Unable to create custom colormap from RGB data?

Question

0 votes

Still bogged down in the difference between an array and a matrix...

Everything was working well until I stumbled upon the following error message, at the time of attempting to create the colormap :

Colormap must be an Mx3 array of type single or double with values in the range [0,1] or an Mx3

array of type uint8.

Here's my code :

% Generate three vectors 
 Axe_A_B = transpose(linspace(-128, 128, 21));
 Axe_La = transpose(linspace(39, 50, 21));
 Axe_Lb = transpose(linspace(15,100, 21));
 
 Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_A_B]; % 21 x 3 double
 RGB_Axe_AB = lab2rgb(Lab_Axe_AB)
 
 % negatives values?
 [row,col] = size(RGB_Axe_AB);
 
 for ROW = 1:row     
     if RGB_Axe_AB(ROW,1) < 0
        RGB_Axe_AB(ROW,1) = 0;
     end
     if RGB_Axe_AB(ROW,2) < 0
        RGB_Axe_AB(ROW,2) = 0;
     end
     if RGB_Axe_AB(ROW,3) < 0
        RGB_Axe_AB(ROW,3) = 0;
     end
 end
 RGB_Axe_AB_ColorMap = colormap(RGB_Axe_AB)

I'm going in circle...

Documentation states :

% Colormap must have 3 columns: [R,G,B]

% defining a three-column matrix of values

Here's the content of my RGB_Axe_AB 'variable' :

RGB_Axe_AB =

0 0.5400 1.2184

0 0.5321 1.1330

0 0.5240 1.0486

0 0.5152 0.9653

0 0.5058 0.8831

0 0.4952 0.8020

0 0.4833 0.7220

0 0.4695 0.6432

0 0.4536 0.5654

0.2388 0.4349 0.4886

0.4126 0.4126 0.4126

0.5271 0.3857 0.3369

0.6198 0.3526 0.2607

0.7011 0.3106 0.1812

0.7756 0.2540 0.0886

0.8459 0.1660 0

0.9139 0 0

0.9810 0 0

1.0478 0 0

1.1142 0 0

1.1804 0 0

I did not bother to create a 256 size variable at this point. ...

0 Comments
Show -2 older comments Hide -2 older comments

Sign in to comment.

Sign in to answer this question.

Follow Question

Answer 1

Roger Breton on 18 Jan 2022

Edited: Walter Roberson on 18 Jan 2022

Open in MATLAB Online

0 votes

Oopsy, doopsy! I just realize there are values > 1.0 in those columns! Oh boy! Egg on my face...

Here's the revised code :

for ROW = 1:row     
     if RGB_Axe_AB(ROW,1) < 0
        RGB_Axe_AB(ROW,1) = 0;
     end
     if RGB_Axe_AB(ROW,1) > 1
        RGB_Axe_AB(ROW,1) = 1;
     end
     if RGB_Axe_AB(ROW,2) < 0
        RGB_Axe_AB(ROW,2) = 0;
     end
      if RGB_Axe_AB(ROW,2) > 1
        RGB_Axe_AB(ROW,2) = 1;
     end
     if RGB_Axe_AB(ROW,3) < 0
        RGB_Axe_AB(ROW,3) = 0;
     end
     if RGB_Axe_AB(ROW,3) > 1
        RGB_Axe_AB(ROW,3) = 1;
     end
 end

Naturally, everything works now. No more errors....

Is there a way to do this process more efficiently? Without resorting to a loop?

