Discrete color scale in 3D plot

The following code produces a strip in the middle of a flat base. How can I adjust the color bar so that I can use only one color to represent the data range [0 2), one color for (2 4], one color for (4 6], and so on? So the color on the strip will be discrete on each level, rather than a continuous transition.

img = zeros(101,101);
img(51,51) = 10;

% let's try discrete color scale
surf(img)
shading interp
colorbar
axis tight

Answer 1

[Image Analyst]

Try this:

clc;
close all;
img = zeros(101,101);
img(51,51) = 10;

% let's try discrete color scale
surf(img)
shading interp
axis tight
myCustomColorMap = zeros(256, 3);
% Map 0-2, which is the first 20% or 51 elements:
row1 = 2;
row2 = row1 + 50;
myCustomColorMap(row1:row2,:) = repmat([1,0,0], [row2-row1+1, 1]); % Red
% Map 2-4, which is the next 20% or 51 elements:
row1 = row2+1;
row2 = row1 + 50;
myCustomColorMap(row1:row2,:) = repmat([0,1,0], [row2-row1+1, 1]); % Green
% Map 4-6, which is the first 20% or 51 elements:
row1 = row2+1;
row2 = row1 + 50;
myCustomColorMap(row1:row2,:) = repmat([0,0, 1], [row2-row1+1, 1]); % Blue
% Map 6-8, which is the first 20% or 51 elements:
row1 = row2+1;
row2 = row1 + 50;
myCustomColorMap(row1:row2,:) = repmat([1,1,0], [row2-row1+1, 1]); % Yellow
% Map 8-10, which is the first 20% or 51 elements:
row1 = row2+1;
row2 = size(myCustomColorMap, 1);
myCustomColorMap(row1:row2,:) = repmat([1,0,1], [row2-row1+1, 1]); % Magenta
colormap(myCustomColorMap);
colorbar

[Kyle Wang]

Actually, I have some extra concerns about the colorbar.

img = zeros(101,101);
img(51,51) = 10;
% let's try discrete color scale
surf(img)
shading interp
axis tight
zlim([0 20])

Now I'm trying to create a colorbar with 4 scales: 0-5, 5-10, 10-15, 15-20. So the mid strip should have only two colors. Is it possible to do this?

[Image Analyst]

Sure. Just understand the code. The color map has 256 rows and 3 columns. Column 1 is the red value and is in the range 0-1. Column2 is green, and column 3 is the blue value. So that 256 rows spans your range of your data - 0 to 10 in your case. So just figure out what row corresponds to what value and set the color for that row. Does that explain it better?

[Kyle Wang]

umumum, I understand somehow the color rules in matlab, still something wrong in my code. The strip has three colors instead of two. and the color ticks do not align with the color level?

img = zeros(101,101);
img(51,51) = 10;
% let's try discrete color scale
surf(img)
shading interp
axis tight
zlim([0 20])

colorLevel = 5;
colorMapSize = colorLevel * 50 + (colorLevel + 1);
myCustomColorMap = zeros(colorMapSize, 3);
grayColor = jet(colorLevel+1); % 1st = [0 0 0]

row1 = 2;
row2 = row1 + 50;
myCustomColorMap(row1:row2,:) = repmat(grayColor(2,:), [row2-row1+1, 1]);

for n = 2: colorLevel
    row1 = row2+1;
    row2 = row1 + 50;
    myCustomColorMap(row1:row2,:) = repmat(grayColor(n+1,:), [row2-row1+1, 1]);
end

colormap(myCustomColorMap);
caxis([0 20])

hcb = colorbar;
set(hcb,'YTick',[0 5 10 15 20 25]);

[Kyle Wang]

The line

grayColor = jet(colorLevel+1); % 1st = [0 0 0]

can also be

grayColor = gray(colorLevel+1); % 1st = [0 0 0]

[Kyle Wang]

oops, just made the following change then the colorbar works fine:

colorLevel = 4;