Smooth gradient mapping of a function of two (xy) variables in gnuplot?
I would like to show the values of a function of two variables, for example x+y
, as an image of a "bitmap". So I tried this based on http://gnuplot.sourceforge.net/demo/heatmaps.html :
# Color runs from white to green
set palette rgbformula -7,2,-7
set cbrange [-5:5]
set cblabel "Value"
unset cbtics
set xrange [-4.5:4.5]
set yrange [-4.5:4.5]
set view map
splot x+y with image
... but getting nothing:
$ gnuplot -persist test.gp
"test.gp", line 45: warning: Image grid must be at least 2 x 2.
So how can I get the "pixel" at, say x = -2, y = -2, by color according to x+y
= - 4 by cbrange
?
Edit: it worked out:
set palette rgbformula -7,2,-7
set cbrange [-5:5]
set cblabel "Value"
unset cbtics
set xrange [-4.5:4.5]
set yrange [-4.5:4.5]
set pm3d
unset surface
set view map
splot x+y
Outputs:
But - let's say I want the gradient in this range to be exported as a "smooth" gradient (no axes, ticks, marks of any kind) on a large PNG, say 3000x2000 pixels; what would be the best way to achieve this?
source to share
Starting with your edit: you just deactivate everything. Value:
unset colorbox
unset xtics
unset ytics
set border 0
Then by id you create a list of commands:
set palette rgbformula -7,2,-7
set cbrange [-5:5]
unset cblabel
unset cbtics
set xrange [-4.5:4.5]
set yrange [-4.5:4.5]
set pm3d
unset surface
set view map
unset colorbox
unset xtics
unset ytics
set border 0
splot x+y
You only get a gradient
EDIT: To improve the gradient step and create a smoother image, you need to use pm3d
interpolate
.
set pm3d interpolate 4,4
source to share