How to specify the colors within a colorbar

Hello all,

I am having problems setting the face color of my colorbar.

I have a range of data points color coded based on an underlying variable (example below is based on points ranging between Red - Yellow). While I can specify the value limits of the color bar, I am having trouble specifying the exact face color to be displayed on the color bar.

I have tried to directly edit within the color bar editor - but to no avail.

Any help would be much appreciated.

[Image Analyst]

You've not given us much to go on. So just make up an N by 3 array of values in the range 0-1 and use the colormap() and colorbar functions. You might also use caxis(). A more descriptive question may get you a better answer.

[Caroline Whyatt]

Thank you Image Analyst. I have a N x 3 color array that specifies the face color of each data point. Unfortunately, I am seem to be having problems specifying the face color of the associated Color Bar.

For example,

x=[1,2,3,4];
y=[5,6,7,8];
sz=[100,100,100,100];
Color=[1,1,0;
    1,0.666666666666667,0;
    1,0.333333333333333,0;
    1,0,0];
s=scatter(x,y,sz, Color, 'filled');
colormap=(sort(Color, 'descend'));
set(gca, 'CLim', [1, 8]);
c=colorbar;

Results in the image below. The color bar axis/range is set, but I am trying to find a way to specify the face color of the color bar - away from the default - so that it only depicts the range of colors in the chart. Apologies in advance if this is a silly oversight!

Thank you again for your help.

Answer 1

[David Goodmanson]

Hi Carolyn, All you need do is change the colormap line to

colormap(sort(Color, 'descend'));

but make sure that you have cleared your variables first. With your previous command, Matlab creates a variable named 'colormap' and you do not want that.

The forgoing method works, but you get a pretty ugly colorbar with four sections of constant color. For a nicer colorbar you can make a more continuous version of the colormap, such as

x=[1,2,3,4];
y=[5,6,7,8];
sz = 100;
N = 64;   % or whatever
Color1 = [ones(N,1),(N-1:-1:0)'/(N-1),zeros(N,1)];
colormap(Color1)
s=scatter(x,y,sz,y,'filled');
colorbar

This also gives you the opportunity to put not a matrix of rgb values into the scatter 'C' input as you did, but but rather to make C a vector of the same length as x and y. Then the collection of C vector values is mapped into the entire colormap from bottom to top. As you see, the y values were mapped to colors in the code above. That idea may not apply directly in your case with the circular plot, but you can make a C vector with appropriate values that map into the colormap.

[Caroline Whyatt]

Hi David, thank you for noticing that oversight! The blending method that you kindly provided works very well - currently trying to adapt it to the circular plot. Many thanks!