Friday, August 24, 2012

Converting from a hex-string color to its rgbvalue

There are several ways to specify color when one plots using gnuplot.Among them hex-string (like "#0000ff") and rgbvalue (like "256") specification is very important. In this post we will talk about converting from a hex-string color to its rgbvalue (the inversion will be talked in another post).

#pick the red color hex string out
red(colorstring)= colorstring[2:3]
#pick the green color hex string out
#pick the blue color hex string out
#convert a hex string to its dec format
#calculate the rgb value from the r,g,b weight
rgb(r,g,b) = 65536*int(r)+256*int(g)+int(b)
#convert the hex color string to its rgb value.
set term png
set output "hex_string2rgbvalue.png"
plot 'color.dat' u 1:2:(hex2rgbvalue(stringcolumn(3)))\
              w lp pt 7 ps 3 lc rgb variable notitle
set output

File 'color.dat' has content like the following:
0 1 #ff0000
1 2 #00ff00
2 3 #0000ff
3 4 #ff00ff
4 5 #ffff00
5 6 #00ffff
0 6 #00ffff
1 5 #ffff00
2 4 #ff00ff
3 3 #0000ff
4 2 #00ff00
5 1 #ff0000

The output file 'hex_string2rgbvalue.png' looks like this:
Fig.1 Converting from a hex-string color to its rgb-value

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