On Tue, 02 May 2000 20:48:21 -0500, Chris Huff wrote:
>Stuff I don't know how to implement, and don't think I can figure out, 
>but which I think is useful, information on these would be welcome:
>    emboss

This is a matrix function, as long as you do it along one of the eight
multiples of 45 degrees.  For the usual "light in the upper left corner"
effect, I believe the operation is
  
 -1 0 0
  0 1 0   * .5 + .5
  0 0 0 

That is, if the pixel up and to the left is darker than the current 
pixel, the result is brighter than .5, and if it's lighter the result
is less than .5.  

>    dither/halftone

Floyd/Steinberg is fairly easy to implement, if I remember correctly.

>    sharpen_edges, and other "sharpen" filters. Blurring is pretty easy 
>to figure out, but doing the opposite has me lost.

The basic "sharpen" filter is also a matrix convolution, but what it
is escapes me for the moment.

>Stuff I don't even know the use for, let alone how to implement. Could 
>anyone tell me what these are for?
>posterize

This essentially quantizes the colors and makes a banding effect.  If I
remember correctly, it requires two passes: one to accumulate the colors
used in the image, and one to do the actual posterization.  In between,
you need to do some kind of color reduction step.

>laplace

I believe this is an edge-detection algorithm.  It might even be a 
matrix convolution.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
These are my opinions.  I do NOT speak for the POV-Team.

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