Spectral lightness rainbow

Quick post to share my replica of Ethan Montag ‘s Spectral lightness colormap from this paper. My version has a linear Lightness profile (Figure 1) that increases monotonically from 0 (black) to 100 (white) while Hue cycles from 180 to 360 degrees and then wraps around and continues from 0 to 270.

You can download the colormap files (comma separated in MS Word .doc format) with RGB values in 0-1 range and 0-255 range.

Figure 1

Figure 2

Matlab code

To run this code you will need Colorspace, a free function from Matlab File Exchange, for the color space transformations.

%% generate Chroma, Lightness, Hue components
h2=linspace(0,270,60*2.56);
h1=linspace(180,360,103);
h=horzcat(h1,h2);
c=ones(1,256)*25;
l=linspace(0,100,256);

%% merge together
lch = vertcat(l,c,h)';

%% convert to RGB
rgb = colorspace('LCH->rgb',lch);

%% Plot color-coded lightness profile
figure;
h=colormapline(1:1:256,lch(:,1),[],rgb);
set(h,'linewidth',2.8);
title('Montag Spectral L* lightness plot ','Color','k','FontSize',12,'FontWeight','demi');

%%  Pyramid test data
PY=zeros(241,241);
for i = 1:241
    temp=(0:1:i-1);
      PY(i,1:i)=temp(:);
end
test=PY.';
test=test-1;
test(test==-1)=0;
test1=test([2:1:end,1],:);
PY1=PY+test1;
PY2=fliplr(PY1);
PY3= flipud(PY1);
PY4=fliplr(PY3);
GIZA=[PY1,PY2;PY3,PY4].*2;
x=linspace(1,756,size(GIZA,1));
y=x;
[X,Y]=meshgrid(x,y);
clear i test test1 PY PY1 PY2 PY3 PY4 temp;

%% display Pyramid surface
fig1=figure;
surf(X,Y,GIZA,GIZA,'FaceColor','interp','EdgeColor','none');
view(-35,70);
colormap(rgb);
axis off;
grid off;
colorbar;
% set(fig1,'Position',[720 400 950 708]);
% set(fig1,'OuterPosition',[716 396 958 790]);
title('Montag Spectral L*','Color','k','FontSize',12,'FontWeight','demi');

Aknowledgements

The coloured lightness profiles were made using the Colormapline submission from the Matlab File Exchange.