From: Danny Shevitz <shevitz@la...> - 2005-08-02 21:33:46
>You are right. The problem is that a lookup table is quantized, and the
>thresholds/intensities are floats.
>In my particular case, what I'm looking at is an image representing
>arrival times. The problem is that
>the rounded down quantization gives me a peek into the future, which I
>don't want. The way I am suggesting
>with the ceiling suffers from exactly the same problem, as you mention. If
>you were looking at lower thresholds
>instead of upper thresholds then the ceiling would fail. That is why I was
>suggesting a switch for both behaviors.
>Since this is so obscure hardly anyone would use it or even need to know
>But... your last idea is superb. Why not a different way of doing it? How
>about instead of a lookup table, I just
>write a colormap that has three user defined functions. Then I could do
>the thresholding exactly. It seems like
>it would be pretty easy to do. I had originally thought colormaps were
>needed because graphics drivers had finite resolutions
>so you couldn't put up too many colors. So, if I were to create a
>"functionColormap" instead of a "linearSegmentedColormap"
>with millions of points in the image is there a danger I would run out of
>colors or is there some internal rounding or truncation
>to prevent this? If there is no problem, then a new colormap subclass is
>definately the way to go. I assume it would be slower, but
>I'm not sure it matters.
>>Isn't the essence of the problem the fact that the thresholds are
>>specified as floats and the lookup table is quantized by its nature? (And
>>that the current design allows for arbitrary N.) Whatever value you
>>specify for a threshold (unless it it 0 or 1) won't necessarily
>>correspond to a clean boundary between the quantized values (however you
>>choose to define the boundary: floor, midpoint, or ceiling). Isn't it
>>possible that your ceiling version has the same problem the other way
>>(some values that are actually less now show up above the threshold)?
>>I'm wondering if some other approach isn't needed. But before going into
>>more thought about that I'd like to clarify your usage.
Get latest updates about Open Source Projects, Conferences and News.