2d grid interpolation

Question

I have a task of interpolating a 2d array of NxM to AxB, where A > N and B > M. The point of it is building a simple color coded image of an array (heat map).

Do I understand correctly that, for example, an array of 3x3 (all known values)

A B C
D E F
G H I

Should be interpolated in, say, 6x6 in this manner

A x B x x C
x x x x x x
D x E x x F
x x x x x x
x x x x x x
G x H x x I

where x marks unknown yet interpolated value, right?

Can this be done in two nested for loops? I found bilinear interpolation formula, but having some trouble with adapting it to (i, j) of resulted array loop. Any advices? Thanks in advance.

"Should be interpolated in, say, 6x6 in this manner..." That's a judgment call. As I'm sure you've discovered there are many resampling methods - en.wikipedia.org/wiki/Resampling_%28bitmap%29 - and the one you choose depends on a lot of factors. — Jordan Running
Even considering my heat map task? Result I need is similar to this upload.wikimedia.org/wikipedia/commons/c/c6/Bilininterp.png — spacevillain

Stefan Monov Stefan Monov · Accepted Answer · 2011-10-17T08:09:27

You could use a library like .NET, Qt or SDL to do it, it's a common application task.

If you want to implement it yourself, read about Bilinear filtering rather than bilinear interpolation. "Interpolation" generally means you interpolate just between two values - once you have an image, it's called filtering.

Consider nicer looking filters such as bicubic, too.

2d grid interpolation

1 Answers