CODEWITHSUNDEEP
matlabimage-processingcomputer-visionrgbpixel
Nasser Taha
Nasser Taha

Reputation: 23

get pixel coordination by rgb values matlab

how can I get the x,y coordinates for pixels in an image by rgb values in matlab ?

for example : I've got an image that I want to locate the pixels coordinates od the black area in it..

Upvotes: 2

Views: 775

Answers (2)

Tommaso Belluzzo
Tommaso Belluzzo

Reputation: 23685

There is a built-in function that does this: impixel. From the official documentation:

Return Individual Pixel Values from Image

% read a truecolor image into the workspace
RGB = imread('myimg.png');

% determine the column c and row r indices of the pixels to extract
c = [1 12 146 410];
r = [1 104 156 129];

% return the data at the selected pixel locations
pixels = impixel(RGB,c,r)

% result
pixels = 
    62    29    64
    62    34    63
   166    54    60
    59    28    47

Link: https://it.mathworks.com/help/images/ref/impixel.html

[EDIT]

Ok, I misunderstood your question. So to accomplish what you are looking for just use the following code:

img = imread('myimg.png');

r = img(:,:,1) == uint8(0);
g = img(:,:,2) == uint8(0);
b = img(:,:,3) == uint8(255);
[rows_idx,cols_idx] = find(r & g & b);

The example above finds all the pure blue pixels inside the image (#0000FF) and returns their indices. You can also avoid casting values to uint8, it should work anyway by implicitly converting values during comparison.

Upvotes: 0

Shai
Shai

Reputation: 114866

If you want to find all coordinates of pixles with values (R, G, B) then

[y, x] = find(img(:,:,1)==R & img(:,:,2)==G & img(:,:,3)==B);

For black pixels choose R=0, G=0, B=0

Upvotes: 2

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