Convert pixel into Coordinate

Hello All,

I have an image of a material made by 3 different components. For each component I assigned a colour. I have attached the 2 photos.

I would like to convert the pixels into coordinate assigning the type and defining also the scale of axis.

As the final result I would like to obtain these informations:

x and y lenght

N# pixel x y type

1 0.01 0.01 1

2 0.02 0.01 1

3 0.03 0.01 2

4

...

I have already did something similar for a binary images but not with and rgb

Many thanks

Answer 1

[Kiran Felix Robert]

Hi Danilo Sanfilippo,

I understand that you have a RGB image with three colours each corresponding to a different material. You attempt to determine which pixel correspond to which type, viz. 1,2,3 and to get the coordinate by using an appropriate scaling value from the pixel locations.

The image segmentation using k-means function can be used to map each pixel value to the type of material (Assuming each colour as a cluster, here you can use it to be 3 clusters as you need 3 different materials). (imsegkmeans)

pixelsType = imsegkmeans(image,3,'NumAttempts',4); 

The output of imsegkmeans function, say pixelsType, is a 2D matrix which is same as the size of the image, with the type number of each pixel corresponding to the Matrix Element. The pixelsType matrix can be directly used to get the coordinate value using the appropriate scaling factor as shown below,

nr = size(pixelType,1); % Number of Rows 
nc = size(pixelType,2); % Number of Columns 
N = 1:nr*nc; % Pixels Number Vector 
kx = 0.5; %x - scaling Factor; 
ky = 0.5; %y - scaling Factor; 
x = zeros(nc*nr,1); %pre-allocating the x-coordinates 
y = zeros(nc*nr,1); %pre-allocating the y-coordinates 
type = zeros(nc*nr,1); %pre-allocating the type 
i = 1; 
for r = 1:nr 
    for c = 1:nc 
        x(i) = r*kx;  
        y(i) = c*ky; 
        type(i) = pixelsType(r,c); 
        i = i + 1; 
    end 
end 
A = [N' x y type]; % matrix A contains the required values 
csvwrite('Req.csv',A) %Write the matrix A into a csv file 

Kiran Felix Robert