How can I set the center of scaling?

Question

I'm working in some graphics programming in java. At the moment I can scale a picture image what I store in a 1D array. (it store row by row)

My code like where is the new position? newpoz = (int)(x * scale) + (int)(y * scale) * width;

This gives me a position in the array. But it scaling by the 0,0 coordinate what is in the top left corner. How can I set it to the center if the screen? So to the screen.getWidth()/2;screen.getHeight()/2.

Demonstration

Somebody can help with this? If there is any question I will answer in the comments.

Answer 1

To scale pixel coordinates about some center (a, b):

(x', y') = ([x - a] * scale + a, [y - b] * scale + b)

Fetch the original pixel data using pixelArray[y * width + x] as before, and set the destination pixel similarly with the new coordinates.

EDIT: you may also want to look at bilinear interpolation, because the current raw method may give jagged edges in the final image if used directly.