# define a sequential discrete color map with first color white.

43 views (last 30 days)
Damith on 15 Apr 2015
Answered: Makarand on 27 Apr 2018
Hi,
I need to define a color map with 8 different sequential discrete colors like below. But, the first colot should be while. How can I define a color map and include in the MATLAB code below.?
Any help is highly appreciated.
figure;
pcolor(lon,lat,t2);
colorbar

Image Analyst on 15 Apr 2015
Try this:
cmap = jet(20)
cmap = flipud(cmap(1:10,:));
cmap(1,:) = [1,1,1];
colormap(cmap);
colorbar
Damith on 15 Apr 2015
Thanks. I tried it. This is more close to what I wanted. See the modified code below and the figure it produced.
Few more things I need to accomplish.
1) I need to remove the tick marks from the colorbar but it has not removed even the last 3 lines in the code intended to do.
2) I need to graduate the colorbar from 0 (zero) to 20.
3) I need to know whether I can place the colorbar bottom of the figure?
Any help is appreciated to accomplish the above tasks.
Thanks.
figure;
pcolor(lon,lat,t2);
cmap = jet(20);
cmap = flipud(cmap(1:10,:));
cmap(1,:) = [1,1,1];
colormap(cmap);
hcb=colorbar
set(hcb,'YTick',[])
colorbar
Image Analyst on 16 Apr 2015
Do you know the RGB values for each of the 10 colors? If so, just assign them to each row of cmap.

Chad Greene on 16 Apr 2015
Edited: Chad Greene on 16 Apr 2015
The colormap you uploaded in your original question looks a lot like a Cynthia Brewer colormap, which Stephen Cobeldick has made into a nice little function called brewermap. You'll notice the first value in that colormap you uploaded is not pure white. Here's how you can create the 8-level brewer map with the brewermap function, and if you want to force the first value to white, you can do that too.
pcolor(3.5*abs(peaks(1024)))
% Create colormap:
map = brewermap(8,'GnBu');
map(1,:) = [1 1 1]; % optionally force first color to white
colormap(map)
cb = colorbar('location','south');
caxis([0 20]) % sets colorbar limits
set(cb,'xtick',[])
% another colorbar:
cb2 = colorbar('location','northoutside');
The reason your set(hcb,'YTick',[]) did not work is because you followed it by calling a new colorbar. And you can set the colorbar limits from 0 to 20 by caxis([0 20]). For colorbar location you may alternatively want 'southoutside'.

Makarand on 27 Apr 2018
if you have unequal intervals then you can check Recolor_pcolor