Thank you in advance for your help and patience :-)

6 Comments
Show 4 older comments Hide 4 older comments

Roger Breton on 18 Jan 2022

Edited: Walter Roberson on 18 Jan 2022

Open in MATLAB Online

Making progress... For those who are interested. The code is not elegant but it's the result I want. Right now, all I care to achieve is a colormap that goes from CIE Lab = 'the a* axis', from a* = -128 to a +127. This is my code :

% Generate three vectors 
 Axe_A_B = transpose(linspace(-128, 128, 21));
 Axe_La = transpose(linspace(39, 50, 21));
 Axe_Lb_Zero = transpose(linspace(0, 0, 21));
 
 Axe_Lb = transpose(linspace(15,100, 21));
 
 Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_Lb_Zero]; % 21 x 3 double
 RGB_Axe_AB = lab2rgb(Lab_Axe_AB)
 
 % negatives values?
 [row,col] = size(RGB_Axe_AB);
 
 for ROW = 1:row     
     if RGB_Axe_AB(ROW,1) < 0
        RGB_Axe_AB(ROW,1) = 0;
     end
     if RGB_Axe_AB(ROW,1) > 1
        RGB_Axe_AB(ROW,1) = 1;
     end
     if RGB_Axe_AB(ROW,2) < 0
        RGB_Axe_AB(ROW,2) = 0;
     end
      if RGB_Axe_AB(ROW,2) > 1
        RGB_Axe_AB(ROW,2) = 1;
     end
     if RGB_Axe_AB(ROW,3) < 0
        RGB_Axe_AB(ROW,3) = 0;
     end
     if RGB_Axe_AB(ROW,3) > 1
        RGB_Axe_AB(ROW,3) = 1;
     end
 end
 RGB_Axe_AB_ColorMap = colormap(RGB_Axe_AB)
 
 n=21
 colormap(RGB_Axe_AB_ColorMap(21))
 pcolor([1:n+1;1:n+1])
 

And this is the image -- what a beauty! :-)

Needless to say, there's still a ton of work to do. This is very encouraging. Thank you, Mr. Matlab :-)

I owe you a beer :-)

Roger Breton on 18 Jan 2022

Edited: Walter Roberson on 18 Jan 2022

Open in MATLAB Online

Making progress, using this code :

% Generate three vectors 
 Axe_A_B = transpose(linspace(-128, 128, 21));
 Axe_La = transpose(linspace(39, 50, 21));
 Axe_Lb_Zero = transpose(linspace(0, 0, 21));
 
 Axe_Lb = transpose(linspace(15,100, 21));
 
 Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_Lb_Zero]; % 21 x 3 double
 RGB_Axe_AB = lab2rgb(Lab_Axe_AB)
 
 % negatives values?
 [row,col] = size(RGB_Axe_AB);
 
 for ROW = 1:row     
     if RGB_Axe_AB(ROW,1) < 0
        RGB_Axe_AB(ROW,1) = 0;
     end
     if RGB_Axe_AB(ROW,1) > 1
        RGB_Axe_AB(ROW,1) = 1;
     end
     if RGB_Axe_AB(ROW,2) < 0
        RGB_Axe_AB(ROW,2) = 0;
     end
      if RGB_Axe_AB(ROW,2) > 1
        RGB_Axe_AB(ROW,2) = 1;
     end
     if RGB_Axe_AB(ROW,3) < 0
        RGB_Axe_AB(ROW,3) = 0;
     end
     if RGB_Axe_AB(ROW,3) > 1
        RGB_Axe_AB(ROW,3) = 1;
     end
 end
 RGB_Axe_AB_ColorMap = colormap(RGB_Axe_AB)
 Xcoord = linspace(-128, 128, 21);
 Ycoord = linspace(0, 0, 21);
 plot(Xcoord,Ycoord, 'LineWidth', 2, 'MarkerSize', 10);
 axis([-128 128 -128 128]);
 xticks([-128 -96 -64 -32 0 32 64 96 128]);
 yticks([-128 -96 -64 -32 0 32 64 96 128]);  
xs = linspace(-128, 128, 21);
hold on;
colorList = RGB_Axe_AB_ColorMap;
xAxisWidth = 10;
%  k = -128 : 6.0952 : 128
xRef=-128
for k = 1 : 21
    thisColor = colorList(k, :);
    line([xRef, xRef + 12.1905], [0, 0], 'Color', thisColor, 'LineWidth', xAxisWidth)
    xRef = xRef + 12.1905
end

And this is the result :

Almost feel like putting my feet up, now :-)

Thanks everyone for your kind and patient help!

