Why set up three character lists to represent density?

[zhangluustb]

Why set up three character lists to represent density?And How to calculate density？

[zhangluustb]

The first two character lists are not used in the source code？

[joelibaceta]

In the readme I explain how I calculate the color intensity from rgb, according to this I assign a character from a range of values, por example If I have 5 characters:

Char	Intensity Factor
.	0 .. 50
:	51 .. 101
~	102 .. 152
+	153 .. 203
@	204 .. 255

[joelibaceta]

The three set of chars are used by three different render strategies.