In article <slr### [at] linuxparkerrfwicom>, 
ron### [at] povrayorg 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] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

Post a reply to this message