On Sat, 15 Sep 2001, Sidik Isani wrote:
> Keith Packard wrote:
> |
> |
> |Around 10 o'clock on Sep 15, Sidik Isani wrote:
> |
> |> Unfortunately, there is. We look at astronomy CCD images, and
> |> the visualization tools like to manipulate a colormap to give a
> |> quick contrast adjustment.
> |
> |If you have source, you could consider fixing these to use DirectColor
> |instead; that would permit adjusting the luminence curves on the fly.
> |But, I suspect you also like to switch colors around, which this would not
> |do.
>
> It may be enough. Usually we look at our images with simple
> grey scales, and just need a way to exaggerate contrast to bring
> out features. I'd like to learn more about DirectColor. How much
> control does it give over luminence curves? Which XFree86 drivers
> support it (at depths > 8bpp)?
Most drivers support this for depths > 8bpp. NVIDIA and Matrox
at least, probably alot of others. TrueColor is essentially three
palette lookups with the indicies for the 3 channels (Red, Green and
Blue) being extracted from the pixel according to the RGB masks.
The difference between TrueColor and DirectColor is that you can
change the lookup tables with DirectColor. Still, there is only
one hardware palette so you get flashing when changing focus between
TrueColor and a DirectColor window. If you just want to change
the contrast a little this is not so annoying. Switching colors
around or heavy thresholding, while possible with DirectColor,
will suffer the same flashing consequences as private PseudoColor maps.
>
> |I assume these tools are creating their own colormaps; if this is the
> |case, you might consider using StaticColor for the default visual, this
> |would avoid flashing among the other windows while still permitting the
> |display to run at 8 bits.
>
> Thanks. I'll give that a try too.
But of course, the StaticColor palette is a simple color cube
and might not give you the range of colors you need. Certainly not
a good number of greys. And in the overlay mode only PseudoColor and
GrayScale visuals are offered, not StaticColor. That is because the
transparency key steals a color and only in the read/write maps can
the key be preallocated.
Mark.
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