Roger Breton on 18 Jan 2022

Is it ever complicated (read 'abstract') to work in 3D!

Got this encouraging result :

Using this humble code :

% Generate three vectors

Axe_A_B = transpose(linspace(-128, 128, 21));

Axe_La = transpose(linspace(39, 50, 21)); % Green to Magenta

Axe_Lb_Zero = transpose(linspace(0, 0, 21));

Axe_Lb = transpose(linspace(15,100, 21)); % Blue to Yellow

Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_Lb_Zero]; % 21 x 3 double

RGB_Axe_AB = lab2rgb(Lab_Axe_AB) % Green to Magenta

Lab_Axe_BA = [Axe_La, Axe_Lb_Zero, Axe_A_B]; % 21 x 3 double

RGB_Axe_BA = lab2rgb(Lab_Axe_BA) % Yellow to Blue

% negatives values?

[row,col] = size(RGB_Axe_AB);

% Process Green/Magenta axis first

for ROW = 1:row

if RGB_Axe_AB(ROW,1) < 0

RGB_Axe_AB(ROW,1) = 0;

end

if RGB_Axe_AB(ROW,1) > 1

RGB_Axe_AB(ROW,1) = 1;

end

if RGB_Axe_AB(ROW,2) < 0

RGB_Axe_AB(ROW,2) = 0;

end

if RGB_Axe_AB(ROW,2) > 1

RGB_Axe_AB(ROW,2) = 1;

end

if RGB_Axe_AB(ROW,3) < 0

RGB_Axe_AB(ROW,3) = 0;

end

if RGB_Axe_AB(ROW,3) > 1

RGB_Axe_AB(ROW,3) = 1;

end

[row,col] = size(RGB_Axe_BA);

% Process Yellow/Blue axis second

for ROW = 1:row

if RGB_Axe_BA(ROW,1) < 0

RGB_Axe_BA(ROW,1) = 0;

end

if RGB_Axe_BA(ROW,1) > 1

RGB_Axe_BA(ROW,1) = 1;

end

if RGB_Axe_BA(ROW,2) < 0

RGB_Axe_BA(ROW,2) = 0;

end

if RGB_Axe_BA(ROW,2) > 1

RGB_Axe_BA(ROW,2) = 1;

end

% fprintf('RGB_Axe_BA(ROW,3) Avant = %4.2f\n', RGB_Axe_BA(ROW,3))

if RGB_Axe_BA(ROW,3) < 0

RGB_Axe_BA(ROW,3) = 0;

end

if RGB_Axe_BA(ROW,3) > 1

RGB_Axe_BA(ROW,3) = 1;

end

% fprintf('RGB_Axe_BA(ROW,3) Après = %4.2f\n', RGB_Axe_BA(ROW,3))

end

RGB_Axe_AB_ColorMap = colormap(RGB_Axe_AB) % Green to Magenta colormap

RGB_Axe_BA_ColorMap = colormap(RGB_Axe_BA) % Yellow to Blue colormap

Xcoord = linspace(-128, 128, 21); % 1 x 21

Ycoord = linspace(0, 0, 21); % 1 x 21

Zcoord = linspace(0,100, 21);

Line3D = plot3(Xcoord,Ycoord, Zcoord); grid on; hold on;

set(Line3D, 'Visible', 'off');

xlabel('X axis a* (-128 +128)');

ylabel('Y axis b* (-128 +128)');

zlabel('Z axis L* (0 100)');

axis([-128 128 -128 128 0 100]);

xticks([-128 -96 -64 -32 0 32 64 96 128]);

yticks([-128 -96 -64 -32 0 32 64 96 128]);

zticks([0 10 20 30 40 50 60 70 80 90 100]);

% plot3(-128,-128, 0, 'o')

