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tweaks of snohalo1 comments

This commit is contained in:
Nicolas Robidoux 2010-01-27 13:32:15 +00:00
parent 992386d55d
commit 8d17720212
1 changed files with 21 additions and 15 deletions
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36
libvips/resample/snohalo1.cpp
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@ -2,10 +2,9 @@
*
* Snohalo = "Smooth Nohalo" = Nohalo with custom antialiasing blur.
*
* Tweaks by N. Robidoux and J. Cupitt 01/04-29/05/09
*
* Major changes by N. Robidoux based on additional code by
* N. Robidoux, Adam Turcotte and Eric Daoust 26/01/10
* When blur = 0. (minimum value), Snohalo level 1.5 gives the same
* results as Nohalo level 2. At the maximum reasonable blur value
* (1.), very strong antialiasing takes place.
*/
/*
@ -36,12 +35,13 @@
*/
/*
* 2009-2010 (c) Nicolas Robidoux
* 2009-2010 (c) Nicolas Robidoux, Adam Turcotte, John Cupitt, Eric
* Daoust.
*
* N. Robidoux thanks Minglun Gong, Ralf Meyer, Geert Jordaens and
* Øyvind Kolås for useful comments and code.
*
* N. Robidoux's research on Nohalo funded in part by an NSERC
* N. Robidoux's early research on Nohalo funded in part by an NSERC
* (National Science and Engineering Research Council of Canada)
* Discovery Grant.
*
@ -109,7 +109,7 @@ typedef struct _VipsInterpolateSnohalo1Class {
* areas, since a, which is a pixel difference, will often be 0, in
* which case both forward branches are likely:
*
* ( (a_times_b)>=0.f ? 1.f : 0.f ) * ( (a_times_a)<=(a_times_b) ? (a) : (b) )
* ( (a_times_b)>=0 ? 1 : 0 ) * ( (a_times_a)<=(a_times_b) ? (a) : (b) )
*
* For uncompressed natural images in high bit depth (images for which
* the slopes a and b are unlikely to be equal to zero or be equal to
@ -119,15 +119,21 @@ typedef struct _VipsInterpolateSnohalo1Class {
*
* instead. With this second version, the forward branch of the second
* conditional move is taken when |b|>|a| and when a*b<0. However, the
* "else" branch is taken when a=0 (or when a=b), which is why the
* above version is not recommended for images with regions with
* constant pixel values (or regions with pixel values which vary
* bilinearly, as may be the case with cheap demosaicing).
* "else" branch is taken when a=0 (or when a=b), which is why this
* second version is not recommended for images with large regions
* with constant pixel values (or even, actually, regions with nearby
* pixel values which vary bilinearly, which may arise from dirt-cheap
* demosaicing or computer graphics operations).
*
* NOTE: Both of the above are better than FAST_MINMOD (found in
* templates.h), but MINMOD uses different parameters and consequently
* is not a direct substitute. The other methods should be modified so
* they use the above new version.
* Both of the above use a multiplication instead of a nested
* "if-then-else" because gcc does not always rewrite the latter using
* conditional moves.
*
* Implementation note: Both of the above are better than FAST_MINMOD
* (currently found in templates.h and used by all the other Nohalo
* methods). Unfortunately, MINMOD uses different parameters and
* consequently is not a direct substitute. The other Nohalo methods
* should be modified so they use the above new minmod implementation.
*/
#define MINMOD(a,b,a_times_a,a_times_b) \
( (a_times_b)>=0. ? 1. : 0. ) * ( (a_times_b)<(a_times_a) ? (b) : (a) )