How to create an RGB image?

What I have done thus far to create RGB images is to just load a white image and seperate the red green and blue components from this image and combine them in different ways to get different colors. No this feels kind of redundant because I keep thinking that MatLab must have a built-in RGB system in which you can just write a one line code from which the output will be any of the colors within RGB. Is there a simple function for this?

[Walter Roberson]

I am not clear as to what the desired inputs would be, or the desired outputs?

Answer 1

[MathReallyWorks]

Hello,

As far as I know, there is no direct function to do this. But if you want you can create a user defined function to randomly select any of the colors within RGB.

If you want to create RGB image from some kind of matrix, try this:

 image=zeros(300,400,3); %initialize
 image(:,1:100,1)=0.5;   %Red (dark red)
 image(:,101:200,1)=1;   %Red (maximum value)
 image(1:100,:,2)=rand(100,400);  %Green
 figure, imshow(image)

source: Michael Haderlein's Answer

Answer 2

[Jan]

No, there is no such command. Accessing the channels is so easy, that it is not worth to create a dedicated function:

RGB  = rand(64, 48, 3);  % RGB Image
R    = RGB(:, :, 1);
G    = RGB(:, :, 2);
B    = RGB(:, :, 3);
IMG1 = cat(3, G, R, B);

Now the channels swapped.

[Zeff020]

Ok, thanks! this is basically what I did. The problem that I had with this though is that you can only create the primary colors RGB and (when you combine these) their secondary colors: Yellow, Magenta and Turquoise. Now I would like to be able to create every color on the spectrum, is there no function to do this?

[Jan]

Do you mean:

IMG1 = cat(3, 0.8*G + 0.2*R, 0.3*R + 0.7*B, 0.1*B + 0.2*G + 0.7*R);

Of course you can get the full RGB spektrum.

What exactly is the problem you want to solve? Which color should be produced based on which input?

[Walter Roberson]

Looking at https://www.mathworks.com/matlabcentral/answers/342073-is-there-a-color-database-existent perhaps the request is for the ability to input a color name and get an rgb value out.

Or perhaps the request is just for something like

swath = @(r,g,b,rows,cols) = cat(3, r * ones(rows, cols), g * ones(rows, cols), b * ones(rows, cols) )

or equivalently

swath = @(r,g,b,rows,cols) = repmat( cat(3,r,g,b), rows, cols, 1)

Either of these would produce a rows x cols matrix of solid color with components r, g, and b.

Answer 3

[Tariq Hussain]

r=zeros(400);
g=r;
b=r;
r(1:200,1:200)=255;
g(1:200,201:end)=255;
b(201:400,1:200)=255;
r(201:end,201:end)=255;
rgbimg=cat(3,r,g,b);
figure,imshow(rgbimg)

Answer 4

[DGM]

If all you're after is a uniform colored field, it can be rather simple. You don't have to get stuck trying to intuit your way away from primary-secondary color schemes by channel filling/deletion. Just pick any arbitrary color tuple and replicate it.

% uniform color fields with class specification
s0 = [50 50]; % output image size

% uint8
cp1 = repmat(permute(uint8([57 177 242]),[1 3 2]),s0);
% same thing, but double
cp2 = repmat(permute([57 177 242]/255,[1 3 2]),s0);

Maybe you're not sure how to select the color tuple you want without seeing it. There are system-level and web-based color pickers that you could use. There are plenty on the File Exchange. MIMT has cpicktool() (HSL/LAB picker) and colorpicker() (sample colors from an image). Stephen has some excellent tools that may be of use.

Of course, it's not terribly clear if a solid color is what you're after. If you're trying to colorize an image, this might be useful:

How do i convert grayscale to rgb?

Otherwise, there might be other options in this thread:

How to create RGB image in MATLAB?