Extracting blue objects of interest

Hi,

I have an image of a circuit board with very blue chips. I want to display the blue chips as blue and display the rest of the board in greyscale.

My approach so far is:

image = imread('board.tif');

redBand = image(:,:,1); greenBand = image(:,:,2); blueBand = image(:,:,3);

After this I want to get everything in greyscale but display the blue chips on the same image. I think I have to put a red and green mask but I'm unsure how to do this. Any insights?

Answer 1

[Christiaan]

Dear Izuru,

I made a code for you, where first the color 'blue' is detected at a certain threshold. (here 200) Then with a for loop, all points where the color is below the threshold are neglected. The image I used has been put in the attachment.

   clc; clear all; close all;

% Read standard MATLAB demo image.
rgbImage = imread('board.jpg');

% Display the original image.
subplot(1, 3, 1);
imshow(rgbImage);
title('Original RGB Image');
% Maximize figure.
set(gcf, 'Position', get(0, 'ScreenSize'));

% Split into color bands.
redBand = rgbImage(:,:, 1);
greenBand = rgbImage(:,:, 2);
blueBand = rgbImage(:,:, 3);

% Display them.
subplot(1, 3, 2);
imshow(blueBand);
title('Blue Band');

% here objects which are parly blue make totaly blue
for i=1:152
    for j=1:229
        if blueBand(i,j)>200
            redBand(i,j)=0.1;
            greenBand(i,j)=0.1;
            blueBand(i,j)=200;
        end
    end
end

% here objects which are not blue to dark
for i=1:152
    for j=1:229
        if blueBand(i,j)<200
            redBand(i,j)=redBand(i,j)*0.2;
            greenBand(i,j)=greenBand(i,j)*0.2;
            blueBand(i,j)=blueBand(i,j)*0.2;
        end
    end
end

% Display them.
subplot(1, 3, 3);
im = cat(3,redBand,greenBand,blueBand);
imshow(im);
title('Blue Objects');

A second possibility would be using a tool from the File Exchange. A nice feature is 'imoverlay'. If you call this tool by writing in the prompt : >>imoverlay_tool and then use as a background 'blueband' (0-255), in the foreground'blueband' (200-250) and in the overlay (alpha 0.8) you obtain a figure that is blue where the objects are blue and the rest is gray.

Good luck! Christiaan

Answer 2

[Image Analyst]

You can use my demos that find specified colors. Try the delta E one, or the one that does it in HSV color space.

http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

 Change the thresholds in the HSV one to get blue instead of yellow.  For the delta E demo, you don't need to do that because you give it an example of the color you want to find by tracing a small region.

[Image Analyst]

Attach your image if you need more help.