RGB colour pixel plot

Hello,

I am fairly new to matlab and was wondering if there is a way to create a plot with three axis on for each red green and blue which plots the values of RGB for each pixel in an image. I have the image processing toolbox but cannot work out how to do this.

Thanks for any help

Olly

Answer 1

[Image Analyst]

You could use scatter3, like I did, to produce somewhat lame 3D color scatterplots. But you're far, far better off using ImageJ ( http://rsb.info.nih.gov/ij/ ) and the color gamut inspection plugin ( http://rsb.info.nih.gov/ij/plugins/color-inspector.html ). At least until MATLAB puts in a similar capability. You can get this plug-in to work in MATLAB if you make a shortcut on your toolbar and follow these directions and put in this code:

% Windows installation instructions:
% First, download and install ImageJ from here:
% http://rsb.info.nih.gov/ij/download.html
% Then download the 3D Color Inspector plug-in for ImageJ here:
% http://rsb.info.nih.gov/ij/plugins/color-inspector.html
% and save it here:
% C:/Program Files/ImageJ/plugins/Color
%
% Now we need to enable the plug-in to work with MATLAB.
% First open your classpath file:
% C:\Program Files\MATLAB\R2011a\toolbox\local\classpath.txt
% for editing.  Then add the following lines as new lines to your classpath file:
% C:/Program Files/ImageJ/ij.jar
% C:/Program Files/ImageJ/plugins/Color/Color_Inspector_3D.jar

clc;  % Clear the MATLAB command window.
% User must browse for the file they want to open.
% Set up a starting/initial folder that they will start browsing from.
startingFolder = pwd; % Change to something specific if you want.
if ~exist(startingFolder, 'dir')
        startingFolder = pwd;
end
% Bring up the "Open File" dialog box.
[baseFileName, folder] = uigetfile({'*.jpg;*.tif;*.png;*.gif;*.bmp','Image Files (jpg,tif,png,bmp,gif)';...
'*.*','All Files (*.*)' },'Specify image file', startingFolder);

if baseFileName ~= 0
        % If they didn't click Cancel, build the full filename:
        fullFileName = fullfile(folder, baseFileName)
        % Now pass that into the 3D Color Inspector plugin, and you're done.
        color_inspector(fullFileName)
end

Then simply click your toolbar button and you'll have an excellent color gamut inspector without having to reinvent it yourself.

Answer 2

[Nerea Zubiaurre]

Image Analyst, I have a question regarding this. I am working on a project where I first select some colors by clicking the image (I am not using any specific color space for the moment as I am trying many to check which one works best for me), then I create a convex hull and finally I check every pixel in the image to get to know if they correspond to the range of colors I am looking for. The project is about skin lesions and it seems this algorithm is not very effective. Do you think I could do something with the gamuts?

[Image Analyst]

You definitely need to get that imageJ plug-in to visualize your gamut. Then you will see which color space would be best for segmenting your images. Getting the convex hull of the colors you clicked on is a start but you are probably missing some colors unless you click some "borderline" pixel colors. Even then it's possible your gamut may not be something that is best captured with a convex hull. Skin for example has a banana or boomerang shaped gamut if you consider the gamut of all races (skin colors).

[Nerea Zubiaurre]

Thank you Image Analyst. And where can I get the imageJ plug-in???

[Image Analyst]

Read the comments in the code above. It's in the first few lines.

Answer 3

[Nerea Zubiaurre]

Thanks! :)