Create an RGB image from an elevation array.

I need to rite a script to read the elevation data set. Then create an RGB image the same size as the elevation array. Then color all points above sea level (elev > 0) black, and color all points below sea level blue.

Answer 1

[KALYAN ACHARJYA]

Lets suppose 'data' is the the elevation data set

data= randi([-5,5],[50,50]); % Example
%....................^the array may have any dimention
% Fore all data>0 to 0, which result black pixels
data(data>=0)=0;
% Make all data<0 to blue pixel Blue=[R=0,G=0,B=139]
% Create three Plane for RGB 
R=data;G=data;B=data;
R(data<0)=0; G(data<0)=0; B(data<0)=139;
rgbImage=cat(3,R,G,B);
figure,imshow(rgbImage,[]);

Answer 2

[Image Analyst]

If you want to use a colormap instead of an RGB image like KALYAN showed you, you can do this, though I admit it's tricker/harder than the RGB version:

% Create sample data between -500 and +2000 meters.
seaDepths = -500 + 2000 * rand(40, 60);

% Create colormaps.  Choose one of the two options below and command the other one out.
% Option 1 : Create colormap with pure 100% solid blue everywhere 
% except on one row that will be used to color map for data > 0
cmap = [zeros(256,1), zeros(256,1), ones(256, 1)]
cmap(end,:) = 0; % Black.
% Option 2 : Create colormap with a gradient from blue at -500 to black at 0
cmap = [zeros(256,1), zeros(256,1), (255:-1:0)'] / 255

% Display the image with the colormap we created.
imshow(seaDepths, [], 'ColorMap', cmap);
axis('on', 'image');
caxis([-500, 0]);
colorbar
impixelinfo; % Let user mouse around and see the original depth value.
% Maximize figure window.
g = gcf;
g.WindowState = 'maximized';