I want to use a custom colorscale for a surface plot. I was given a x,y TIFF image with a color bar representing height. I’m trying to reverse engineer the colorscale to back out the heights. I created a function that replicates the color bar fairly well which has allowed me to map the x,y positions to a height. When I plot the surface using the basic example it chooses a color mapping for me. I would like to display it with the original color mapping.
I tried using the examples here and here.
On the basis of this, I figure I could pass a function to colors:
> colors = colorRamp(c("green", "blue", "red"))
> class(colors)
[1] "function"
> sapply(seq(0,1,0.05), colors)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] [,15]
[1,] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 25.5 51 76.5 102
[2,] 255 229.5 204 178.5 153 127.5 102 76.5 51 25.5 0 0.0 0 0.0 0
[3,] 0 25.5 51 76.5 102 127.5 153 178.5 204 229.5 255 229.5 204 178.5 153
[,16] [,17] [,18] [,19] [,20] [,21]
[1,] 127.5 153 178.5 204 229.5 255
[2,] 0.0 0 0.0 0 0.0 0
[3,] 127.5 102 76.5 51 25.5 0
plot_ly(z = ~val_matrix, colors=colors) %>% add_surface()
So I tried my own function:
getR = function(x)
{
if (0<=x & x <=1/3)
{
R = 1
} else if (x>1/3 & x<=1/2)
{
R = 1 - 6*(x - 1/3)
} else
{
R = 0
}
}
getG = function(x)
{
if (0<=x & x<=1/6)
{
G = 1 - 6*x
} else if (1/6<x & x<=1/3)
{
G = -1 + 6*(x)
} else if (1/3<x & x<=2/3)
{
G = 1
} else if (2/3<x & x<=5/6)
{
G = 1 - 6*(x - 2/3)
} else
{
G = 0
}
}
getB = function(x)
{
if (0<=x & x<=1/6)
{
B = 1 - 6*x
} else if (1/6<x & x<=1/2)
{
B = 0
} else if (1/2<x & x<=2/3)
{
B = -3 + 6*x
} else if (2/3<x & x <=5/6)
{
B = 1
} else
{
B = 1 - 6*(x - 5/6)
}
}
x = seq(0,1,2^-10)
cmap = data.frame(
r=sapply(x, getR),
g=sapply(x, getG),
b=sapply(x, getB)
)
ggplot(cmap, aes(x=x)) +
geom_line(aes(y=r), col='red') +
geom_line(aes(y=g), color='green') +
geom_line(aes(y=b), color='blue')
Which gives:
So, I tried
getColor = function(x)
{
r = getR(x)*255
g = getG(x)*255
b = getB(x)*255
return( as.matrix(c(r,g,b), nrow=1, ncol=3) )
}
> sapply(seq(0,1,0.02), getColor)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] [,15]
[1,] 255 255.0 255.0 255.0 255.0 255 255.0 255.0 255.0 255.0 255 255.0 255.0 255.0 255.0
[2,] 255 224.4 193.8 163.2 132.6 102 71.4 40.8 10.2 20.4 51 81.6 112.2 142.8 173.4
[3,] 255 224.4 193.8 163.2 132.6 102 71.4 40.8 10.2 0.0 0 0.0 0.0 0.0 0.0
[,16] [,17] [,18] [,19] [,20] [,21] [,22] [,23] [,24] [,25] [,26] [,27] [,28] [,29]
[1,] 255 255.0 244.8 214.2 183.6 153 122.4 91.8 61.2 30.6 0 0.0 0.0 0.0
[2,] 204 234.6 255.0 255.0 255.0 255 255.0 255.0 255.0 255.0 255 255.0 255.0 255.0
[3,] 0 0.0 0.0 0.0 0.0 0 0.0 0.0 0.0 0.0 0 30.6 61.2 91.8
[,30] [,31] [,32] [,33] [,34] [,35] [,36] [,37] [,38] [,39] [,40] [,41] [,42] [,43]
[1,] 0.0 0 0.0 0.0 0.0 0.0 0 0.0 0.0 0.0 0.0 0 0.0 0.0
[2,] 255.0 255 255.0 255.0 255.0 234.6 204 173.4 142.8 112.2 81.6 51 20.4 0.0
[3,] 122.4 153 183.6 214.2 244.8 255.0 255 255.0 255.0 255.0 255.0 255 255.0 244.8
[,44] [,45] [,46] [,47] [,48] [,49] [,50] [,51]
[1,] 0.0 0.0 0 0.0 0.0 0.0 0.0 0.000000e+00
[2,] 0.0 0.0 0 0.0 0.0 0.0 0.0 0.000000e+00
[3,] 214.2 183.6 153 122.4 91.8 61.2 30.6 5.662137e-14
> print(class(getColor))
[1] "function"
> plot_ly(z = ~val_matrix, colors=getColor) %>% add_surface()
Error in grDevices::rgb(results, maxColorValue = 255) :
at least 3 columns needed
I also tried switching nrow and ncol and get the same error.