Try this. First we figure out what the colormap looks like using the sample image. Then we know how to build it and we can use linspace(), ones(), and zeros() to build a perfect one that we can apply to any image.
% Let see what this map looks like by examining the sample image.
hFig = figure;
fontSize = 20;
rgbImage = imread('image.png');
subplot(3, 1, 1);
imshow(rgbImage);
axis('on', 'image');
impixelinfo
redMap = rgbImage(18:122, 280, 1);
greenMap = rgbImage(18:122, 280, 2);
blueMap = rgbImage(18:122, 280, 3);
plot(redMap, 'r-', 'LineWidth', 2);
hold on;
plot(greenMap, 'g-', 'LineWidth', 2);
plot(blueMap, 'b-', 'LineWidth', 2);
legend('Red', 'Green', 'Blue', 'Location', 'southeast');
grid on;
title('Colormap from Sample image', 'FontSize', fontSize);
% Synthesize a similar "perfect" colormap.
% You don't need the sample image anymore - that was just to figure out how we could build this colormap.
numColors = 64; % An even number!
c4 = numColors/4;
redMap = [linspace(125, 255, c4), 255 * ones(1, c4), linspace(255, 0, c4), zeros(1, c4)] / 255;
greenMap = [zeros(1, c4), linspace(0, 255, c4), linspace(255, 0, c4), zeros(1, c4)] / 255;
blueMap = fliplr(redMap);
cMap = [redMap(:), greenMap(:), blueMap(:)];
subplot(3, 1, 2);
plot(redMap, 'r-', 'LineWidth', 2);
hold on;
plot(greenMap, 'g-', 'LineWidth', 2);
plot(blueMap, 'b-', 'LineWidth', 2);
legend('Red', 'Green', 'Blue', 'Location', 'southeast');
grid on;
title('Regenerated Colormap', 'FontSize', fontSize);
% Read in a gray scale image that we can apply the colormap to.
grayImage = imread('cameraman.tif');
subplot(3, 1, 3);
imshow(grayImage);
axis('on', 'image');
impixelinfo
title('Regenerated Colormap', 'FontSize', fontSize);
% Apply it to the image.
colormap(cMap);
colorbar;
hFig.WindowState = 'maximized';
fprintf('Done running %s.m.\n', mfilename);
