Hi Dion,
there is quite a lot of tools available to visualize gridded data. I am
frequently using gnuplot. Gnuplot understands x,y,z (with z
corresponding to illuminance E_h in your case). Just make sure that you
add an empty line before starting the next row of values. So something like
x1 y1 E
x2 y1 E
…
x512 y1 E
x1 y2 E
…
That allows you to use splot (surface plot, e.g.
http://lowrank.net/gnuplot/plotpm3d2-e.html). You can then apply
falsecolor scales, add contour lines, and introduce interpolation in
case you want a “smooth” appearance. In fact I usually prefer a larger
grid visualized by squares. You may also consider a logscale to account
for the rather steep gradient - or, not as nice but more comprehensive,
combine two linear plots with different ranges.
When I generate plots for reports or publications, I am relying on the
pgfplots package in Latex these days, which offers everything (and a bit
more) that gnuplot does. But that makes sense only if you aim at
embedding the results in a document.
There are many other tools around, and there is a lot of open source
software for scientific data visualization. Gnuplot has the advantage
that (although it appears cryptic in the beginning) you can achieve a
lot with few lines, and that you can reuse these with other datasets.
Cheers, Lars.