create specific color map and save it

how do i create my own color map for 2D-scatter plot.

such that all the values of z

1. z <= 10 ------- take green color
2. 10 < z <= 25 ----- yellow color
3. 25 < z <= 50 ----- orange color
4. z > 50 ----- red color

i want to create a color map obeying such condition and save it , so that i can use with whatever z i obtain in future.

as an example i have attached x,y,z

scatter(x,y,[],z,'filled','o')

[KSSV]

Same question you have asked multiple times...

Answer 1

[Ameer Hamza]

Try this

val_z = (10:51).';
idx = 1*(val_z<=10) + ...
    2*((10<val_z) & (val_z<=25)) + ...
    3*((25<val_z) & (val_z<=50)) + ...
    4*(val_z>50);
colors = [0 1 0; % green
          1 1 0; % yellow
          1 0.5 0; % orange
          1 0 0]; % red
cmap = colors(idx, :);

scatter(x,y,[],z,'filled','o')
colormap(cmap)
set(gca, 'CLim', [10 51]);

[Sajid Afaque]

as i am new to this concept,can you please explain me the above code.

[Ameer Hamza]

This uses basic indexing operations available in MATLAB. It is difficult to summarize everything in one comment. I suggest running this code line by line and see the output of each step. Also, read about the indexing from the following links

https://www.mathworks.com/help/matlab/math/array-indexing.html

https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

https://www.mathworks.com/help/matlab/learn_matlab/array-indexing.html

[Sajid Afaque]

First of al thank you for your help.

i am getting the colors according to my conditions.

but my color bar is showing up weird.

why is orange color repeating itself to the position of its value. and why don't green and yellow show up in color bar.

Additionally ,what should to i do to have increase in the darkness of color as value increases.( for example value > 50 we have red color, how can we acheive such that 51 has light red compared to 55 which should again be light red compared 60 and so on, my max value should be dark red)

[Ameer Hamza]

Try this

val_z = (10:max(z)).';

cmap = zeros(numel(val_z), 3);
mask = val_z<=10;
cmap(mask, :) = repmat([0 1 0], sum(mask), 1); % green
mask = (10<val_z) & (val_z<=25);
cmap(mask, :) = repmat([1 1 0], sum(mask), 1); % yellow
mask = (25<val_z) & (val_z<=50);
cmap(mask, :) = repmat([1 0.5 0], sum(mask), 1); % orange

mask = val_z>50;
n = sum(mask);
t = linspace(0, 1, n).';
red = [1 0 0];
dark_red = [0.3 0 0];
cmap(mask, :) = (1-t).*red + t.*dark_red;

scatter(x,y,[],z,'filled','o')
set(gca, 'CLim', [10 max(z)]);
colormap(cmap)
colorbar

[Sajid Afaque]

I am getting this error

[Ameer Hamza]

Which MATLAB version are you using?

[Sajid Afaque]

2013b

[Ameer Hamza]

You can try this

val_z = (10:max(z)).';

cmap = zeros(numel(val_z), 3);
mask = val_z<=10;
cmap(mask, :) = repmat([0 1 0], sum(mask), 1); % green
mask = (10<val_z) & (val_z<=25);
cmap(mask, :) = repmat([1 1 0], sum(mask), 1); % yellow
mask = (25<val_z) & (val_z<=50);
cmap(mask, :) = repmat([1 0.5 0], sum(mask), 1); % orange

mask = val_z>50;
n = sum(mask);
t = linspace(0, 1, n).';
red = [1 0 0];
dark_red = [0.3 0 0];
cmap(mask, :) = interp1([0 1], [red; dark_red], t);

scatter(x,y,[],z,'filled','o')
set(gca, 'CLim', [10 max(z)]);
colormap(cmap)
colorbar

[Sajid Afaque]

again my colorbar shows green at higher values whereas it should have been limited to trange 0-10

[Ameer Hamza]

There seems to be some difference in the working of colormap in R2013b. In R2020a, it looks fine

[Sajid Afaque]

yeah color ranges are ok ,only colorbar gets repeated after certain interval.

do you have any idea why this may be.

thank you for your help .

much appreciated

[Ameer Hamza]

I don't have any idea about this. Maybe something is mentioned in archived documentation, but the reason is not obvious.