如何在R中管理颜色对比度，以便标记曲线图和表格？

Question

R中的颜色对比是如何工作的？我假设在颜色十六进制值中有一些触发器，可以用来帮助判断是否应该将标签的颜色更改为更亮/更暗的颜色。我对一个通用的解决方案很感兴趣--我知道有一些软件包可以实现ggplot2的色彩对比度控制。我更喜欢一种可以控制颜色对比度的方法。

这段代码说明了这一点。scales包处理颜色对比度非常好。我只是想对它有更多的控制。

 library(tidyverse)

    library(scales)

    show_col(c("darkred", 
               "wheat", 
               "darkblue", 
               "steelblue"))



tibble(key = letters[1:4], 
       value = 1:4) %>%
  ggplot(aes(key, value))+
  geom_col(aes(fill = key))+
  geom_text(aes(label = key), 
            position = position_stack(vjust = 0.5))+
  scale_fill_manual(values = c("darkred", 
                           "wheat", 
                           "darkblue", 
                           "steelblue")) 

来自scales

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来自ggplot

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Answer 1

@Henrik指出，开源的魔力意味着我可以从scales包中获得代码并在其上构建，以实现我的目标。

library(tidyverse)
library(scales)

# Create colour vector
colours <- c("steelblue", 
  "wheat", 
  "darkblue", 
  "darkred") 


### Code from scales package use switch from white/black based on colour specification

## grab matrx of hcl. According to ?hcl, 
## stands for hue, chroma and luminance
hcl <- farver::decode_colour(
  colours, "rgb", "hcl")

## Simple ifelse statement to create binary 
## colour vector based on conditional value
## of luminance that is higher than 50. 
label_col <- ifelse(hcl[, "l"] > 50, "black", "white")


## back to ggplot2 example


## 1) Use borrowed scales code to create a 
## simple wrapper function called contraster
contraster <- function(.colours){
  
  .colurs_hcl <-  farver::decode_colour(
    .colours, "rgb", "hcl")

  ifelse(.colurs_hcl[, "l"] > 50, "black", "white")
}

colours <- c("steelblue", 
             "wheat", 
             "darkblue", 
             "darkred") 

# 2) Now re-create the data and plot
tibble(key = letters[1:4], 
       value = 1:4) %>%
  ggplot(aes(key, value))+
  geom_col(aes(fill = key))+
  geom_text(aes(label = key),
            color = contraster(colours),
            position = 
              position_stack(vjust = 0.5))+
  scale_fill_manual(values = colours) +
  labs(title = "Label colours are now contrasting with the background")

​

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