% plot3(-96,-128, 0, 'o')

xs = linspace(-128, 128, 21);

hold on;

colorListAB = RGB_Axe_AB_ColorMap; % Green to Magenta ColorList

colorListBA = RGB_Axe_BA_ColorMap; % Blue to Yellow ColorList

xAxisWidth = 5;

xRef=-128

yRef=-128

% line([-128, 128], [-128, -128], [0,0], 'Color', thisColor, 'LineWidth', xAxisWidth)

for k = 1 : 21

thisColor = colorListAB(k, :);

line([xRef, xRef + 12.1905], [yRef, yRef], [0, 0], 'Color', thisColor, 'LineWidth', xAxisWidth)

xRef = xRef + 12.1905

end

% plot3(-128,128, 0, 'o')

% plot3(-128,96, 0, 'o')

% line([-128, -128], [128, 96], [0,0], 'Color', thisColor, 'LineWidth', xAxisWidth)

xRef=-128

yRef=128

for k = 1 : 21

thisColor = colorListBA(k, :);

line([xRef, xRef], [yRef, yRef - 12.1905], [0, 0], 'Color', thisColor, 'LineWidth', xAxisWidth)

yRef = yRef - 12.1905

end

I had to resort to plotting individual points in order to visualize the required coordinates.

There are still points which puzzles me but I know I'm in the right direction.

Thank you all for your help and patience.

Roger Breton on 18 Jan 2022

"One more thing" as Steve Jobs used to say... My axes were "reversed"? So, I thought I was going to crawl under untangling the correct logic but I only changed a few lines and here is the correct result :

I had to change these lines of code :

% Generate three vectors

Axe_A_B = transpose(linspace(-128, 128, 21));

Axe_B_A = transpose(linspace(128, -128, 21));

Axe_La = transpose(linspace(39, 50, 21)); % Green to Magenta

Axe_Lb_Zero = transpose(linspace(0, 0, 21));

Axe_Lb = transpose(linspace(15,100, 21)); % Blue to Yellow

Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_Lb_Zero]; % 21 x 3 double

RGB_Axe_AB = lab2rgb(Lab_Axe_AB) % Green to Magenta

Lab_Axe_BA = [Axe_La, Axe_Lb_Zero, Axe_B_A]; % 21 x 3 double

RGB_Axe_BA = lab2rgb(Lab_Axe_BA) % Yellow to Blue

Still many, many, many details to work on but, I'm so please with this result, so far.

Roger Breton on 18 Jan 2022

Rome was not built in one day... I spotted an error in the appearance of yellow? This is the corrected code :

% Generate three vectors

Axe_A_B = transpose(linspace(-128, 128, 21));

Axe_B_A = transpose(linspace(-128, 128, 21));

Axe_La = transpose(linspace(39, 50, 21)); % Green to Magenta

Axe_Lb_Zero = transpose(linspace(0, 0, 21));

Axe_Lb = transpose(linspace(15,100, 21)); % Blue to Yellow

Lab_Axe_AB = [Axe_La, Axe_A_B, Axe_Lb_Zero]; % 21 x 3 double

RGB_Axe_AB = lab2rgb(Lab_Axe_AB) % Green to Magenta

Lab_Axe_BA = [Axe_Lb, Axe_Lb_Zero, Axe_B_A]; % 21 x 3 double

Flipped = flipud(Lab_Axe_BA);

% RGB_Axe_BA = lab2rgb(Lab_Axe_BA) % Yellow to Blue

RGB_Axe_BA = lab2rgb(Flipped) % Yellow to Blue

Had to flip the array upside down, to get the correct Lab (RGB) values to appear at the correct (b* = +128) end of the scale. Silly me. Now this is better :

Sign in to comment.

Unable to create custom colormap from RGB data?

0 Comments
Show -2 older comments Hide -2 older comments

Accepted Answer

6 Comments
Show 4 older comments Hide 4 older comments

More Answers (0)

Categories

Products

Release

Tags

Community Treasure Hunt

Unable to create custom colormap from RGB data?

0 Comments Show -2 older comments Hide -2 older comments

Accepted Answer

6 Comments Show 4 older comments Hide 4 older comments

More Answers (0)

Categories

Products

Release

Tags

See Also

Community Treasure Hunt

0 Comments
Show -2 older comments Hide -2 older comments

6 Comments
Show 4 older comments Hide 4 older comments