a color that best reflects its cultural and landscape characteristics, which accounts for more than 70% of the ratio, and it has a certain degree of stability and sense of inheritance; (2) the colors that account for more than 20% and less than 70% can be summarized as the city's auxiliary colors, which play a role in color transition and coordination, and are determined by the color co-frequency rule in color design; and (3) the colors that account for less than 5% can be summarized as urban decorative tones, playing a role in highlighting themes.