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

[Samrat Rao <samrat.rao@xxxxxxxxx>]

Hi Ryo,

Sorry for the late reply, but to me it seems that the setting up of the colour palette by percentages can give shades of blue to red about zero only if the upper and lower limits of the levels qualifier are equal.

That is,
fill/lev=(-10,10,1)/pal=ryo_pal var
gives shades of blue below 0 and shades of red above 0.

But,
fill/lev=(-10,20,1)/pal=ryo_pal var
will not give shades of blue below 0 and shades of red above 0 as this is a percentage based palette.

I was wondering if without specifying explicitly the value points in a palette it is possible to always have  shades of blue below 0 and shades of red above 0. This enables me to use the same palette each time without making any changes to it regardless of how negative or how positive the limits are.

Hope i am more clear now.

Thanks,
Samrat Rao.

On Wed, Jan 6, 2010 at 11:15 PM, Ryo Furue <furue@xxxxxxxxxx> wrote:

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