Re: conditional text color?

[Juhász P. <pet...@gm...>]

On Mon, 2026-03-23 at 11:57 -0400, Allin Cottrell via gnuplot-beta
wrote:
> I have a gnuplot routine that shows a correlation matrix as a heat 
> map. If the dimension of the matrix is not too great it prints the 
> value of the correlation coefficient in each "cell". Mostly this 
> works fine, but if the color of the cell is a relatively dark blue 
> (indicating a strong negative correlation) the default black text is 
> not very legible. So I'd like to make the textcolor conditional.
> 
> At present I have this plot statement:
> 
> plot $data matrix with image, $data matrix using \
>   1:2:(sprintf("%.1f",$3)) with labels
> 
> I'd like to append something like
> 
> tc $3 < -0.6 ? rgbcolor "white" : rgbcolor "black"
> 
> That doesn't work ("colorspec option not recognized", not very 
> surprisingly). But is there a way to do this?
> 
> Thanks for any guidance.

Hi,

AFAIK the labels style supports variable color. So you should be able
to do something like

$d << EOD
1 2 foo 0.3
2 3 bar 0.7    
EOD

plot $d u 1:2:3:($4 > 0.6 ? 0xe00000 : 0x00e000) w labels tc rgb var

In this case you'd have to specify the colors as integers, which may be
slightly inconvenient and unmaintainable. 
Other forms work too, like `tc variable` which would set the colors
based on the numbered color styles (same as used for functions/data by
the plot command), or `tc palette`, which draws colors according to a
color palette (either the default or the one you can set up before the
plot). This palette mode also draws a colorbar by default which you
have to disable if you don't want it.

So you have many options, neither of which is exactly what you want.

best regards,
Peter