Intensity of each pixel frawn on an image

I want to find out the intensity of every pixel if i draw a line on one image.

Im using the below code for drawing a line. Initial valu of (xi,yi) = (353,216) and the final value is (xf,yf) = (553,216).

I = imread('figure63.png');
figure, imshow(I)
hold on
p1 = [353,216];
p2 = [553,216];
plot([p1(1),p2(1)],[p1(2),p2(2)],'Color','m','LineWidth',1)

If I want intensity of every pixel of this line as a column matrix, how do I use imaprofile or I need to use something else?

Answer 1

[KSSV]

Read about interp2. You can use interp2 for this.

I = imread('figure63.png');
[m,n,p] = size(I) ; 
[X,Y] = meshgrid(1:n,1:m) ; 

% Line points 
p1 = [353,216];
p2 = [553,216];
% Form a line using polyfit 
p = polyfit([p1(1);p2(1)],[p1(2);p2(2)],1) ; 
x = linspace(p1(1),p2(1)) ;
y = polyval(p,x) ; 
% 
iwant = zeros(length(x),p) ;  
% Assuming image to RGB 
for i = 1:p
    iwant(:,i) = interp2(X,Y,I(:,:,i),x,y)
end
end
figure, imshow(I)
hold on
plot(x,y,'Color','m','LineWidth',1)

[U B]

There's an error coming up.

Error using polyfit (line 44)

The first two inputs must have the same number of elements.

Error in intensity_of_a_line (line 8)

p = polyfit([p1;p2],1) ;

[KSSV]

It is problem with inputs to polyfit, you need to input like shown:

p = polyfit([p1(1);p2(1)],[p1(2);p2(2)],1) ;

Edited the code too.

[U B]

got it.

Answer 2

[Walter Roberson]

I(p1(2), p1(1):p2(1))

except you should use min and max to ensure that you get increasing order for the column numbers.

This depends on the y coordinates being the same and being integers, a horizontal line. You could use similar logic for a vertical line.

If you need a slanted line then you need improfile or go directly for interp2 which is what improfile uses internally.

[U B]

Yes. This one works. Thank you so much.