There is basically 2 concepts here
- Horizontally means in my opinion that it works on rows, not on columns
- Linearly means that given two points that you actually know, all points in between are interpolated by having a value between value of pointA and value of pointB, and then the whole distance is basically 100%. If the new pixel is at distance 30% it will probably get the value that is there. Its basically what linear interpolation is ...
