You can just put each value in multiple times (for example, to make it 2x bigger, put each value in 4 times - 2x in the horizontal and 2x in the vertical). Or you could try to get a smoother zoom by using interpolation of values. This website provides some little bit of details on image interpolation and should provide at least enough information for further research.

well...if instead of outputting each point once, you output it twice, the picture should be twice as big. However, since pictures are two dimensional objects, you need to stretch it in both directions. the simplest way is to repeat the data you have. so this:

The problem is that if you do this too many times, your image becomes VERY blocky - like when you zoom in on a picture on a computer. You may be able to interpolate the data points. I.e. if your original data is 0, 100,0, you may be able to calculate data points 'between' the original one, giving you something like 0,50,100,50,0 - which would give a smoother picture.

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors