map with positive & negative values

[gsescousse]

Hello,
I have a functional map which contains both positive & negative values, and I want to see all of them using a different color code for positive & negative values. I have played around with the "palette", but couldn't find the right one to display positive & negative voxels when superimposed on a anatomical template. The problem seems to be that when using a single palette, all the values equal to zero (i.e. transparent) are assigned a color (the one in the middle of the palette), which makes the underlying anatomical template appear in this color. The only solution I have found so far is to create a duplicate of the map, use 2 different palettes and set the min & max values so that one palette codes for positive values, and the other one codes for negative values...
As this solution is not 100% satisfying, I was wondering whether there was a simpler answer to my problem...
Thank you very much !
Guillaume

[riviere]

Hi Guillaume,
I'm not really sure to exactly understand what you want to do, but I guess you would like to assign a particular color (or palette position) to the value 0, then stretch independantly positive and negative palette values ?
Well, then you're right, there is no easy way to do it in anatomist palette settings interface... Palette edition interface needs to be improved, but it's quite a fastidious and time-consuming work...
The way we generally do in such a situation is to use symmetrical settings for negative and positive values: assume 0 is in the middle of the palette, then set the same absolute value for min and max (for instance -156 and 156): this way 0 will always get the same color. You can always set the exact value you want for min/max bu typing the values in the edition boxes then set the min/max cursors to their most left/right positions.
But of course it's not an ideal solution, I admit...
This issue will not be impoved in the next version, sorry...
Denis

[gsescousse]

Hi Denis,
thank you very much for your detailed and quick answer. I'm sorry I haven't been able to make myself totally clear, though in the end your answer was relevant to my question. I tried what you suggested (and for me it would be an ideal solution ), but the problem is that I couldn't find a palette with a thin white band in the middle that I could assign to voxels with a 0. The color in the middle is always non-white, and then when my functional map is fusioned with an anatomical template, the anatomical template appears in that non-white color.
Hence the solution I have found: using 2 objects of the same map, and choosing for each of them a different palette, one that has a white band at one end of the color spectrum, an the other that has a white band at the other end. I then set the min/max values so that one palette only shows negative values (e.g. -156 & 0) and the other one shows positive values (0 & 156).
I hope I'm being clearer than yesterday... But from your answer I have the feeling this solution is the simplest one in the end (but don't worry, when I said "not 100% satisfying", I meant "98 % satisfying", as I find very handy all the other features of Anatomist ).
Thank you again for your time and help.
Guillaume

[riviere]

Yes, anatomist lacks some palettes for positive/negative values. You can draw one using your favorite image drawing software (gimp, photoshop or whatever) and save it in your $HOME/.anatomist/rgb/ directory (create it if it doesn't exist). Then go to <settings>/<reload palettes> or restart anatomist to see it in the palettes list.
If you have a nice palette, you can send it to us, we could add it to the "standard" palettes list.
Denis

[gsescousse]

Hi Denis,
Thank you very much for your answer.
Then I will look into creating my own palette, and if it is nice enough I'll send it to you...
Guillaume