Question

I load images in matlab and work with them as double matrices.

Now I want to extract the data values across a straight line from one point of the image to another. This line however does not equal to a column or row (that would be easy).

How can I do that with matlab?

Answer 1

A line obeys the eq of the line y=a*x+b. Here x and y are coordiantes of the image. So if you want a line defined by two points (x1,y1) -> (x2,y2), the slope a is (y2-y1)/(x2-x1) and b=y1-a*x1. So next , select points in the matrix the obey the eq of the line as follows:

Create data and end points:

m=peaks(50);
x1=5 ; x2=42;
y1=21; y2=29;

calculate ew of line parameters:

a=(y2-y1)/(x2-x1);
b=y1-a*x1;

define the line:

x=x1:x2;
y=round(a*x+b);

select the proper matrix elements using linear indexing:

ind=sub2ind(size(m),y,x)

plot:

subplot(2,1,1)
imagesc(m); hold on
colormap(bone)
line([x1 x2],[y1 y2],'Color',[1 0 0]);

subplot(2,1,2)
plot(m(ind))