Assign custom interval to the color map z axis of a surf plot

My surf (z) plot ranges from 0 to 255. i used turbo color map but the ranges per color were quite even across the value. i would like to able to set uneven custom interval for the colormap of my surf plot. I have checked through resources online, but could not figure it out for my case. Thanks in advance.

[KSSV]

Shjow us your expectatons with a pictorial example.

[OLUWAFEMI AKINMOLAYAN]

I don't have a pictorial sample of what I expect.. but the present colour bar i have is attached. the intervals were divided evenly to 255/7 (because there were 7 colours).

However, I want to be able to set a customed division of intervals for the colour map. For example, 0-20, 20-100, 100-155, 155-231, 231- 240, 240-250, 250-255.

[KSSV]

For what daya you want to use the colormap?

[OLUWAFEMI AKINMOLAYAN]

The data is quite larger than 5mb. i could not upload it. I just need an example. I can adapt it to my case

[OLUWAFEMI AKINMOLAYAN]

surf(peaks)
colormap turbo(7)
colorbar

The above is an example. However, I want to be able to use a custom interval. Instead of default range of even division of interval for the colors, I want a custom one.

Answer 1

[Mathieu NOE]

hello

try my little demo

the colorbar is "frozen" so that ticks / tickslabels do not vary acccording to data range. In other words , you can display data which max value can be either below or above the max value of the thresholds without graphical impact.

see the 2 examples shown below

hope it helps

Z = 5*abs(Z); % modify here the magnification factor to see effects on plot

Z = 50*abs(Z); % modify here the magnification factor to see effects on plot

[X,Y,Z] = peaks(50);
Z = 50*abs(Z); % modify here the magnification factor to see effects on plot

[maxval, ~] = max(Z(:));
[minval, ~] = min(Z(:));
maxval = ceil(maxval);
minval = floor(minval);

thresholds = [0 20 100 155 231 240 250 255]; % absolute thresholds for data ( 0-20, 20-100, 100-155, 155-231, 231- 240, 240-250, 250-255)
n_thr = numel(thresholds);

mycolormap = jet(n_thr); % NB : Z data can be higher than max value of thresholds
colormap(mycolormap); 

% create scaled color values C
    C = zeros(size(Z));
    for ck=1:n_thr-1
        C(Z >= thresholds(ck) & Z < thresholds(ck+1)) = ck;  % 
    end
    C(Z >thresholds(end)) = ck+1;  % do not forget data higher than max (last) value of thresholds

% plot
figure(1)
surf(X,Y,Z, C);
caxis([1 n_thr]); % freeze C axis (color) range
axis([-3 3 -3 3 0 maxval]);
cb_yticklabels = arrayfun(@num2str,thresholds,'uni',false);

cbh = colorbar;
set(cbh,'ytick',1+(n_thr-1)*(0:n_thr-1)/n_thr);
set(cbh,'yticklabel',cb_yticklabels);

[OLUWAFEMI AKINMOLAYAN]

Thanks @Mathieu NOE. However, I could not understand this. I am not looking to transform the "peaks" data to values ranging from 0 - 255. NO.

I only gave a sample plot. the values are from -6 to +8 wilh evenly divided interval. what if i interval i want is -6 to -5, -5 to -3.5, -3.5 to +0.5, +0.5 to +2.3, +2.3 to +4, +4 to +7.8, and +7.8 to 8. How do i go about it

[Mathieu NOE]

hello again

for my demo I simply followed your inputs :

My surf (z) plot ranges from 0 to 255.

and

I want to be able to set a customed division of intervals for the colour map. For example, 0-20, 20-100, 100-155, 155-231, 231- 240, 240-250, 250-255.

I f you want now to change the data range and / or the thresholds values in the colorbar that is something you can do in my code . The code by itself does not need any change

all the best

[Mathieu NOE]

hello

problem solved ?

[Mathieu NOE]

hello again

problem solved ?