Re: too coarse stepping when plotting color box

[Manfred S. <man...@gm...>]

Hi Ethan,

> 
> After playing around with non-linear discrete palettes like the one in your
> problem figures, I have become suspicious that the problem is more serious
> than just the resolution of the color box.  The palette colors assigned to
> individual points are also wrong.  That is, the bad coloring in the color box
> is a correct representation of the coloring assigned to elements of the plot.
> 


Yes, I found that changing this colorbar code, it changes also the the
plot itself, perhaps because of the "set_color(gray);" line inside of the loop?


> Now it may be that the way I constructed a test palette is not a good way
> to do it.  I'll show my test below.  
> 
> set palette defined (0 "purple", 1 "blue", \
>                      1 "blue", 2 "dark-green", \
>                      2 "dark-green", 4 "spring-green", \
>                      4 "spring-green", 8 "yellow", \
>                      8 "yellow", 16 "orange", \
>                      16 "orange", 32 "red" \
>                      )
> set xrange [0:32]
> set cbrange [0:32]
> set ytics 2
> set cbtics 2
> set grid y
> 
> plot '+' using 1:1:1 with points lt 7 lc palette
> 
> pause -1
> 
> # Limiting the number of colors makes it much worse, and clarifies that the
> # error comes from assigning colors to the palette in equal increments
> # rather that looking at the requested range boundaries:
>   set palette maxcolors 7
>   replot
> 
> 
> So apparently one cannot create a discrete palette this way.
> Or at least you cannot create a discrete palette with unequal color ranges.
> Using "show palette palette 7" confirms this, I think.
> 
> But maybe there's another way that works better.
> Perhaps you could create a palette by hand and load it using
>  set palette file 'mypalette.dat'
> Unfortunately the documentation is not very helpful as to exactly how color
> ranges are assigned to colors that are read in from a file.
>  
> What commands produced the palette in your problem case?



I did something along this (I want to change colors exactly at
values 1,2.5,5,10,....200):

set term png truecolor small size 770,610
set out "|cat"
set pm3d map
s=-1.0
d=200-(-1.0)
set palette defined (  0.0 "#DDDDDD", (-0.01-s)/d "#DDDDDD", \
               (-0.01-s)/d "white",     (1.0-s)/d "white",  \
                 (1.0-s)/d "#FFFF00",   (2.5-s)/d "#FFFF00",  \
                 (2.5-s)/d "#C1FFB4",   (5.0-s)/d "#C1FFB4",  \
                 (5.0-s)/d "#92E178",  (10.0-s)/d "#92E178",  \
                (10.0-s)/d "#6EC36E",  (20.0-s)/d "#6EC36E",  \
                (20.0-s)/d "#49913C",  (30.0-s)/d "#49913C",  \
                (30.0-s)/d "#577350",  (40.0-s)/d "#577350",  \
                (40.0-s)/d "#5050C8",  (50.0-s)/d "#5050C8",  \
                (50.0-s)/d "#6600AA", (100.0-s)/d "#6600AA",  \
               (100.0-s)/d "#993399", (150.0-s)/d "#993399",  \
               (150.0-s)/d "#AA3366", (199.99-s)/d "#AA3366", (200.0-s)/d "#FF66FF" )
set cbrange [-1.0:200]
splot [:][:][:] '/tmp/mydata' matrix notitle
set output


> 
> 	Ethan
> 
> 
>> As Dan suggested, if there are only 5 colors in the palette then we need
>> only draw 5 rectangles in the color box. Unlike the current code,
>> however, they shouldn't be evenly spaced.  The endpoints of each rectangle
>> should be taken from the palette definition so that they will indeed be
>> placed with perfact accuracy.
>>
>> 	Ethan
>>
>>>