Re: Histograms with fill solid and monochrome Postscript

[Philipp K. J. <ja...@ie...>]

Ok, apparently we really misunderstood each other.
Let me try again.

If I say:
	set style fill pattern
	set style histogram clustered
	set style data histogram
	plot "data" u 1, "" u 2, "" u 3

gnuplot will iterate through the available patterns
for data in column 1, 2, and 3.

If instead I say
	set style fill solid
	...
gnuplot will iterate through the available colors
(red, green, blue, ...)

But what if I want a monochrome output? I can't 
use red, green, blue, .... Instead I must use shades
of gray. 

What I therefore want is for gnuplot to iterate through 
densities:  not patterns, not colors. Just a single color, 
but different densities of that color.

I wonder whether there is currently support for that.

Best,

		Ph.



On Wednesday 30 July 2008 22:03, you wrote:
> On Wednesday 30 July 2008, Philipp K. Janert wrote:
> > What I hear you say here is this, I think:
> >
> > Gnuplot has a way to automatically select
> > different fill patterns (which will work in B&W),
> > and different fill colors (which require a color
> > terminal).
>
> Both, actually. It's your choice whether to use colors
> or fill-patterns or both.
>
> > But gnuplot does NOT have a way to automatically
> > select different monochrome fill densities. To
> > achieve such an effect, I have to start hacking
> > Postscript.
>
> No, I didn't intend to say that at all.
> I may have misunderstood your question.
> I thought you were asking about how you might print a
> previously-created PostScript file on a monochrome printer
> even though it was originally created using color.  I explained
> one wasy to do this.
>
> If you are asking instead how you could create halftone output in
> the first place, that's a different question.  What exactly are
> you trying to do?  There may well be several alternatives available.
>
> > What we really would want is something that cycles
> > through fill densities, in the same way that gnuplot
> > cycles through line types.
>
> I think that is possible now, although perhaps not as conveniently
> as you would like.
>
>   # Define a set of sequential gray values
>   set style line 101 lc rgb "grey10"
>   set style line 102 lc rgb "grey70"
>   set style line 103 lc rgb "grey20"
>   set style line 104 lc rgb "grey80"
>   ...
>   set style increment user # horrible syntax, but it's what we've got
>
>   set style histogram cluster
>   set style fill solid 1 noborder
>
>   plot newhistogram lt 101, for [i=1:10] 'datafile' using i with histogram
>
> > Alternatively, we could have user-defined "fill styles",
> > and then gnuplot could cycle through those. This way,
> > users can define either a set of color fill styles, or
> > monochrome density fill styles (or any combination
> > thereof), and gnuplot would cycle through those. (I
> > have no idea how hard that would be, and I would not
> > think it is high priority, though.)
>
> Adding a mechanism to re-map the order of existing fill patterns would be
> easy. What seems well-nigh impossible is to provide a terminal-independent
> way of defining new fill styles.
>
> 	Ethan
>
> > On Wednesday 30 July 2008 19:05, you wrote:
> > > On Wednesday 30 July 2008, Philipp K. Janert wrote:
> > > > Let's say I am trying to generate histograms
> > > > like this:
> > > >
> > > > set style fill solid
> > > > set style histogram clustered
> > > > set style data histogram
> > > > plot "data" u 1, "" u 2, "" u 3
> > > >
> > > > I get a plot of histograms, with each "bin"
> > > > in a different color (red, green, blue).
> > > >
> > > > Now, I would like to export this to a monochrome
> > > > Postscript terminal. I would expect that the colors
> > > > are mapped to different levels of grayscale.
> > > >
> > > > Instead, all colors seem to be mapped to black
> > > > (or very nearly black).
> > > >
> > > > Is there a way to achieve the kind of automatic
> > > > color-to-grayscale mapping I envision, or is this
> > > > currently not supported?
> > >
> > > The issue is that there are two uses of color.
> > >
> > > One is to create a palette that captures a continuous quantity.
> > > To convert this to a monochrome plot you want a greyscale mapping,
> > > and that's what the postscript terminals do if you select "mono".
> > >
> > > The other use of color is simply to differentiate object A from
> > > object B.  Here a greyscale is irrelevant, and you instead want
> > > some mapping that makes the common colors maximally distinct from
> > > each other.
> > >
> > > I suggest that a clever way to achieve the latter goal is to
> > > in this case redefine the PostScript  setrgbcolor operator so
> > > that you get an NTSC (black-and-white TV) mapping of the colors.
> > > One line in the PostScript prolog suffices for this, so local
> > > modification without touching the gnuplot executable is very
> > > easy.  I've posted complete instructions several times, but
> > > I don't seem to have saved a copy on my local disk.