Re: [ferret_users] Palette with different colours about a fixed point

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Samrat,

| I am using Ferret 6.1. I would like to have different colours about a point,
| say 0. For ex:
| 
| fill/lev=(-10,20,1)/pal=newone var
| 
| In this case i would like, say, shades of blue below 0 and shades of red
| above 0. This is possible by explicitly creating a spk file that is defined
| by fixed points. But i would like to use the same palette for other levels
| as well, but all must have shades of blue below 0 and shades of red above 0.

I use the following percentage palette for such cases:

! dark blue -> blue -> red -> dark red
!
   0       0  20  40
  20       0  50 100
  30      45  70 100
  49.999  90  90 100
  50.001 100  90  90
  70     100  45  45
  80     100   0   0
 100      40   0   0

The key here is that there is a jump from light blue "90  90 100"
to pink "100  90  90" across the 50% point.  (I learned this technique
from somebody.)

This jump from light blue to pink is useful when you always need
to know the signs of the values.  But, normally, I don't want
to see too small values and so I have white levels around zero:

! dark blue -> blue -> white -> red -> dark red
!
   0       0  20  40
  20       0  50 100
  30      45  70 100
  44      90  90 100
  44.001 100 100 100
  55.999 100 100 100
  56     100  90  90
  70     100  45  45
  80     100   0   0
 100      40   0   0

Regards,
Ryo