define a sequential discrete color map with first color white.

Question

Damith 2015-4-15

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回答： Makarand 2018-4-27

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.

Thanks in advance.

figure;
pcolor(lon,lat,t2);
shading interp
colorbar

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Answer 1

Image Analyst 2015-4-15

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在 MATLAB Online 中打开

Try this:

cmap = jet(20)
cmap = flipud(cmap(1:10,:));
cmap(1,:) = [1,1,1];
colormap(cmap);
colorbar

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Damith 2015-4-15

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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);
shading interp
cmap = jet(20);
cmap = flipud(cmap(1:10,:));
cmap(1,:) = [1,1,1];
colormap(cmap);
hcb=colorbar
set(hcb,'YTick',[])
colorbar

Image Analyst 2015-4-16

Do you know the RGB values for each of the 10 colors? If so, just assign them to each row of cmap.

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Answer 2

Chad Greene 2015-4-16

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编辑：Chad Greene 2015-4-16

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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)))
shading interp
% 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'.