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In article <slr### [at] linux parkerr fwi com>,
ron### [at] povray org wrote:
> >> -1 0 0
> >> 0 1 0 * .5 + .5
> >> 0 0 0
> >
> >The numbers in the matrix above are correct. I'm not sure about the
> >multiplier and offset modifiers. For me, a vaue of one for the
> >multiplier works, and the offset value should be set to one-half of
> >the maximum possible value. I just tested these, and they work.
>
> A multiplier of 1 can cause clipping at the ends of the range. The
> two worst-case values of the matrix are -1 (when the upper-left pixel
> is white and the center is black) and 1 (vice-versa.) To get this range
> into the 0..1 range requires multiplying by .5 and adding .5, as I did.
This sounds like it would best be done as a simple macro using
blur_matrix(which should probably be renamed to "convolution_matrix",
since it can do more than blurring and it seems to be the common name).
> A better way to increase contrast would be to apply the
> filter as I've specified it, then apply an S-curve-shaped correction
> to stretch the midrange.
I have been thinking about this...is there a "standard" curve used for
this, or should I just come up with something?
--
Christopher James Huff - Personal e-mail: chr### [at] yahoo com
TAG(Technical Assistance Group) e-mail: chr### [at] tag povray org
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/
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