Saturday, June 14, 2008

2D Plot

When I am tired of sitting in front of the computer, I have two options. If I go to the countryside, I see litter along the roads, and that's not an inspiring sight. If I go to the harbor, it's more romantic, thanks to the water that covers and hides what's below. I know that there can be plenty of litter under there, but it's invisible and I enjoy the scenery. In NMR spectroscopy, 1D plots are the countryside, where you are forced to see the noise, 2D plots are the seaside. When I was a beginner, I was tempted to dry the sea to observe the hidden treasures. I found none. There's only litter at the bottom. Now the level of my spectroscopic sea is sensibly higher, but I am still the master of the tide and keep playing with it.
The computer programs are obsessed with the idea of expressing the intensity of the signals through color. I have already discussed this point in the past. There are two kinds of plots to consider. One is the bitmap or fast plot (like a photo), the other is the contour plot (like an ink drawing). In the first case you can have an (almost) continuous gradation of hues. I only use the bitmap for processing and I don't care too much about the colors. All I ask is that positive and negative peaks are well differentiated.
The contour plot, though slower and less informative, is more synthetic and, therefore, readable. I can both raise the tide from below and truncate the mountains from the top, remaining with only the shape of the islands. Most of the times, I keep 9 positive levels and 3 negative levels, in geometric progression (factor = 1.4).
I try to be as consistent as possible, while the programs encourage customization and babelization. You may find it funny to print a plot in 24 colors, I find it unreadable.
With 4 colors you can show everything:
1 dark color for positive islands;
1 dark color for negative islands;
1 light color for positive cliffs;
1 light color for negative cliffs.
Two colors (after raising the tide and burying the cliffs) are even better.
While, in 1D, it's difficult to realize that points have a finite size, it's natural in 2D to realize that a point is actually a small tile. Graphic cards are also optimized to reproduce bitmaps. Bottom line: drawing a 2D spectrum is less problematic.


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