How image re-sized using bilinear interpolation?

Answer 1

In bi-linear there is the syllable 'bi'.

An image has two axis and basically we do a linear interpolation for each axis.

Suppose that my original image has pixels with intensity values a,b,c and d arranged like this:

a b

c d

I would like to determine the value for a pixel e positioned somewhere in this square.

a b

e

c d

Suppose that e is at a horizontal distance X from a and c. (X being a number between 0 and 1.

I do a first linear interpollation on the horizontal axis to find f and g with f and g at the same distance from the left:

f

e

g

Therefore:

f = a+(b-a).X;

g = c+(d-c).X;

f,e and g are on the same vertical line.

Now we suppose that the distance from e to f is Y (Y being between 0 and 1).

We do the vertical linear interpolation and find the result:

e=f+(g-f).Y;

We do this for every pixel 'e' in the output image and we find the resulting image.