Text color based on contrast against background

Question

I have the following plot:

m <- structure(list(Var1 = structure(c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 
1L, 2L, 3L, 4L, 5L, 6L, 7L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 1L, 2L, 
3L, 4L, 5L, 6L, 7L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 1L, 2L, 3L, 4L, 
5L, 6L, 7L, 1L, 2L, 3L, 4L, 5L, 6L, 7L), .Label = c("FE", "AG", 
"NO", "SPH", "SEP", "H/I", "CMP"), class = "factor"), Var2 = structure(c(1L, 
1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 
3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 5L, 
5L, 5L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 7L, 7L, 7L, 7L, 7L, 7L, 7L
), .Label = c("FE", "AG", "NO", "SPH", "SEP", "H/I", "CMP"), class = "factor"), 
    value = c(0, 0.0419753086419753, 0.172839506172839, 0.0740740740740741, 
    0.0123456790123457, 0.111111111111111, 0.0617283950617284, 
    0.0419753086419753, 0, 0.0765432098765432, 0.0246913580246914, 
    0.00493827160493827, 0.0567901234567901, 0.0320987654320988, 
    0.172839506172839, 0.0765432098765432, 0, 0.175308641975309, 
    0.0197530864197531, 0.177777777777778, 0.120987654320988, 
    0.0740740740740741, 0.0246913580246914, 0.175308641975309, 
    0, 0.00740740740740741, 0.0814814814814815, 0.0395061728395062, 
    0.0123456790123457, 0.00493827160493827, 0.0197530864197531, 
    0.00740740740740741, 0, 0.0197530864197531, 0.00987654320987654, 
    0.111111111111111, 0.0567901234567901, 0.177777777777778, 
    0.0814814814814815, 0.0197530864197531, 0, 0.0716049382716049, 
    0.0617283950617284, 0.0320987654320988, 0.120987654320988, 
    0.0395061728395062, 0.00987654320987654, 0.0716049382716049, 
    0), vtext = c("0.0%", "4.2%", "17.3%", "7.4%", "1.2%", "11.1%", 
    "6.2%", "4.2%", "0.0%", "7.7%", "2.5%", "0.5%", "5.7%", "3.2%", 
    "17.3%", "7.7%", "0.0%", "17.5%", "2.0%", "17.8%", "12.1%", 
    "7.4%", "2.5%", "17.5%", "0.0%", "0.7%", "8.1%", "4.0%", 
    "1.2%", "0.5%", "2.0%", "0.7%", "0.0%", "2.0%", "1.0%", "11.1%", 
    "5.7%", "17.8%", "8.1%", "2.0%", "0.0%", "7.2%", "6.2%", 
    "3.2%", "12.1%", "4.0%", "1.0%", "7.2%", "0.0%")), .Names = c("Var1", 
"Var2", "value", "vtext"), row.names = c(NA, -49L), class = "data.frame")

library(ggplot2)
ggplot(data = m, aes(x = Var2, y = Var1, fill = value, label = vtext)) +
    xlab("") + ylab("") +
    geom_tile() +
    geom_text() +
    scale_fill_gradient(low="white", high="darkmagenta") +
    # Sample code for subtitles: ggtitle(bquote(atop("Age distribution", atop(italic(.(subtitle)), ""))))
    ggtitle(bquote(atop(.(title), atop(italic(.(subtitle)), "")))) +
    theme(axis.text.y = element_text(size = 12), axis.text.x = element_text(size = 12),
          axis.title = element_text(size = 16, face = "bold"),
          plot.title = element_text(size = 20),
          panel.background = element_rect(fill = "white"),
          legend.key.size = unit(0.02, "npc"),
          legend.text = element_text(size = 14),
          legend.title = element_text(size = 16))

Which results in:

The problem, is that the text in the darker squares is difficult to read. Is it possible to change the text color based on the background color, so the text in the clear boxes is black and in the darker boxes is white?

an alternative would be to outline the text; it's a [bit clumsy at R level](https://stackoverflow.com/questions/7734535/control-font-thickness-without-changing-font-size/7735339#7735339), but on devices like gridSVG it might be possible to do it more elegantly. — baptiste, Nov 14 '17 at 18:39

score 18 · Accepted Answer · answered Nov 14 '17 at 08:57

18

Add these two code lines:

geom_text(aes(color = value > 0.1)) +
scale_color_manual(guide = FALSE, values = c("black", "white"))

Here text color depends on value (value > 0.1) and colors are specified with scale_color_manual.

For the output like this:

answered Nov 14 '17 at 08:57

pogibas

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Text color based on contrast against background

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